Radial Engineering | PreMax 500 Series | User manual | Radial Engineering PreMax 500 Series User manual

Radial Engineering PreMax 500 Series User manual
Modular Processing Supplement
V13.5 JULY/AUGUST 2014
26 Review: Radial Six Pack
& Powertube
28 Review: API Lunchbox 8C,
505-DI & 565
30 Review: Roll Music Valvop
30 Modular processing gear
39 Inside and behind the rack
Radial Six Pack
& Powertube
Radial has yet another rack and yet another module to add to its
portfolio of 500 series units. JON THRONTON
he Powertube is one of
a rapidly growing
number of 500 series
The range, comprising
repackaged versions of
existing Radial boxes
plus some brand new
additions now numbers
some 18 different modules
— no doubt due in part to
the introduction of its own 500
series chassis products under
the ‘Workhorse’ banner (And
there are six variations of the
racks. Ed). The most recent of
these — the Six Pack — was
used for the review, and that’s
important as it unlocks features
in the Powertube and other
Radial 500 series modules that
other chassis designs may not.
As its name suggests,
the Six Pack is a compact
chassis that houses up to six
compatible modules and in
broad terms these are any 500
series modules. An external
power supply connects via a
five-pin XLR connector, and
the supplied carry handle can
be attached to the top or the side of the chassis
depending on preference. Of particular note is the
capacity of the supply — 1600mA is available to
share between the six slots.
At one level it looks pretty straightforward, a
balanced input and output to each card are provided
on XLRs and ¼-inch TRS jacks wired in parallel
but Radial has added some interesting tweaks to
this standard theme. For ease of connection to, for
example, a DAW interface, eight inputs and outputs
are also provided on DSUB connectors. The first six of
these logically connect to the six slots, the remaining
two inputs from the DSUBs are available on the rear
panel on balanced jacks, and a pair of additional
front panel XLRs can be routed to the ‘spare’ DSUB
Each of the six slots also has a slide switch on the
rear panel allowing it to feed its output to the input
of the next slot along — useful for recording chains
made up of individual modules without a mess of
patch leads at the rear. But perhaps the biggest
change — and one that moves slightly away from the
original ‘standard’ — is the provision of an additional
rear panel connection for each module, dubbed
the OmniPort. A ¼-inch stereo jack, the Omniport
function is entirely down to the module manufacturer.
For example it could be used as an (unbalanced)
sidechain access point for a compressor, as an
external key-input for a gate, an insert point or an
additional input. While the majority of Radial’s own
modules obviously exploit this feature, they are also
encouraging other 500 series manufacturers to adopt
it by publishing the specs in an Open Source document
(Workhorse Open Source Document).
The Powertube module is a
tube-based Class A preamp. Front
panel controls are extremely
straightforward — a continuously
variable pot effectively trims the
input to the initial tube stage by
up to 60dB, while another pot sets
up to 60dB gain from the discrete,
Class A output stage. Output level
metering is via a 10-segment LED
ladder working across a range of
-20 to +6dBu. Given that the
aforementioned gain staging is
clearly an inducement to drive
the Powertube as hard as you
dare, it would have been useful
to have the upper range of this
extended somewhat. The display
is also configured so that only one
segment lights at a time, rather
than building up from the left hand
side. This works fine up close, but you do lose the
sense of ‘size’ of signal when squinting at a distance.
Below the gain pot are two pushbuttons to engage
filters in the signal path. The first is the ubiquitous
HPF (100Hz @ 6dB/octave), while the other, labelled
‘Air’, adds a gentle presence boost centred around
8kHz or so. Finally, a recessed pushbutton (you
resolution need a pen/matchstick/tweaker to operate it) engages
phantom power. While I can see the thinking behind
this in terms of reducing the chance of accidentally
applying phantom to an aged ribbon mic, after a
while it can get a little tiresome hunting around for a
suitable poking implement.
As well as the front panel controls, there are a
couple of slide switches on the rear of the PCB at the
back of the module. The first of these is a hard earth
lift on the inputs — only really useful for feeding line
level sources or dynamic mics at a push, as phantom
power is going to disappear if it’s engaged. The second
determines which of the two audio power rails will be
used to power the tube’s heater (+16 or -16V). This
enables this part of the total module current draw to
be balanced between the two rails — useful if your
chassis is populated with multiple Powertubes.
Internally, the Powertube uses a Jensen input
transformer that feeds a 12AX7 tube, followed by
a Class A discrete gain stage. If the Six Pack chassis
didn’t already provide enough input options, there’s
also a front panel XLR input on the module itself. The
OmniPort function in this case provides a DI input on
the rear — inserting a jack in here engages a relay
that disconnects the balanced input and presents the
DI input directly to the transformer.
Plugging in a C414 for reference, and with the
trim control set halfway, initial impressions are of a
robust sound that’s reasonably quiet and open. Noise
does increase as the trim control is turned up and the
tube stage driven harder, along with progressively
increasing amounts of harmonic distortion. Adjusting
the relative settings of trim and gain gives a very
broad palette of sonic permutations, ranging from
clean to slightly warm to positively grungy on
line level sources (which the Powertube deals
with quite happily). In practice, unless really
going for effect, I found that the best results on
most sources were found in the bottom half of the
trim control’s travel. Nevertheless, Radial also ships
an additional ToneBone distortion pedal tube with
the module for additional possibilities (the tube is
socketed on its own circuit board inside the module,
so swapping it out is pretty straightforward). The ‘Air’
presence boost is a useful feature, particularly when
exploring the cleaner end of the tonal range. It’s a
fairly subtle little boost, but actually more generally
useful as a result.
I was less enamoured with the DI input which
sounded a little too ‘soft’ for some applications — I
suspect as a result of the relatively low (150kOhm)
load impedance of the DI stage. While this gave a nice
smooth tone on DI bass, it lacks a little detail on other
sources, although dialling in a little extra tube drive in
conjunction with the Air setting helps here.
The Powertube is unashamedly old school in
approach, and coupled with the no-nonsense we’ve
come to associate with Radial Engineering, it’s safe to
say that it isn’t something you are going to turn to for
subtlety. But for a flexible, characterful and compact
preamp it will find a lot of friends. n
Wide sonic palette; robust sounding; flexible
gain staging for working with line and mic
sources; Air filter subtle and useful; flexible
routing and I-O options on Six Pack
DI input a little ‘soft’ sounding for some
applications; metering could have a wider
range; phantom power switch a bit fiddly.
Web: www.radialeng.com
July/August 2014
API Lunchbox 8C,
505-DI, 565
In a rare flurry of activity API has launched a new 500 series power
rack and a pair of new 500 Series modules. GEORGE SHILLING
f course, API invented the modern modular
500 series format many years ago, but in
recent times there has been an explosion
of third-party racks and modules to rival
the originals. These new additions perhaps represent
something of a response from the proud parents.
Lunchbox 8C — The 8C uses an apparently similar
sized case to the existing 6-slot Lunchbox design (the
500-6B) but adds a further two slots. Amazingly, the
price of the 8C is exactly the same as the still available
6-slot version but you will not be surprised to learn
that there have been some compromises to achieve
the price point. The PSU is now outboard and this has
freed up the space for the two extra slots. An inline
brick is unusually actually badged as API, which is
most helpful when rummaging around racks and
boxes of PSUs. It has an IEC inlet socket and supplies
power with a five-pin female XLR on a flying lead
to plumb into the back of the rack case. A casualty
of this change is the missing Power button — there
is none, front or rear, which might be a nuisance,
particularly if you want to install valvebased third party modules and don’t want
them permanently switched on. Apart
from the aforementioned power connector,
there are no XLR connectors on the
rear of this box; inputs and outputs are
now accessed solely with a pair of DB25
connections. Clearly costs have been
saved here but you do get a set of toggles
to feed audio from each slot to the one
on its right, albeit less than conveniently
placed on the rear panel. The rack unit comes supplied
with a large handle bolted to the left side, and rubber
feet on the opposite end and the bottom allows for
either orientation. A rack ears kit is available, so
if you remove all those accoutrements and follow
the necessary instructions, you can slot this into
a 19-inch space, 3U high, although you might
want to consider the (albeit rather pricier) dedicated
19-inch 500VPR 10-slot model with integral PSU.
Bear in mind though, as you bolt this into your rack,
you’ll likely be saying farewell to those Link toggle
switches. There are modern rival units with more
whizz-bang features, but at UK£341 + VAT this is
keenly priced, reassuringly sturdy, and should ward
off some of the competition.
Good value — lower price per slot than rivals
from the inventor of the 500 series format.
Only DB25 connections; no power button.
505-DI — This module appears to
expand on the concept of the 205L
which is a 200 Series module, the
‘baby brother’ format to the 500
Series used in current large format API
consoles. No input signal is derived
from the 500 Series rack rear, you must
instead plumb something into the front
panel instrument jack labelled Hi-Z In,
the socket ingeniously illuminates from
within the hole by a blue LED. This is
a gimmick, but it does help you easily
identify the correct socket from the
excellent addition to the 205L: a Thru
jack socket, which simply parallels
the input. This feature is very useful in a recording
scenario, e.g. when tapping off a DI bass guitar
signal for recording but also routing it onwards to an
amplifier. On the host rack, this DI module outputs
line level signal, so you can feed this straight to the
recorder. A blue topped Gain knob at the top is scaled
0 to 10, but this is not a fader, i.e. turning it to zero
does not mute. It does provide oodles of boost though
(up to 55dB of gain) and there is an excellent clearly
labelled 10-segment LED meter (plus a Peak LED) to
keep tabs on the output level.
A white Tone knob is calibrated as Thin on the left,
Fat at the top, and Fatter at full-tilt. In actual fact, this is
a mud-removal shelving EQ circuit, with anything less
than Fatter reducing sub 150Hz signal by up to 12dB at
the Thin end. The Bright toggle switch boosts the highs
with a shelf from around 8kHz by about 7dB, adding
terrific life and sparkle to guitars. This is most welcome,
and like traditional API EQ doesn’t sound harsh or at all
spiky. An On button illuminates yellow when pressed;
this is a very handy way of quickly muting the output
before your talent plugs in or unplugs their end of the
jack cable. Further toggles provide a 20dB Pad that
apparently doesn’t affect the load — useful especially
for high output keyboard instruments — and a Load
selector to switch between 100kOhm and 400kOhm.
