A Technical Look at the Ruppert Musical Instruments Fig. 1

A Technical Look at the Ruppert Musical Instruments Fig. 1
Fig. 1 Gutshot
Fig. 5 Top view
A Technical Look at the Ruppert
Musical Instruments
Basswitch IQ DI Bass Preamp and DI
By: Tom Lees
The Basswitch IQ DI from Ruppert Musical Instruments is selfproclaimed as the bass player’s Swiss army knife. Well, after
trying for a short time, and even after consulting the manual, I
could not locate a bottle opener to pop open my… um…
beverage. I also could not locate a fork, serrated knife or a
toothpick. As such, I will not be packing the Basswitch IQ DI
with my camping gear.
Now, I have to admit that not every model of Swiss army knife
has the above utensils. However, every Swiss army knife does
have a few distinguishing traits. It is functional and
convenient… to the point of being a “must-have” accessory. So,
let’s see if the Basswitch IQ DI can pack enough wallop in the
functionality and convenience categories to truly be a must-have
accessory in the bass player’s gig bag.
Construction
For a pedal, we have a lot to talk about, so let’s get started with
the gratuitous gut shot of Fig. 1. Taking a look at the internal
construction, it is easy to conclude that the Basswitch IQ DI is a
well thought out and neatly assembled device. The jacks and
switches along the back and side panels are directly soldered to
the circuit board, which sits neatly in a rugged enclosure. The
potentiometers are coupled to the housing via a custom bracket.
The electrical components include a mix of surface mount
devices (e.g., resistors, operational amplifiers, etc.) and throughhole devices (e.g., the red boxed capacitors). All together, the
Basswitch IQ DI will likely serve as a dependable tool as long
as you want to keep the device in service.
There are few notable features, however, that are worth
particular attention. The Basswitch IQ DI accommodates power
supplies that range from 9-20 volt DC (regardless of polarity) or
AC. For any supplied voltage within its range, the internal
circuitry internally rectifies, filters and stabilizes the power to
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Fig. 2 Actuator button profile
18V DC internal working voltage. To test this out, I applied
power to the Basswitch IQ DI from variable bench power
supplies and from random adapters I pulled out of my spare
adapters bin. Regardless of adapter, the Basswitch IQ DI
powered up and performed consistently. I cannot understate how
much I appreciate this attention to detail.
The Basswitch IQ DI includes a true transformer isolated DI.
This is the silver “box” seen towards the lower right corner of
the circuit board in Fig. 1. Transformer isolation is critical for
eliminating ground hum and other noise when connecting your
gear to a mixing console.
Referring to Fig. 2 along with Fig. 1, instead of traditional
mechanical footswitches, the Basswitch IQ DI uses a switching
system that combines an external “actuator button” (this is the
thing that you stomp on – see Fig. 2) that operates an internal
switch that triggers a relay (these are the three black boxes, each
having a silver angled lever arm across the bottom of the circuit
board in Fig. 1). Although this system sounds more complicated
that a simple footswitch, the result is arguably superior to a
mechanical switch in three key areas. First, the actuator button
absorbs the load of the foot of the musician and transfers the
exerted force into the housing. This greatly reduces stress on the
actual switch components and circuit board. As the actuator
button depresses downward, a small force is used to pivot the
corresponding lever arm, which triggers a relay. The result is a
switching system that should not break down, even under the
most heavy footed of bass players. Second, because the
switching system uses relays for the actual internal switching,
each switch should be able to perform a few million switching
cycles before failure. Third, because the switching is performed
by a relay (having gold contacts), the switching noise is almost
negligible. There is no annoying “click” sound, which can be
distracting in certain performance environments.
Referring to Fig. 3, a side profile yields another view of the
actuator buttons, and also shows another cool feature of this
device. Situated in cooperation with the knobs is a riser feature.
This riser protects the knobs from unintended turning and
serves as a barrier to protect the knobs, e.g., from a large boot
or from someone inadvertently stepping on the device.
Fig. 3 Housing side profile
Fig. 4 Block diagram
Fig. 6 Bass response
Operation
One of the best ways to get a sense of how the Basswitch IQ DI
works is by taking a few minutes to familiarize yourself with
the schematic, which is included in the manual and is
reproduced herein as Fig. 4. The schematic should be read with
the unit in front of you so that you can compare the flow to the
input/output options found on the back and side panels of the
unit – see Fig. 5.