The latter setting is generally preferable; it’s subtler than
the Bright switch, but the former slightly darkened the
tone and reduced the level of my Telecaster.
The sound is solid, musical, and as reassuringly
smooth and stable as you come to expect from API.
The tonal variations available are useful, and it is
quick and easy to make decisions with just one Tone
knob and a couple of toggles to vary things. The
Bright circuit is smooth and brings an openness to
the tone. The Tone knob does a great job too, with a
beautifully linear gradation as you turn it to find the
sweet spot. Even when recording bass guitar, settings
lower than Fatter can usefully tame any low end
waffling. At £408 + VAT the 505-DI isn’t cheap, but
this is a tool of the highest quality.
Solid sounding DI preamp; line level output;
useful Thru jack; plenty of gain; flexible tone
No ground lift.
AWA R D S 2014
565 — This new module
comprises High Pass, Notch
and Low Pass Filters,
expanding on the 215 filter
module found in API’s large
desks. Unlike the 505-DI, the
565’s circuitry is completely
encased in thin steel. On the
front are four familiar looking
blue-topped API knobs. I love
API knobs; they look like
something from the TARDIS
and have huge protruding
pointers that you can steer the
knob round with. Unlike the
usual clicky switched settings
found on 550 EQ modules,
the 565’s are all continuous
sweeping pots with no
damping. The top one is the
Low Pass control, calibrated
from 500Hz to 20kHz. A tiny
toggle marked In enables the
filter, and there is a similar one to select between
-12dB per octave and -6dB per octave operation.
Some very gentle reduction of nasties is possible here,
or you can achieve more robust taming of unwanted
harshness. The next section is a variable Notch filter.
When the In toggle is enabled, the selected frequency
is notched out. At fully clockwise, the notch is pinsharp, as narrow as a needle (Q factor is quoted as
20) gradually widening towards a broader dip when
counter-clockwise. At the broadest setting, the Q
is 0.65, which cuts a huge 40-50dB swathe at the
selected frequency. The frequency is selected with a
knob calibrated from 20Hz to 200Hz, with a threeposition multiplier toggle for x1, x10 and x100,
thereby covering the entire audio spectrum while
allowing the user great precision. Sweeping with the
Notch near the narrow end creates a pseudo-phasing
effect, while turning the Notch further left allows great
wodges of the spectrum to be pulled out.
Finally there is a High Pass filter knob scaled from
20Hz to 600Hz, with an In toggle and a choice of
-12dB or -18dB per octave on another switch. This
works well for cutting out undesirable lows, and even
in its steepest mode manages to sound clean and
smooth. The filters don’t sound at all phasey (unless
you sweep a narrow Notch of course). Clearing
some low-end mud is always satisfying. Sometimes
counter-intuitively, clearing some ‘air’ with the Low
Pass is also surprisingly pleasant and doing this on
some instruments can help bind the mix. With the
High and Low filters almost meeting, you can get
some good telephoney sounding effects. All toggles
operate silently with no drama, and the knobs are
a pleasure to twiddle. This is a super-smooth and
wonderfully useful module with great sonic integrity,
and fabulous sounding filtering, all for £408 + VAT. n
Great sounding filters; powerful Notch
covering the entire audio spectrum.
Web: www.apiaudio.com
UK, Source: +44 208 962 5080
Roll Music Valvop
Simple and superbly characterful compression is what this unit is all about.
Recent module introductions.
Solid State Logic
The X-Rack Stereo EQ Module is a stereo version of
the XL 9000 K Channel Equaliser as used on Duality
and AWS consoles. It is a 4-band parametric EQ with
high- and low-bands switchable between shelving
or fixed Q bell curves and two mid-bands with
variable Q controls. The stereo version
introduces a ‘Selective Mode’ switch
that enables independent switching
of high and low bands and mid bands
between SSL’s E and G series console EQ
characteristics. Rear panel connections
are on balanced TRS jacks and Total
Recall status LEDs are included. The
X-Rack Stereo Dynamics Module
delivers the same sonic signature as the
channel strip processing of SSL’s large
format Duality console and the mono
X-Rack SuperAnalogue Dynamics Module in a stereo
configuration. The module is intended for stereo
tracking or stem mixing. The Compressor section
can switch between a gentle Soft Knee (Over Easy)
RMS compression to a more aggressive
Peak Sensing or Hard Knee mode, making for a wide
range of levelling control. The secondary circuit
can function as a Noise Gate or an Expander. The
feature set is complemented by an External Key
Input (mono), for triggering the unit
from an external sound source, and
the ability for multiple adjacent units
to be linked.
SSL also has 500-S format modules
of its E series Dynamics and EQ. The
611DYN reproduces the SL 4000 E
console channel strip with a compressor/limiter and
an expander/gate. An RMS convertor is used in the
sidechain while the gain element is a discrete design
identical to the Class-A VCA chip used in the original
unit. The compressor contains
additional switching options to defeat the
over-easy curve and to use a linear release
instead of the more usual logarithmic curve.
The 611EQ E series EQ Module has the two
different EQs found on editions of the console
produced between 1981 and 1989. The type
of EQ fitted in a console was distinguished by
the colours of the LF knob caps and became
known as Brown and Black. The module
allows users to switch between the two. It is 4-band with a bell
curve option on the HF and LF and parametric LMF and HMF
with Q. SSL’s Stereo Bus Compressor, the centre section from the
80s-vintage G series console, is also available in 500-Series format
as the G COMP module featuring six ratio settings and five release
settings plus an Auto Release function.
Sonic Farm
Silkworm is a solid state microphone and
instrument preamp. It uses a discrete servocontrolled gain stage and a transformer on input
and output. The output can be switched to a
solid state balanced line driver, bypassing the
transformer, for a more open sound. A 3-position
‘vibe’ switch enhances the tonal palette and helps
tailor the sound to suit an application.
oll Music Systems in Minneapolis originated
as a recording studio in 1998 but founder
Justin Ulysses Morse turned to gear design
and manufacture, with products available
since 2003. Best known are the RMS-216 Folcrom
passive summing mixer, and
the RMS-755 Super Stereo
V6.5) looked at previously.
A few years back they
turned to the 500 Series
format with the RMS-5A7
Tubule microphone preamp.
Similarly styled, using the
same amplifier circuit, and
officially called the RMS-MC5,
the Valvop (UK£700 + VAT)
is an optical valve compressor.
Built like the proverbial brick
outhouse, with ten screws and
four Allen bolts holding the
case together (Doesn’t sound
much like an outhouse to me.
Ed), it boasts a super-thick
stainless steel front panel, big
metal knobs, and old skool
latching ‘winkie’ pushbuttons.
This thing manages to look
big and proper, unlike most
fiddly 500 Series modules,
and feels incredibly well
screwed together. Internally,
a perpendicular circuit board
‘ledge’ is bolted onto the
main board for the mounting
socket for a JJ brand ECC832
valve, keeping it upright
when the module is conventionally orientated in,
say, a Lunchbox. I tested the Valvop in an API 8C
and a Radial Six-Pack Workhorse, and amazingly
the module’s circuitry manages to convert the input
power to the necessary high voltage (220V) to
properly drive the valve while staying well within
500 Series spec. Discrete components are mounted
on the main board, including some sizeable custom
transformers, and there are a further couple of small
‘ledges’, at least one of which includes surface
mounted chips.
The big black knurled Threshold knob is calibrated
with 11 dots; turning anticlockwise lowers the
threshold and increases compression. The similar
style knob at the bottom is switched Gain make-up
and this clicks between 12 positions (corresponding
dots on the panel) in 2dB steps from -2dB to +20dB.
The clicks are quite chunky and there is no danger of
accidental movement here.
Between the knobs are two buttons and a light.
PDR is Programme Dependent Release and switches
the compressor to a dual release mode where
compression of short transients recovers quickly while
long passages of loud material are given a slower
compressor release. The large amber light is actually
a big LED that glows to indicate gain reduction and
that’s all you get for metering. However, the light’s
intensity varies rapidly with the signal, and gives a
good indication of how the compressor will behave
resolution — this is an optical compressor after all. Below this is
a second pushbutton which bypasses the compressor
(but seems to add about 2dB of gain).
Roll Music suggests vocals and electric bass as
suitable applications. On a smooth alto female vocal,
which had been recorded with a touch of 1176,
the transformer-coupled Valvop immediately lent
a gorgeous warmth to the sound. Smooth and
rich compression is achieved but the sound
remains coherent wherever the
Threshold knob is, thanks
to a fairly fast attack.
Level reduction is easily
compensated for using
the Gain knob. The vocal
sat beautifully in the track
with moderately high
compression and little or
no level riding required.
similarities here to LA-2A
type units, especially in
PDR mode. This makes
the compression a little
less audible and pumping,
and the sound perhaps
even more smooth and
delicious. A punky, shouty
and slightly thin-sounding
high male vocal with
huge dynamic range was
satisfyingly thickened with
a hefty dose of PDR. Bass
guitar is indeed a great candidate
for some Valvop, sounding big, warm and
juicy but perhaps my favourite use was for acoustic
guitar. When compressing heavily, PDR mode reduces
some of the percussion of strummed chords for a
really smooth texture. If you want a bit more punch
from the guitar, then unlatching the PDR button
is the way to go. But either mode is gorgeous,
however hard you drive the compression — this unit
seems to invite you to go further and further, and
sometimes the maximum setting still isn’t too much.
A conventional meter would probably be worrisome
here, so it’s probably best that there isn’t one! The
amount of make-up gain to roughly match levels
was often at +12 or 14dB. The release is rather slow
for crazy drum ambience, but it successfully warmed
up a room mic, bringing a lovely low-mid glue to the
kick and snare.
Always a fan of rock music, I’m now also a fan of
Roll Music, and especially the Valvop, which is the
best and biggest-sounding 500 Series compressor
I’ve heard. n
Luscious valve optical compression;
PDR setting provides superb alternative
character; robust build; no fiddly toggle
switches; huge sound from a little module.
One of these might not be enough.
UK: KMR Audio: +44 208 445 2446
July/August 2014
Spotlight: Elysia
The most recent addition to Elysia’s line of 500-Series
modules are the xfilter 500 and nvelope 500. Elysia’s
xfilter 500 is a true stereo EQ with an all Class-A audio
path. It offers high- and low-shelf bands, both of which
can be switched into high- and low-cut filters with
resonance — a feature from the flagship museq EQ.
The xfilter 500 also provides two mid-peak filters with
wide or narrow Q. It has a switchable fixed LC filter
for the high frequency and this passive filter consists
of a capacitor and a coil per channel that produce a
slight resonance peak around 12kHz. By linking its
two channels, the xfilter 500 eliminates the task of
matching settings. The potentiometers are stepped.
The nvelope 500 is a two-slot-space stereo
dynamics processor capable of making subtle or
drastic changes to a sound by altering its impulse
structure, providing direct control over the envelope
of a signal by shaping the intensity of its attack and
sustain. It is primarily intended to shape individual signals, but it can be used in mixing as well. Another powerful feature is the
enhanced tweakability offered in Dual Band mode. Individual frequency controls for attack and sustain yield precise results
while avoiding unwanted artefacts — even when used on complex material like a summing bus. The nvelope 500 offers dual
mono or linked stereo operation in Full Range, Dual Band, or EQ modes.
Kush Audio
The DS101 500-Series noise gate features the
frequency conscious gating functionality of
Drawmer’s DS201. The DS101 is based on a single
channel of the DS201 and incorporates fully
variable high- and low-pass filters and key listen
monitoring. The DS101, which can be used for
gating and ducking, has controls for threshold,
attack, hold, decay, and range, as well as Drawmer’s
traffic light metering. When installed next to each
other in a 500-Series rack, two or more DS101
gates may be linked using Drawmer’s new infrared
triggering mechanism. Linked in this fashion, the
envelope shaping capabilities of many DS101 gates may be
adjusted independently while the trigger pulse passes through
Kush Audio’s Electra is a 4-band, ‘multitopology’
EQ that has two sweepable, overlapping
Proportional-Q bands whose bandwidth and
gain have been tailored to allow for extreme
pushes. Rounding out the bottom is a fixed
low shelf that interacts with the continuously
variable (25-400Hz) 12dB/octave HPF. Topping
it off is a sweepable (3.4-20kHz) high shelf
reminiscent of vintage mastering equalisers. A
switchable Fader Mode converts the low shelf
knob into a fader so multiple Electras can be
used to create lunchbox-based mixers with
fader and EQ. The popular Clariphonic Parallel
Equalizer has also received the 500-Series
‘shrinkage’ treatment to re-emerge as the
Clariphonic 500 with two high-shelves blended in parallel on
each channel; six corner frequencies; powerful control over the
midrange, presence, and air bands; and ability to solo the parallel
filters for external sweetening and processing.
The PWM -501 is an ultra -fast
compressor. With its Feed-Forward
and Fe e d - Back control, user s
effectively have access to two totally
different sounding compressors.
When engaged, a second order (12dB/
octave) variable HPF is inserted in the
sidechain immediately after the FeedForward and Feed-Back blend circuit
to filter out bass signals that might
otherwise influence the action of
the PWM-501. The Threshold control
determines the portion of the signal
that the rest of the sidechain will use
to control the operation of the PWM501. At low levels the unit looks at all
or most of the signal and acts as a
compressor; at higher levels it looks at peak and functions more as
a limiter. Alongside Ratio, Attack time, and Release time controls, a
Link switch links the control voltage between multiple PWM-501
units installed in a rack with the correct interconnections on the
backplane bus. One unit can be used to control all others, or each
can contribute. This control voltage is unique to the PWM-501
and is not compatible with systems from other manufacturers.
Display LEDs operate according to whatever meter mode is used.
July/August 2014
DAV Electronics
Inspired by the DAV Electronics BG 3 (Broadhurst
Gardens No. 3) mastering EQ, the BG 503 EQ is
a 500-Series module. Low and high frequency
bands use a shelf curve with +/-8dB of gain and
stepped frequencies ranging
from 12.5-400Hz for the LF
band and from 2-32kHz for
the HF band. The mid band
uses a resonant design with
its bandwidth narrowing
when reaching the extremes
of its +/-12dB of gain. Stepped
frequencies are also used
and range from 240Hz-5kHz
offering useful overlapping
of frequencies between bands. The BG 504
(Broadhurst Gardens No. 504) is an optical
limiter/compressor, featuring electronically
balanced inputs and outputs, low noise/
distortion, LED GR meter, stereo link, and a
total bypass.
Great River Electronics
N. London 020 8445 2446
Richmond 020 8492 9790
+49 30 2935 2426
1407 500 Series 68x260 Resolution FLAT.indd 1
30/06/2014 21:27
The RPQ500 is based on the full-rack RPQ
preamplifier and provides the same ultra-clean,
high-gain signal path, but with enhanced
and additional features for compatibility with
a 500-Series rack. With 80dB of JFET gain and
NoLoad input impedance, the CurveShaper
offers a natural option for sculpting sound at the
start of the signal path. Switchable and tuneable
LF and HF contour controls allow engineers
to tame proximity problems and provide HF
extension and slope control. The high-frequency
CurveShaper excels in adding a touch of air or
presence, and the low-frequency control can
remove boxiness. The Line/Mic switch bypasses
the microphone gain stage and allows the EQ to be used for
tracking with other preamps or during mixdown.
AnaMod’s XF Tube processor is a model-based
analogue processor that emulates a two-stage
tube and transformer amplifier. The XF Tube was
created using the AnaMod Process, which uses
mathematical models to synthesise analogue
hardware — in this case, a tube amplifier. Unlike
digital plug-ins or processor-based outboard gear,
there is no latency and no A-D or D-A
conversions. AnaMod also has the
Realios line of microphone preamps.
The A9031 and A9033 represent
very different types of microphone preamps. The
A9031 is a copy of the vintage Dick Swettenham
Helios design, as modified and used by Lenny
Kravitz and his engineer Henry Hirsch. The A9033
is a new concept for a microphone preamp and
gain is obtained entirely from step-up transformers
and uses no negative feedback. Both preamplifiers
are Class-A and discrete transistor. The AnaMod
Process was also put to use on
AnaMod’s A9052 equaliser, a companion 500 Series
module to the A9031 Olympic-style microphone
preamp, said to be a faithful recreation of the
Olympic recording desk equalisers with the
addition of wider dynamic range and output
drive capability. The equaliser can
handle signals roughly 6dB greater
than would normally be allowed in
the 500-Series due to a step-down
input transformer and step-up
output transformer, and features the
original Olympic 3 transistor gain
make up circuit as well as a new Class A output
drive circuit. AnaMod’s TLCompressor (Tungsten
Lamp Compressor) is also part of its Realios line
and uses a Tungsten lamp for levelling the gain
of an audio signal. This represents a method of
audio compression unlike any other and provides
distortionless, artefact-free operation for female vocals, bass,
and mixes.
Pendulum Audio
Pendulum Audio’s DS-500 Opto De-Esser is a
single-channel, non-tube version of the de-esser
in the Pendulum Tube Recording Channel. It uses
the same inductive detector and opto-inductive
notch filter so it has the same characteristics and a
very fast response. By pairing it up with a unity gain
Class-A solid-state line stage, the DS-500 retains the
transparent character of the de-esser action, while
keeping the signal path clean and uncoloured.
Spotlight: Phoenix Audio
Phoenix Audio’s N90-DRC/500 is a 500-Series format compressor and gate designed around
a VCA with Class-A discrete input and Class-A transformer-balanced output. The progressive
curves are achieved using linear detection combined with logarithmic attenuation inside
a closed control loop with limiter sound provided by the higher ratios and there is a choice
of attack times. The gate is more conventional, but its release time is composite with a hold
time followed by a fade time. The DRS-1R/500 mono preamp and DI shares the same feature
set and sonic characteristics as its popular ‘big brother’, the DSR-1, yet runs at 24V, thanks
to a special inbuilt power supply.
The DRS-EQ/500 is a mono 4-band EQ. It is designed to be identical to the other Phoenix
products in terms of features and sonic characteristics, and includes the same EQ circuit
found in the larger DRS-Q4 mk2 Class A Discrete Mic-Pre/DI/EQ. The Gyrator EQ circuit was
originally designed around 40 years ago to emulate the characteristics of a coil or inductor
EQ circuit without their inherent issues.
Aphex’s USB 500 Rack bridges the gap between the analogue
500-Series and modern DAW workflows by providing a solution to
use 500-Series modules directly with a DAW via USB. Mic preamps
can be used as direct DAW inputs or analogue compressors and
EQs can be used as hardware inserts while monitoring through
the monitor section of the USB 500 Rack that includes Mono
and Dim functions along with two independent headphone
amplifiers. Modules can be chained in the analogue domain for
channel strip operation or linked for stereo compression. The
USB 500 Rack also provides balanced XLR connections for use
as a standard analogue 500-Series rack. Additionally, Aphex bills
its D 500 DUO two-slot receiving frame as being like no other,
providing balanced analogue insert jacks to connect processors
like equalisers and compressors when two preamp modules are
loaded into the rack. If no processors are inserted, the insert send
can be used as a secondary output for the module. An SPDIF
output derives its signal post-insert to allow for a processed mic
pre signal to be converted to digital and sent to a DAW or digital
recorder. Analogue and digital outputs are always active.
Aphex now has
eight 500-Series
modules: JPre
500 Mic Pre; EQF
500 Parametric
Equaliser; Dual
RPA 500 Mic Pre;
A PRE 500 Mic
Pre; COMP 500 Optical Compressor; EX BB 500 Aural Exciter/Big
Bottom; CX 500; and Project 500. The JPre 500 Mic Pre is inspired
by the Aphex 1788A remote controlled preamp while the EQF 500
reissue is a modern take on the Aphex EQF-2 500-Series 3-band
equaliser originally introduced in the 80s. Most recently released,
the 500 is based on the CX-1 compressor/gate unit — one of the
first 500-Series modules, and features the company’s patented
EasyRider compressor and logic-assisted gate, a Jensen output
transformer, and multifunction meter for gain reduction, gating,
and output level. The Project 500 is a 500-Series module-sized
version of Aphex’s Project Channel rack unit. A full channel strip,
it includes a Class-A mic preamp, optical compressor, and dualband semi-parametric EQ.
resolution AwTac’s Channel Compressor is a FET compressor.
Transformer-balanced inputs and outputs deliver a
big iron sound while discrete transistor amplifiers
are used in the audio and sidechain circuit. The FET
sidechain affects the gain of the input amp and
offers smooth sounding compression akin to that
from optical compressors. It uses an adaptive ratio
of around 10:1, but starting at 1:1, transitioning to
1.5:1 at the bottom of the soft knee slope, it then
increases to 2:1, 3:1, 4:1, 6:1, and finally 10:1. The Gain
Reduction meter, in addition to showing how gain
reduction is happening, also indicates the ratio being used. The
first -0.5 LED indicates a ratio of 1.5:1, the -1dB indicates 2:1 — all
the way to -15dB, where the compression will behave as a limiter
with a 16:1 ratio. A Blend control enables users to use parallel
compression. Unlike traditional mix/dry knobs or crossfaders,
the Blend control adds the dry signal back into the compressor
while the Output pot controls the amount of compressed signal
being let through. Both signals are then sent to an internal
summing amp.
The AwTac Channel Amplifier is a double-width 500-Series
module with an LCR (left- centre- right-selectable) passive mix
bus — just like most mixing consoles up to the late 60s. Its extra
width enabled its creator to include an extra set of I-O jacks for a
mix bus — connect one Channel Amplifier to another to create a
mixer. Other notable features include a line level amplifier, 3-band
EQ (with three-frequency Baxandall high and low shelf and an
inductor-based 10-band midrange), as well as a DI box.
Buzz Audio
Buzz Audio’s proprietary A-Rack 8+1 can house up to nine
of its MA-1.5 mic preamp modules. These modules feature
almost identical circuitry to the company’s True Class-A NA-2.2
microphone preamplifier, except that the output is electronically
balanced. The A-Rack is designed for multichannel recording
setups and the MA-1.5 preamp module delivers a punchy and
detailed sound. Controls include Gain (+22dB to +70dB minimum
in balanced mode, +16dB to +64dB minimum in unbalanced
mode), Mute, Phase, Pad, In Z (input impedance), and 48V on/off.
As well as the solo monitoring function, each module has a peak
indicator that lights up when the output level reaches +18dBu.
Quoted frequency response is 2Hz to 250kHz @ 20dB gain (-3dB)
and 20Hz to 250kHz @ 65dB gain (-3dB) with harmonic distortion
of less than 0.008% (100Hz to 10kHz).
July/August 2014
Cartec Audio
Chandler Limited
Empirical Labs
Cartec Audio’s Compere 500-Series enclosure has 8 slots with an
internal power supply providing 3A per rail. It has an assignable
front panel input XLR in addition to the 8 input and output XLRs.
Users can introduce the front panel input signal to any one of the 8
modules via the front panel Aux to the input module rotary switch
and associated 48V phantom power switch. This is intended
to provide uninterrupted phantom power when switching to
different preamp modules. The Aux to output module rotary
switch selects which module carries the output and the audio
appears on the dedicated rear mounted routing section output
XLR. The regular module’s XLR I-O audio path is defeated while
the Aux Compere function is activated for that module. At the
rear of the rack each module slot has a link switch that routes
the output of a module into the input of the next module slot
on the right. Cartec manufacturers two 500-Series module. The
PRE-Q5 is a transformer-based preamp
that incorporates a passive inductor
equaliser and a balanced output
attenuator. The circuit is identical to
the larger PRE-Q1A two-channel highquality transformer-based microphone
preamplifier, but without the High/Low
boost front panel controls. The FE-Q5
is an inductor-based equaliser that
incorporates a discrete amplifier stage,
a 12dB/octave HP filter (independent
of equaliser with its own discrete
Op-Amp), and custom-wound input and output transformers,
plus two multitap inductors and two Op-Amps.
Chandler’s TG2-500 preamp builds upon the
TG2 preamp/DI, which delivers the sound of
the EMI TG12428 preamp used in EMI/Abbey
Road recording and mastering consoles in
the late 60s and early 70s. Using the identical
TG2 circuit, transistors, and transformers, the
TG2-500 delivers 10-60dB of gain and uses a
coarse gain control and a fine gain control as
found on EMI consoles. The unit provides 300
and 1200Ohm input impedance as on the TG2.
As such, the TG2-500 delivers
frequency response identical
to the TG2 and has the same
high frequency bump and mid
forward tone that users enjoy with the TG2.
The Germ 500 MKII is Chandler’s well-known
Class-A, discrete, transistor Germanium Preamp
adapted for 500-Series racks. It uses the same
transformers and amp blocks to
ensure that it sounds consistent
with the ‘full-size’ rack version
and offers -5dB to +65dB gain
and a transformer-balanced mic
input with 300Ohm impedance.
The 500-Series format Little
Devil Pre Amp’s Class-A gain stage sounds big,
open, and full of life. Just about any parameter
of the sound is changeable, including the
ability to change both the Feedback and Bias
of the amplifier. The Feedback control increases
harmonics over the range of the control. Other
features include High and Low input impedance,
transformer-balanced line in for using the unit as a colour box on
mixes or tracks, low cut, and a bright switch.
DocDerr is a 500-Series channel strip with six different sections
of digitally controlled analogue processing. A low-noise preamp
capable of line or 16dB of instrument gain is followed by four
sections of EQ offering one selectable high pass and three
parametric bands. The dynamics section provides Empirical
Labs compression and a tape emulation circuit to soften high
frequencies and clips. A Mix knob allows the user to blend the
uncompressed EQ signal with the compressed and saturated
signal. Inputs and outputs are DC coupled, and the output can be
switched between single ended or differential, yielding +/-6dB
of gain.
At the heart of Empirical Labs’ 1U EL500 rack is a super quiet
power supply to ensure optimal performance from any 500-Series
compatible device. Two can be accommodated side by side and
will flush mount. Additionally, a 1/4-inch instrument preamplifier/
DI box is integrated into the front panel. To ensure the best
possible enclosure/power supply combo for its own 500-Series
modules, Empirical Labs can preload and bundle its DerrEsser
and DocDerr modules in any mono or stereo combination along
with its EL500 rack.
Empirical Labs
also caters to the
5 0 0 -S e r i e s D I Y
community with
it s Proto50 0, a
prototyping system
for the API 500-Series powered rack system. It includes a PCB card,
a metal front panel with mounting positions, and five switches,
as well as a user manual. With more than 2700 pads and pre-laid
out power supply traces, users can prototype relatively complex
circuits for the 500-Series with relative ease. Front panel graphics
can be pressed or silkscreened on for a professional look to match.
00 - ste
reo imp
ulse sh
r 500 -
or xflt
er 500
Big in sound and features.
Compact in size and price.
Experience superior class-A
dynamics and equalization:
July/August 2014
SM Pro
The MBC502 is an optical multiband
compressor. The LF and HF channels
each of fer controls over level,
compression and attack and release
times. Switches allow you to mute one
of the compression channels so that
the other can act as a filter, with the
filter’s centre frequency determined
by the front panel Frequency selector
knob setting. The VU meter displays
the master level output, while gain
reduction is shown on the LED meters.
The PEQ505 is a 5-band parametric
equaliser and each of its identical
channels feature continuously variable
level, frequency, and bandwidth
controls, an On/Off switch,
and a switch for selecting the channel’s frequency
operation range. The Master output includes a level
control, bypass switch, and an LED level meter with
peak indicator.
The Phase Box is a phase manipulation tool. The
phase can be manipulated by up to 180° with the
front panel rotary encoder. Bypass,
Low-Cut Filter, and Phase Reverse
switches are provided along with
Output level adjustment and VU
metering. The Pre-Z mic
preamp has 80dB of gain with
variable input impedance. HP
and LP filters offer additional
control and signal shaping
choices while LME49720
Op-Amps ensure low noise
and wide dynamic range.
The Tube Box is a singleslot 500-Series microphone preamp that
features a Class-A tube preamp, switchable
Phantom, phase invert, -20dB pad, and an
in-line optical compressor.
SM Pro offers a range of
500-Series racks, ranging from
the JuiceRack 1 (single-slot
Spotlight: Maag Audio
Maag Audio’s EQ2 is a 2-band EQ. It features Maag’s Air Band (shelf
boost from 2.5-40kHz) and a Low Mid Frequency bell boost from
Sub to 1.4kHz with tight and wide curves and an input attenuation
control providing -12.5dB of attenuation. The EQ2’s Air Band boasts
an additional 15kHz frequency selection.
The EQ4 is a one-channel 6-band equaliser with Air Band. EQ
adjustments are obtained with minimal phase shift and detented
controls allow for easily recallable settings. The PREQ4 is a onechannel microphone preamplifier with Air Band. Features include
65dB adjustable gain, phase reverse capability, 70Hz HP filter, +48V
phantom power, and -20dB pad.
Rupert Neve Designs
Daking’s Mic Pre 500 single-channel microphone/instrument
preamplifier module is derived from the
company’s Mic Pre One freestanding unit. The
preamp has switchable phase, 20dB mic input
pad, +48V phantom power, and a selectable 1/4inch line/Hi-Z instrument input. Like the Mic Pre
One, the Mic Pre 500 shares the gain structure
and Class-A, fully-discrete transistor circuitry
design of Daking’s Mic Pre IV. The front panel
controls include a variable HP filter (0-200Hz)
and continuously variable input gain. It also
includes an eight-segment tricolour LED with
simultaneous VU and Peak.
The Comp 500 is an easy-touse VCA compressor/limiter
module that has been designed
to perform and sound similar to the FET circuitry
found in Daking’s other compressor products,
even though it uses a VCA. Compression is set
with one knob, ranging from Less to More and
Release time is switchable between Fast (0.5ms)
and Auto — the Auto setting engages a dual time
constant. Attack can be switched between Fast
(1ms) and Slow (16ms), while Ratio is switchable
between Compressor and Limiter modes, setting
a 3:1 or 15:1 ratio. There is also a hard-wire Bypass
switch. A Stereo switch is provided that allows up
to six units to be linked. The eight-segment meter
is selectable between gain reduction or output levels and offers
VU ballistics with a floating peak.
Based on the Portico 5017 Mobile Pre, the 517
is a transformer-coupled preamp, compressor,
and DI with Vari-Phase — used to adjust phase
incrementally, Silk — reduces negative feedback
and adjusts the frequency spectrum to provide a
very sweet and musical performance — and DI/
mic blending capabilities. The 511 Mic Pre with Silk
incorporates the preamp circuitry from the 517, the
sweepable HP filter from the Portico 5012 Duo Mic Preamp, and
a variable Silk circuit from the Portico II Channel. The 511 can be
used for mic or line sources and has a polarity
reverse switch and a 12dB/octave swept HP
filter, while the Silk Red mode can be engaged
to add thickness and sparkle in the high end as
the Texture level is increased.
The 542 Tape Emulator is a follow-up to the
Portico 5042 Tape Emulator and delivers a
simulation of classic tape sound through the
inclusion of tape drive circuitry. The True Tape
drive circuit works by feeding a tiny magnetic record head, which,
in turn, is coupled to a correctly-equalised replay amplifier. As the
voltage rises on the record head, saturation increases, and a softclip circuit engages at higher levels to round off peak transients.
The sound of the tape circuit can be further modified with
selectable 15 and 30ips modes and a pre/post-tape blend control.
The 543 is a mono compressor-limiter with feedforward/feed-back modes, Peak/RMS detection,
and a built-in sidechain HP filter. It has individually
controllable threshold, attack, release, makeup
gain, ratio, sidechain HPF, Feed-forward/Feedback selection, and Peak/RMS detection modes.
With the compressor inactive, the 543 may be
used as a transformer-coupled, highperformance line amplifier. Two 543s
may be linked for stereo operation. The 551
Inductor EQ is designed by Rupert Neve. Featuring
three bands of EQ inspired by his most prized
vintage designs it has custom-wound inductors,
transformers, and Class-A gain blocks.
RND re-entered the proprietary modular
processing fray with its Shelford Series — named after
Little Shelford, near Cambridge, UK, where Rupert
Neve crafted a series of preamplifier and equaliser
designs. The 5051 EQ/Compressor combines a classic
3-band EQ based on Rupert’s vintage designs with
the power and flexibility of the Portico II compressor,
while the 5052 echoes the simple and definitive 1073
feature set with a vertically-orientated microphone
preamplifier, HP filter, and 3-band inductor EQ, also
incorporating modern capabilities like the variable Silk/Texture
control from the Portico II series and simultaneous pre/post ‘tape’
operation. His first fully-discrete mixing design in more than 30
years, the 5051 and 5052 may also be fitted into any of three available
vertical racks for standalone usage.
Warm Audio
power source for operating one module)
to the JuiceRack 8 (19-inch rack-mount
power source designed to house eight).
JuiceBlock 3 is a portable power block
designed to house three modules.
Eventide’s DDL-500 is a digital delay that
features 10 seconds of delay at 192kHz
and a design that keeps the amount of
digital circuitry to the minimum. Soft
saturation clipping, LP filter, feedback,
insert loop, relay bypass, and +20dB boost
are all analogue. Delay time can be varied
manually by connecting an LFO to the
remote input to allow short delays to be
used for comb filter or flanging effects. The
DDL-500 is also capable of extremely long
delays (up to 160s at 16kHz) to allowing
long passages to be captured for looping.
The WA12 500 Discrete mic pre uses customdesigned Cinemag input and output transformers.
Other features include 71dB of gain, a Tone button
(to switch the input impedance from 600Ohm to
150Ohm and change the tone of the mic and Hi-Z
inputs), 48V phantom, 20dB pad, and a 2MOhm
true Hi-Z front panel input (to send the instrument
signal through the entire circuit, including Cinemag
transformers and the discrete amplifier).
Audio Maintenance Limited
The AML 54F50 is a Class-A compressor and limiter module that
occupies three slots in a 500-Series rack. Populated with Carnhill
transformers, this British-built module offers make up gain
of 0-20dB in 2dB steps; compression ratio of 1.5:1, 2:1, 3:1, 4:1,
and 6:1; dual attack speeds (100µs and 5ms); recovery release
times of 400ms, 800ms, 1.6s, and Auto; and threshold settings
from 4-12dBu (in 1dB steps). AML offers pairs of 54F50s in a dual
racked unit with a mono stereo switch or in a 10-slot rack with a
mono switch.
resolution July/August 2014
Inward Connections
LaChapell Audio
Grace Design
T he Inward Conne c tions Magnum
500-Series Preamp uses two new VF-600
discrete amp blocks instead of the standard
SPA-690 to produce a much warmer
sounding response when compared to its
discontinued MPD-500 predecessor. The
unit has phantom power, phase reverse,
-20dB pad, Hi-Z low level instrument line
input, 12-position rotary trim (5dB per step),
three high-pass filter switches, an output
level rotary control, and balanced input and
output transformers.
The Brat is a 4-band parametric equaliser
also using VF-600 discrete amp blocks for warmth and definition.
It features High Band (sweepable from 1.2-25kHz with peak/shelf
select switch), Mid High Band (sweepable from 300Hz-7kHz), Mid
Lo Band (sweepable from 80Hz-1.6kHz), and Lo Band (sweepable
from 20Hz-300Hz with a peak/shelf select switch) with +/-12dB
cut and boost level for all bands to provide the shaping tools to
solve any demanding EQ application. Again, using VF-600 alldiscrete amp blocks, Inward Connections claims that The Brute
compressor/limiter is well suited to obtaining a ‘high-end’ vocal
sound. Its Optocell gain reduction circuitry is identical to the
renowned TSL-3 Vac-Rac tube limiter.
The Model 583E is a vacuum tube
microphone preamplifier with EQ.
It features the same amplifier stage
found on LaChapell Audio’s 583S
vacuum tube preamp, including the
Jensen JT-115k input transformer
coupled with a transformerless 3-band
EQ section with
co nt r o l s a n d
settings of
+/-8dB. The EQ can be run as an integrated
EQ serving the preamp as its own
autonomous module where both units
run independently. Like its counterpart
found on the Model 583E, the Model
503 EQ offers low distortion and minimal
phase deviation. It includes several features
not found on the Model 583E, including
increased cut/boost range (+/-12dB); LP filter (5kHz and 10kHz);
HP filter (50Hz and 150Hz); and +/1 trim gain stage.
Grace Design’s m502 is a compressor the
heart of which is an optical attenuator that
provides a wide range of dynamic control
yet remains neutral, open, and musical. It
includes input and output level, threshold,
attack, release, ratio, and make up gain
controls alongside balanced inputs and
outputs (with parallel XLR and 1/4-inch TRS
connectors) and a 1/4-inch TRS jack for stereo
link or sidechain input (including connectivity
for the Radial Workhorse bus feed). 10-segment LED gain
reduction meters make for easy reading and Grace Design offers
a five-year transferrable warranty on parts and labour.
Purple Audio
Cans II is a discrete stereo headphone amp and control room
preamplifier. It uses a KDJ3 Op-Amp for mono and a KDJ5
Op-Amp for its output. Features include a 10kOhm balanced
input, 15dBu gain, individual channel cuts, channel swap, channel
sum to mono, and precision matched stereo control. Cans II ships
with an XLRF to XLRF adaptor for stereo input.
Moiyn is an all-discrete 8-channel summing amp that only
works in the ninth slot in Purple Audio’s Sweet Ten 10-slot
500-Series rack. When a Moiyn is installed into that ninth slot,
slots 1 to 8 become input modules to the Moiyn itself. While
using the Moiyn to sum the outputs of the modules in slots 1 to
8, users can still route the output XLRs of slots 1 to 8 to a DAW or
tape machine. The inputs for slot 9 serves as a stereo input to the
Moiyn mix bus for cascading multiple mixers — for example, one
Sweet Ten loaded with a Moiyn can be used to handle a drum
mix and cascaded into a second Sweet Ten loaded with a Moiyn
to handle the whole mix as a fully discrete 16-channel summing
mixer with a combination of almost any 500-Series modules as
the channel modules.
Lindell Audio
The Weiss A1 is a microphone/
line preamplifier with a de-esser.
The sidechain of the de-esser
uses DSP enabling the use of
a very low noise element. Two
modules can be sidechain linked
for stereo operation. The A1 has
a transformer-balanced, widelevel range input with a 24dB
pad for line level sensitivity. The
input gain (15dB-60dB) is set with
a 16-position switch. Also included is a LP filter and phantom
power. The output is transformer balanced and has an additional
potentiometer to set the output level independently from the
levels that the de-esser is running at. The de-esser section uses
a bandpass filter to split the audio band. The bandpass filter
parameters are the centre frequency and the Q. The Threshold
parameter defines the sensitivity of the de-esser sidechain and
a few attack and release times and ratios can be selected via DIP
switches on the bottom of the unit.
Lindell Audio has three 500-Series modules. The PEX-500 is a one
channel transformer coupled passive Pultec EQ in an all-discrete
design based on the 990 amplifier. It has transformer-coupled
balanced inputs and balanced outputs; 15dB of gain; 3-step
switched LF boost at 30Hz, 60Hz, and 100Hz; HF boost at 6kHz,
10kHz, and 16kHz; and HF attenuation at 10kHz, 15kHz, and
20kHz. It also has true hardwire EQ bypass.
The 6X-500 is a one channel transformer coupled mic
preamplifier and passive 2-band Pultec equaliser. It offers 80dB
of gain with switched LF boost at 30Hz, 60Hz, and 100Hz, and
HF boost at 6kHz, 10kHz, and 16kHz. High boost bandwidth is
selectable on the PCB and there’s polarity reverse, 48V phantom
power and 5-LED VU metering.
The 7X-5000 is a one channel compressor/limiter and is what
Lindell describes as its take on the ‘1176 sound’. It’s a FET design
that incorporates a High Pass Sidechain Filter and a Mix knob
to mix between the dry and wet signal. It has 3-step switched
Attack times, Release times, High Pass Sidechain Filter (Off,
100Hz, 300Hz), and Ratio (4:1, 12:1, 100:1 ‘all in’). It has transformerbalanced output and a 20-LED gain reduction meter.
July/August 2014
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Radial Engineering
Radial’s Tank Driver module enables the
user to use the spring reverb in a guitar
amplifier and bring this effect into a
recording system. It features a wet dry
mix to balance the signal and shimmer
and boom controls to add top-end or
extra boom to the tone. For older reverbs
that may be less sensitive,
a drive switch increases
the output to compensate. The Tossover module
enables users to divide the frequency bands of an
audio signal to separately process lows and highs
or combine the two in series to create a band-pass
filter. The front panel sports one set of controls
focused on the mid and high frequencies, while
the other separates the mid and bass frequencies so
each can be processed individually. The frequency
knob lets users adjust the cut-off point and the
amplitude knob permits adjustment of the signal
level. To intensify the effect, each frequency divider is equipped
with a three-position filter that may be set with a 12, 18, or 24dB
per octave slope.
The Submix 4x1 mixer module has four frontmounted 1/4-inch input connectors with individual
level controls. Unlike a traditional mixer that requires
a separate input pad and level control, the Submix
employs Radial’s dual-gang Accustate input circuit
that lets you adjust sensitivity with gain. The mixer
has a virtual-earth mix bus design that enables it to
be cascaded without adding noise to create larger
The ChainDrive is an audio distribution module
that accepts a balanced or unbalanced source and distributes
the signal to four front-panel 1/4-inch TRS outputs with four front
panel level controls. The ChainDrive can also distribute a stereo
programme using TRS connectors following the tip-left, ringright, sleeve-ground convention. Once connected, ChainDrive
lets you create multiband compression, feeding several guitar
amps and effects simultaneously, or taking a stereo programme
and sending it to various digital processors, dynamic controllers,
and effects at the same time.
The PreComp 500-Series channel strip begins
with a preamp equipped with Radial’s Accustate
gain control that simultaneously sets the output
and sensitivity to maximise signal-to-noise. A
compressor follows with adjustable threshold,
compression ratio, and make
up gain control that transitions
from soft-knee to hard knee as
compression increases. A slowfast switch makes it easy to set
the PreComp for percussive
instruments or smoother tracks,
such as vocals.
The PreMax channel strip has a low-noise
Op-Amp input coupled with Radial’s Accustate
gain control. The preamp feeds a 3-band
shelving EQ and there’s also an HP filter, Phantom
power, and polarity reverse. The PhazeQ phase
adjustment module also works as a phase cancelling device
and summing equaliser. It enables you to phase-align two
signals, such as on a snare when using top and bottom mics
or when combining a direct feed with a room mic. With phase
summing, you can boost frequencies to create effects. PhazeQ
has discrete Class-A electronics and a variable phase control
shifts the incoming signal from 0° to 180° and then extends the
effect to 360° using a polarity invert switch. The blend control is
set to 100% wet when the PhazeQ is used in tandem with another
track. When used by itself, the blend is rotated counterclockwise
to set the desired wet-dry signal mix. A variable LP filter allows
the engineer to dial out high frequencies thereby only applying
phase cancellation to the bottom end.
Spotlight: JDK Audio
JDK Audio is a technology brand, developed and engineered by API out of a desire to use newer
technology that does not comfortably fit into the API product mix. The V10 is a single-channel mic
preamp sharing circuitry with a single channel of the R20 mic preamp. As such, it has 54dB of mic-level
gain, 45dB of instrument-level gain, padding, phantom power, and phase inversion. The V12 is a singlechannel compressor in 500-Series format sharing circuitry with a single channel of the R22 compressor
(itself a replica of the inline compressor on ATI Paragon consoles). It offers the patented Thrust circuit
that preserves high-frequency content even under aggressive compression settings and is paired with
threshold, ratio, knee, and gain make up controls.
The Q3 is a 3-band induction coil
EQ module. Described as ‘sweet
sounding’ it features a top-end
boost circuit; a mid-range cut
circuit; a bass boost circuit; and a
gain make-up control to offset the
typical signal loss that occurs when
using passive EQ designs. Each
of the three bands
employ a 12-position
Grayhill switch with a
different preset curve at each position. The Q4 is
a 100% discrete state-variable Class-A parametric
equaliser. As a line level device, it has four EQ
bands with fixed low and high frequency shelving
at 100Hz and 10kHz, plus two semi-parametric
mid bands that span between 300Hz-2.4kHz and
1-12kHz. Each mid band is also equipped with a
choice of wide or narrow Q and all frequencies
have 12dB of boost or cut.
Radial’s range of power racks extends beyond
the standard Workhorse, to include the standalone WR-8
Workhorse, an 8-slot 500-Series mixer. Individual XLR inputs and
outputs are complemented by parallel 1/4-inch TRS connectors
and 25-pin D-subs. The PowerStrip is a single-space 500-Series
power supply
designed to house
t h r e e 5 0 0 -S e r i e s
compatible modules.
It is equipped with XLR I-Os and 1/4inch TRS connectors. These can be
used as ‘multi’ outputs or for crosspatching purposes. Once modules are
inserted, a ‘feed’ switch immediately
sends the output from the first slot into
the second and then to the third, making
it easy to create the ultimate channel strip by
combining modules. The Cube is a 500-Series desktop power
supply designed to house three 500-Series modules. Topping
the power racks range is the Powerhouse, a 10-slot power rack.
It includes a Feed function and stereo link. Each channel slot
is equipped with separate XLR I-O with parallel 1/4-inch TRS
connectors for splitting the signal or acting as a patchbay. The
Powerhouse is equipped with Omniport 1/4-inch TRS that
accommodates special functions on 500-Series modules.
resolution Millennia Media
Millennia Media’s AD-596 A-DC is
based on the AD-R96 design, a feature
of which is the company’s proprietary
True-Lock-Clock performance with
an external clock. Its performance is
indistinguishable between internal
and external clock. Analogue inputs
and digital AES outputs are handled by
DB-25 connectors.
The HV-35 microphone preamplifier is
based on Millennia’s HV-3 Series and has
front panel instrument input, DC coupled ribbon mic switch with
10dB gain boost setting, 80Hz roll-off filter, 48V phantom power,
15dB pad, polarity flip, and continuously variable gain control.
The HV-37 is a pair of 500 series HV-35 preamp cards housed in a
1U rack with an onboard universal power supply. The rear panel
has XLR mic inputs and XLR balanced line outs. It can be powered
directly by mains voltages between 100V and 240V.
Using the same circuitry as Neve’s 88R console,
the 88RLB also includes new features such as
REGenerate and Direct Injection. The 88RLB is a
Class A/B amplifier design with its own special
transformer at the input stage and with an
electronically balanced output stage.
The 1073LB 500-Series mono mic preamp module
retains the sonic characteristics of
its original predecessor by using
the same architecture, matching
components, and original handwound transformers. With new
features like a fine Trim control,
switchable microphone input
impedance, signal presence LED,
intelligent protected switching of
front combi-XLR input connector,
and Neve’s Audio Processing Insert
design, the 1073LB expands on the
original Class-A design.
The 1073LBEQ provides a Neve 1073 EQ circuit,
using the same EQ design as the classic 1073
module. A Line level input feeds an electronically
balanced EQ circuit with three bands of adjustable
EQ and a High Pass filter, which can be switched in/
out. The output is also an electronically balanced
Line level output.
The Neve 2264ALB is a recreation of the
2264A limiter/compressor. It uses hand-wound
transformers to the original specs and adds a Slow
Attack switch that changes the attack time to 12ms.
Like the 1073LBEQ, it incorporates Neve’s Audio
Processing Insert design, allowing it to be inserted
between the input and output stages of a 1073LB
July/August 2014
CharterOak Acoustics
CharterOak’s K500 Ultra Parametric
3-Band Equaliser claims high headroom,
low distortion, and three ultra wide
bands. The Low Band centre frequency
sweeps 20Hz-500Hz, the constantly
variable Mid sweeps 500Hz-10kHz,
High Band sweeps 800Hz-20kHz, and
the bandwidth sweeps 0.50-2 octaves
in all three Bands. Additionally, there
are Bell and Shelf selection switches in high and low bands and
a ‘divide by 10’ switch in the Mid Band. There’s +/-12dB of gain in
2dB steps via 11-position rotary switches and a -24dB cut selection
on each band. High Pass Filter is -10dB@20kHz and Low Pass Filter
is -10dB@20kHz.
Ocean Audio
Safe Sound Audio
The Red Series mic preamp has
returned in the compact form of the
Red 1 500 Series Mic Pre. The module
is made in England and uses the same
circuit design and components as the
original, the same Lundahl LL1538
input transformer and custom Carnhill
output transformer, Grayhill goldplated gain switch with a gain range
of 66dB, switchable phantom power,
polarity invert, and a backlit VU meter
with calibration.
The 521 ZDT is Earthworks’ first 500-Series
module. Based on the ZDT preamp technology
designed by David Blackmer, the 521 ZDT
provides a ‘wire with gain’ option to the rack.
The solid state ZDT 521 has switchable phantom
power, polarity invert, and peak amplitude clip
detection. The transformerless output stage
will drive long cable runs without loss. Gain is
switchable from 5dB-60dB in 5dB steps.
There are currently six 500-Series modules in the Ocean Audio
product line-up and also a range of consoles — called The Ark
— that can be loaded with 500-Series modules. The 500 MicPre
one is a mic/line preamp module with additional Hi-Z/line input
on the front panel. The MicPre two is a transistor front-ended
mic/line preamp module with additional Hi-Z/line input on the
front panel. The 500 EQ one is a classic design 4-band equaliser
module with 4-band sweep and Malcolm Toft Signature Sound.
The 500 EQ two is a classic design 4-band equaliser module with
2-band sweep and Malcolm Toft Signature Sound.
Ocean Audio Mix modules turn a 500-Series rack into a modular
mixer. Use one 500 O/P Mix Master module with as many 500 I/P
Mix Input modules as the rack will hold to create a multichannel
mixer with EQ and aux sends per channel.
July/August 2014
Originally designed for the Olympic Studios
console by Dick Swettenham with guidance
from engineer Keith Grant, the A9052 EQ is
available. It provides extremely high and low
shelving bands as well as a two-position HP filter.
An addition to the original three-transistor make
up gain stage is a Class-A transistor output stage
capable of driving the most demanding of loads.
Also included is a step-down input transformer
and step-up output transformer that provide
6dB greater than the 500-Series voltage rails
normally allow.
The Realios TLCompressor combines highquality electronically-balanced audio elements
with a tungsten lamp as a gain reduction element to provide
smooth, artefact-free, soft-knee levelling. Features include
stepped Input (-15 to +22.5dB gain in 2.5dB steps) and Output
(-5 to +22.5dB gain in 2.5dB steps) attenuators, hard Bypass,
Threshold indicator lamp, and balanced input and output.
Safe Sound Audio’s Stereo Toolbox
is a stereo bus compressor capable
of processing audio in left/right or
mid/side. A stereo width control,
sweepable from mono through
stereo to extra wide, is available in
all modes of operation independent
of whether the user is processing in
LR or MS. The unit accepts balanced
stereo and delivers transformer
balanced outputs at levels up to
+28dBu. It is based on Safe Sound’s
‘dynamic tracking’ circuitry, which allows the attack and release
times to be dynamically modified by analogue processing to
track the dynamic content of the audio. The unit features a
sweepable HP filter that can be selected to operate during LR or
MS compression in the mono sidechain to control low frequency
pumping, or it can be switched to operate in the sidechain to
remove low end boom.
Serpent Audio
Serpent Audio’s SB4001 500-Series
stereo bus compressor has quad VCAs,
six ratios, 10 attack times, high pass/
boost/slope sidechain filters, wet/dry
blend control,
external (key)
input, stepped
release settings
and classic and
alternate auto release. There’s also a
Grind Mode for valve-style harmonic
drive. The Chimera is billed as a faithful
replication of the classic LA-3A design
featuring all-discrete circuit design, Class-AB transistor output,
true T4B optical cell, and transformer-balanced input and output.
Atlas Pro Audio
APA’s Leviathan compressor is inspired by the LA-3A and LA-2A’s
‘set and forget’ style programme-dependent compression with
its Vintage auto mode. As a discrete Class-A single-ended design
with iron core transformers on input and output, features include
variable attack, release, ratio, and Punch low frequency sidechain.
It can be closely stereo matched and stereo linked.
Tonelux Designs
Tonelux Designs’ MP5A is a discrete mic
preamp with Direct Input on the front panel.
This is transformer coupled and has a 20dB
Pad switch that affects both the mic and
direct input, a 48V phantom switch, and a
Polarity (phase) switch. The Combo XLR/
Direct input is for use with Hi-Z instruments.
The Tilt control works with the Mic input
and Direct input has its own Tilt EQ In
switch. When turned up, the tilt control has
a 0-6dB boost on the high end while cutting the low end by the
same amount. If it is turned down, the tilt will boost the low end
up to 6dB and cut the high end up to 6dB. Included with the
MP5A is the ability to PFL the output to an external preamplifier
or to the mixer/master section for previewing the signal directly
off the mic pre output.
The EQ5P is a discrete parametric equaliser.
Its front panel does not have a dedicated Q
control, but Q control is in relation to the
Boost and Cut controls, using a Constant
Energy Curve (or Proportional Q) to keep the
bandwidth wider at lower boost or cut levels
and narrower at higher or boost or cut levels.
The high frequency control has a shelving
button instead of a peak button. With 4 bands
of controls, each of the lower ones have
slightly different frequencies, allowing the
lower band to go to 16Hz, while the upper 2 bands are identical.
The TX5C is designed to address complex compression issues.
Its ability to handle in-module parallel mixing of the dry and
compressed signals means that users can sidechain an instrument
with itself to come up with a blend of the original and compressed
signal. The TX5C uses a proprietary all-discrete TX-240 Op-Amp
and all-discrete TX-260 output stage together with a TX-280
transformer. It includes the ability to fade between feed-back
and feed-forward compression using the Type control. The TX5C
has the ability to over-compress with the Ratio control causing
the compressor to reduce the gain at a higher ratio than the
gain being fed into it. The Ratio control allows the compressor
to compress an increase in signal of 10dB with a gain reduction
of up to -8dB. By inserting a Tilt control into the sidechain of the
RMS detector, users can increase the highs and decrease the lows
going into the RMS detector.
Tonelux also
the V4 Roadster,
a self-powered
racking system
that can power
up to eight modules with the X4 Expander.
Roger Schult
The V2350 line amplifier module is matched with
the API 500-Series and can be integrated into any
configuration. To provide for fast settings, the
V2350 is equipped with a central mode 11-step
switch with which the source selection can be
made and amplification adjusted in 10dB steps.
A separate 41-step level control allows additional
fine adjustment to be made with 0.25dB
resolution. The V2350a is a low-Z-matching
amplifier module for a wide range of signal
sources with low impedance. A continuous
impedance potentiometer allows adjustment
of signal sources between 10Ohm to 2.5kOhm.
The impedance pot works logarithmically and
its impact can be increased by a factor of four up
to 10kOhm. Conversely, the V2350b is a Hi-Z-matching amplifier
module for a wide range of signal sources with high impedance.
Spotlight: Crane Song
The Crane Song Falcon is a valve compressor and has three attack and three release settings,
hard and soft knee choices for compression or limiting, two different audio path sounds, wetdry mixing for parallel compression and can be linked. The audio path colour is changed by
modifying the tube circuit for negative feedback while the optical-like quality of the compressor
adds more versatility.
Syren is a classic sounding tube preamp built using a dual triode circuit with a 12AX7 tube. It
features a dual gain stage circuit and allows overdrive effects. A switch selectable Hi-Z input is
included. The low cut filter is at 90Hz and is 24dB/octave. The pad has -15dB and -25dB settings to
allow a wide input range of signals.
Valley People
The Guillotine is a Digitally-Controlled Analogue
High/Low Pass Filter module. Using a 12dB/
octave filter, it provides a means of returning to
exact settings. The Guillotine has 32 selectable
frequencies per band and provides visual
feedback for the high (15Hz-1.4kHz) and low
(28kHz-450Hz) bands using cascading LEDs —
32 for each band.
The Dyna-mite in its peak limit mode is a fast limiter that does
not ‘squash’ the programme as it can respond to transients in
around 6ms, allowing some of the fast rising waveforms to pass
through. There is gain recovery coupling in the control, so it
works as a high ratio compressor when the threshold is set below
0dB. Thanks to an auto-release circuit that prevents the release
circuit from interfering with the attack portion of the control
waveform, the Dyna-mite also works as an expander and gate.
The output circuitry is servo balanced and capable of driving
600Ohm into +24dB.
Shadow Hills
The Shadow Hills Dual Vandergraph
is a direct descendant of the Shadow
Hills Mastering Compressor. This
stereo compressor’s discrete audio
path is Class-A and features Shadow
Hills’ custom Iron Transformers. The
Dual Vandergraph’s Compression
and Output controls are Swiss-made,
24-position attenuators. The Ratio
switch selects between 1.2:1, 2.5:1, 4:1,
and 8:1. In addition to changing ratios,
each selection changes preset attack and recover times. The
Sidechain Filter Matrix controls the frequency sensitivity of the
sidechain with positions for 90Hz, 150Hz, 250Hz, and Bandpass.
The 535 Program EQ provides basic 2-band
EQ with two frequency choices per band.
Based on the active version of the Baxandall
circuit, the 535 includes an amplifier for each
band to avoid interaction. The slopes of the
535 are of the very gentle shelving variety.
A maximum of 4dB/octave is achieved at
full boost/cut. The 541 Optical compressor
is a feedback-style compressor, designed
for smooth, unobtrusive gain reduction. It
uses Silonex optocouplers for gain reduction
and subtractive metering. Its control set is
minimal, comprising a ten-segment LED
gain reduction meter, a threshold control
operating in a dbx-style counterclockwise
direction with an arbitrary
orientation, and make
up gain. The 545 Optical
Disrupter is an optical
compressor that creates an asymmetrical
waveform as it compresses low frequencies,
resulting in smooth, second-order harmonic
distortion without clipping and associated
harshness. The 570 Mic Preamp is a simple
design featuring a Lundahl LL1576 input
transformer and a continuously variable gain pot (ranging from
28-65dB), 20dB pad, phantom power switch with LED, and tenstep LED peak meter.
resolution Moog Music
The Ladder is a Dynamic Transistor
Ladder Filter that is based on Bob Moog’s
original ladder filter designs. It sports a
smooth sounding, all-analogue LP and
HP filter section and variable Attack and
Release controls allow the envelope to
be opened and closed. The Amount
control in Positive or Negative mode
allows for mid to extreme sound shaping
and manipulation. There’s a Resonance
control. The 2-Pole/4-Pole switch allows
users to select how aggressive the filter
slope is. 2-Pole is equal to 12dB/octave
and 4-Pole is 24dB/octave.
The Moog Analog Delay is a MIDI-synchable module with
an analogue signal path, front panel MIDI, and an assignable
Tap Tempo/CV jack. It offers between 35-800ms and also has a
6-Waveshape LFO that allows users to create time-based effects.
The LFO can be accessed via MIDI or the free VST/AU/RTAS Analog
Delay plug-in editor.
Alta Moda Audio
The successor to the AM-20 equaliser, the AM-25 is
a 4-band parametric equaliser module. It offers four
continuously variable and overlapping frequency
bands: shelving or peak/dip Low Band, continuously
variable from 20-120Hz; parametric Low Mid Band
with variable Q (65Hz-2kHz); parametric High Mid
Band with variable Q (1-7.5kHz); shelving High Band
with variable Q (4-20kHz).
Alta Moda’s first mic preamp,
the AM-30, is discrete Class-A
transformerless and can be smoothly
overdriven by increasing input level or gain,
The Gain control is an 11-position rotary
while the Output control is a continuous
fader with an additional 6dB of overall
boost. A direct input on 1/4-inch jack is
included. The Hippo is a high-performance bus compressor
based on VCA topology. It features attack, release, and ratio and
a six-position HPF on the sidechain while a six-position Warmth
control adds harmonic distortion to fatten tracks.
July/August 2014
Thermionic Culture
The Nightingale is the second of Thermionic Culture’s half-rack 4U
format units, the first being the Freebird 3-channel value EQ. It is
an all-valve affair with two ECC832 for mic amp/EQ, 6AQ8, 5965,
and 5726 in the compressor section. Two mic amps with a useful
valve EQ have their own outputs (XLR unbalanced) which can give
+20dBu. These can be combined or taken individually into a varimu compressor-based on The Phoenix stereo valve compressor,
but with a little more ‘attitude’. The compressor section has its own input (balanced XLR) which can
be selected instead of a feed from the mic amps, also an XLR balanced output capable of +25dBu.
Inside and
behind the rack
Not all modules and racks are created equal.
We talk to Radial Engineering president
PETER JANIS about the ins and the outs.
Standard Audio
The Standard Audio Stretch multiband compression unit is inspired by 70s and 80s tape noise
reduction units. The input signal is split into LF (20-110Hz), MF (110Hz-3kHz), HF3 (3-20kHz), and
HF9 (9-20kHz) frequency bands and then individually compressed with ratio, attack, and release
settings tailored to each frequency band. The Input control allows the user to set the gain structure
through the unit so that the desired amount of compression occurs while a post-mix circuit Output
level control allows the engineer to set the output level to DAW/tape without altering the mix
blend. A Filter/Compression pushbutton lets the user cycle continuously through seven different
filter combinations.
JLM Audio
The BA500 mic preamp module uses a discrete 99V Op-Amp for 60dB of gain
and an impedance control range from 200Hz-3kHz. It has a large white LEDbacklit 34mm VU meter for output level. The TG500 mic preamp module is a
two-FET, six-transistor Class-A design providing 75dB of gain. It is based on
early Neve, BBC, and EMI equipment with simple transistor stages that have
been redesigned to include additional features. The LA500 compressor is a
redesign of the LA-3A/LA-2A-type compressor with additional features, including 5:1 and 10:1 ratios
(in addition to 3:1) and sidechain HPF switching between flat, 100Hz, and 200Hz, so the low end can
be compressed or removed from the sidechain. A make-up level pot varies between 0-20dB of gain.
The FC500 Enhanced FET Compressor is a redesign of the 1176LN-type compressor with a fully
variable Ratio control (from 3:1 to 20:1) and sidechain HPF (from 10-100Hz). Compression linking is
possible with two or more FC500s using the link switch. The HPM500 is a six-channel headphone
mixer module that fits in the spare space next to the API Lunchbox power supply so no 500 slots
are wasted in the Lunchbox itself. Since there are 12 wires to solder to the back plane output XLRs,
an IDC plug that has to be removed from the power supply to the mixer car, and a short extension
cable plugged from the mixer to the power supply, it is recommended that the HPM500 is installed
by a technician.
Avedis Audio Electronics
The E27 is a 3-band equaliser module with nine
selectable frequencies per band. The all-discrete
design also boasts +/-16dB boost and cut using a continuously
variable potentiometer, pushbutton shelving option for low and high frequencies,
high headroom, and low noise. Jensen transformers couple the input and output. Custom machined
aluminium knobs adorn Gold-plated rotary switches. Avedis Audio also manufactures the R52, a dual
rack compatible with select Series-500 modules. It features an internally regulated power supply
with phantom power, a Link switch for connecting channels, and an LED power supply indicator.
JCF Audio
Aimed fairly and squarely at the front end of the recording chain, where broad
strokes of sound adjustment need to be made quickly, the JCF Audio More
‘n’ Less is a channel amplifier with mic (configurable as front only or front and
rear) and line (rear only) inputs. No switching is needed between these inputs.
It has an Output level control, single knob compression and simultaneous
make up gain function, a static boost equaliser — Top or Bottom and a
dynamic loss equaliser. A Cinemag steel 1:2 output transformer is used for floating output, isolation,
and drive, while a four-position pad optimises drive of the Cinemag mic input transformer.
JMK Audio
The JM-115C is a transformer-coupled VCA-based compressor using true RMS detection similar to
the dbx 160VU. Compression ratio starts at 1.25:1, rising to 20:1. The JM-120 is a dual Hi-Z input DI
preamp with one common (Jensen) transformer-balanced output. The Guitar input is specifically
designed for guitar input impedance, gain structure (maximum 48dB), bandwidth all optimised to
produce a clean and quiet signal. The Bass/Keyboard input is designed for the higher output of a
bass guitar or keyboard and optimised for bass.
July/August 2014
he 500 series is a modular system that enables the user to bring
together preamps, equalisers, dynamics and effects and combine
them to create unique sounds and push creativity during the
recording process. Each module fits inside one or two slots — two
slots being stereo — and then these are connected on the rear panel of
the power rack using standard XLR cables. The general intent is that the
modules work at +4dB line levels to facilitate inter-module connectivity.
Today’s 500 series format is a grandfathered ‘standard’ that originated
with several companies, including API, Aphex, and DBX. Over the years
API stuck with the format and more recently there has been enormous
growth in the number of manufacturers producing 500 series modules
and the racks to power them from. The enduring attraction of this modular
processing package is that it is compact, portable and allows the user to mix
and match modules and to be able to sample premium brand products in an
affordable way.
Lots of manufacturers make 500 racks, what operating
principles are they basing their racks on?
It seems that most companies that offer racks are offering variations on
the original API spec. In other words, they make a box with a bunch of
slots and then provide power via a 15-pin card edge connector following
the pin configuration that was originally set out by API. EDAC tends to be
the connector of choice as these have two conductive sides for improved
The powering of the racks seem to range from about 100 milliamps per
slot and up. As API set out the standard at 130 milliamps, this seems to be
the predominant format. The power supplies provide a shared pool of current
from which the user then determines which modules can be used. With the advent of power hungry tube devices and the demand for
vintage solid state devices to be moved into the 500 series format, it seems
that more power is beneficial as many of these devices were designed with
greater power availability than the original 500 series format. How did Radial do what is has with its 500 racks?
Radial started with the idea that a power rack could do a lot more if the
modules could be mixed and matched in series or in parallel. This prompted
us to incorporate a mixer in the Workhorse. We also thought that replacing
patch cables with feed switches could simplify setups and keep the rear patch
panel clear. We then took the position that the rear panel could actually work
as a patchbay if ¼-inch TRS cables could be incorporated. Finally, because
API had left a couple of pins free in its latest designs, we adopted them for the
Onmniport jack. This ‘module specific’ port enables a manufacturer to add
a feature such as an insert, key, instrument input or whatever, as an extra
function to their module without changing the original spec. Once we got things going, we then quickly discovered many ‘home-built’
modules are not necessarily built properly. During testing, in some cases,
they actually caught fire. So we added safety fuses that basically shut down
the racks should a fault occur. This not only protects the Radial Workhorse
power rack, but also protects modules and your home! After the Workhorse was completed, we then added various other rack
formats to suit different customer needs for 3, 6 and 10 spaces. resolution
How real are concerns that
certain racks do not generate
enough juice for power hungry
modules like valve modules?
When tubes are employed, the power
requirements increase to where 200
to 300 milliamps are required. One
merely checks the power supply for
available current and then adds up
the requirements to ensure you do not
exceed the available current.
We came up with a clever
workaround for the PowerTube
module that pulls current in form
alternating sides of the power supply
to reduce the demands when using several of
these tube preamps together in a rack. State the case for a ‘standard’ for the 500
series rack.
Another discovery was that there was no
clear standard. We spent months researching
older designs and could not find any clear
documentation that set a clear standard for size,
power, or pin configurations. We even found API
modules that did not fit inside their own racks.
You have to keep in mind that API has gone
through different ownerships since the 1970s
and old designs have been kept for legacy sake.
We contacted API for clarity and they suggested
that we send them our modules for testing to see
if they fit and would not cause problems. This is
the basis for their VPR alliance.
Anyone who has been in our business for any
length of time knows that the audio industry is
extremely slow at developing clear standards. We
have been in the digital world for over 30 years
and still today one digital console cannot always
speak to others. We felt the best solution would
be to suggest a free standard and we posted this
on our website. It includes mechanical designs,
electrical requirements and everything you need
to build a module.
Once the Whos-Doc specification was posted, we then
contacted the AES to let them know that we would be pleased
to support a new standard that all manufacturers could adopt.
A couple of the people from the standards committee have
contacted us and we are now waiting to hear of further
developments. Whether the AES adopts a higher or lower voltage
standard, we are prepared to support it as we believe this to be
the healthiest way forward. We believe that the end user should
be able to buy any brand of module, plug it into a rack and it
should work. If every manufacturer goes about optimising the
power racks for their own modules, the industry will never be
One of the most frustrating aspects of the ‘non-standard’ is
the way modules must be fit into place. Aligning the 15-pin
card edge connector is painful and can lead to electrical problems
if not inserted properly. To address the problem, we started by
adding a simple slide-in tray that aligns the card edge vertically.
Most recently, we tooled up the trays with special nylon inserts
that align the modules horizontally so that they slide into place
without fiddling around. This makes it easy to quickly plug
in modules and change the recording setup on the fly. Any
manufacturer who adopts the Whos-Doc standard will find that
their modules fit easily, which in turn will reduce service problems.
Set out a power consumption and
distribution model for a rack full of
typical modules.
Say you have a Radial PowerHouse 10-slot
rack with 1600 milliamps of current, this
gives you an average of 160 milliamps
per slot. If you have four tube preamps
that require 250 milliamps each, two EQs
that need 100 milliamps and a couple of
compressor that need 150 milliamps, you
add them up and you get 1500 milliamps of
required current — this leaves you with 100
milliamps of headroom. If you plug in six
tube preamps — at 250 milliamps each and
an EQ that needs 100 milliamps — you will
be at the threshold of 1600 milliamps which
means you may not enjoy the maximum
performance. It is probably a good idea to
leave some slots empty if you can so that you
have extra headroom.
How real are people’s concerns about the
power issues?
I suppose most racks will do a
reasonable job when it comes to
powering. We have been told by several
major manufacturers that the Radial
racks are the ones that are truly made
correctly. The real issue in our mind is
safety. When a console manufacturer
is creating a channel strip it is in full
control of all of the signals going in and
out. In the 500 world, you are guessing
and hoping that each of the modules are
properly constructed and safe. This is why
we go the extra mile by incorporating
electronic fuses in each channel. Should
a fault occur, the rack will power down
until the fault is removed and then
simply comes back to life.
What are the realistic power requirements of a 500 series rack
and what are they able to power?
The issue with powering is two-fold. On the one hand is the in-rush current
and on the other the actual powering of the modules. We have found some
companies whose products require excessive in-rush current to bring them
up. The workaround is sequencing the modules by plugging them in, one at
a time. A good electronic engineer can design a preamp, EQ or compressor
with less than 100 milliamps of current. With some attention, the in-rush
current can be reduced so that it does not exceed the power of the supply as the
capacitors charge. 40
What other limitations and
concerns are there about 500 Series
racks and modules?
The standard in itself is limiting. It is
designed around an analogue mono format,
so you cannot easily integrate stereo into a single
wide module. Also, because the standard originated
in the 1970s digital was never part of the design. So
developing a digital strategy is somewhat limiting.
In our view, the best way around this is to incorporate some
sort of digital I-O in the master section. This has recently been introduced by
Aphex in its new rack and we are looking at other methods of implementing
something similar. This would enable the user to go from a laptop computer to
the 500 series power rack and back in order to take advantage of the character
and creative approach that analogue brings to recording. n
resolution July/August 2014
AWA R D S 2014
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