As a quick overview of the features, working right to left, first
across the back panel, the Basswitch IQ DI includes two inputs
(INST A and INST B), an impedance selector switch for the
first input (INST A), a line out, a tuner out, two loops including
a serial loop (SER LOOP) and a parallel loop (MIX Loop), and
a power input. The DI is on the side panel and includes a
balanced XLR output, as well as buttons for ground lift, pad
and pre/post EQ. The Basswitch IQ DI also boasts three
footswitches on the top panel which, from right to left include,
a first footswitch to control selection between two internal
channels (Channel A or Channel B); a middle footswitch to
control MUTE ON/OFF; and a third footswitch to control MIX
LOOP/BOOST ON/OFF. The top panel also features a number
of user controls, including a volume control, equalization
controls and boost and mix controls.
The Basswitch IQ DI has two internal channels, Channel A and
Channel B. Channel A has a user-selectable impedance option,
which is controlled by the impedance selector switch on the
back panel, followed by a preamp that is controlled by the
Volume knob. A tap of the signal is taken after the volume
control and before an equalization section to provide a nonequalized option for the DI. The signal then passes through a
four-band, semi-parametric equalizer that features bass, a user
variable low-mid band (user-adjustable gain and center
frequency), a user variable hi-mid band (user-adjustable gain
and center frequency) and treble controls. Channel B, by
comparison, is intended to provide a pure path that does not
include either a user adjustable gain or equalization. Thus, if
you are using both channels, any desired volume leveling must
be done using the volume knob of Channel A. Because of this,
the preamp of Channel A is configured to provide a range of
adjustments from cut to boost.
The routing scheme is deceptively flexible for such a simple
layout, so stay with me here. When an instrument is plugged
into the INST A jack, and INST B is left unconnected, the
signal at Input A is fed to both channels. The A/B footswitch
toggles between internal Channel A and internal Channel B.
Thus, two switchable settings can be applied to the same signal.
Fig. 7 Low Mid Response
The Volume control of Channel A controls the overall volume
by providing about 16dB of attenuation when turned off, to
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about 12.5dB of gain when turned to full on. Unity gain is just
between 12-1 o’clock. When switched to Channel B, I
measured a gain of about 0.9dB, so the output is not quite unity
gain.
When an instrument is plugged into INST B, the signal is
routed to Channel B only. Thus, if no instrument is plugged into
the INST A jack, the operation of the A/B footswitch will be
similar to a Mute when Channel A is selected. [I would
recommend that if you only have one cable, plug into the INST
A jack, as a Mute function is already provided by the middle
footswitch.] Otherwise, if you have two instruments that you
want plugged in at the same time, plug the instrument you want
volume and EQ control over, into the INST A jack, and the
instrument that you do not need volume and EQ control over,
into the INST B jack. Here, the A/B footswitch will select
between instruments.
Fig. 8 High-Mid Response
Keeping with the schematic, the tuner out is taken after the
Channel A and Channel B outputs. Here, the A/B footswitch
will select which channel is fed to the tuner. The Mute
footswitch controls a mute function, which is located just after
the Channel A and Channel B outputs. As such, muting the
device kills the signal to the DI, line out, serial effects loop and
parallel effects loop, but not the tuner.
The parallel loop is positioned just before the series loop and
after the Mute switch. The parallel circuit integrates a cool
boost feature. If the parallel loop is used, the Boost control can
be used to level shift the send to get an appropriate level to the
device inserted into the loop. If no device is plugged into the
Mix Loop Return jack, the Boost control can be used in
cooperation with the phase shift and mix controls to alter the
signal, e.g., to provide a switchable solo boost to the selected
channel.
The Channel A Tone Stack
The frequency response of the EQ section of Channel A is
illustrated in Figs. 6-9. Notably, the Bass control is a peaking
(bandpass) control, having a center just over 30Hz. The LowMid control provides a user-adjustable sweep from just under
100Hz to about 500Hz. As the user-selected center frequency
increases, the bandwidth also increases. The Mid-High control
provides user-adjustable sweep from around 800Hz to over
5kHz. Again, as the user-selected center frequency increases,
the bandwidth also increases. The High control is a fixed shelf
type control. By providing about +/- 18dB of control for each
EQ section, quite a bit of tone shaping is possible with this
equalizer.
Fig. 9 Treble Response
Fig. 10 Distortion Product Ratio
The technical data included in the manual for this device lists
the frequency range as 20Hz-100kHz, so I decided to put this to
the test. I ran a frequency response test from 10Hz to 80kHz
with all tone controls about noon and measured a frequency
response +/- 0.93 on Channel A (+/- 0.26 from 20 Hz - 20 kHz),
and +/- 0.7 on channel B (+/- 0.18 from 20 Hz - 20 kHz). For
those keeping track of scores at home, I would check this off in
the “awesome” category if you dig flat response devices.
Performance
The Basswitch IQ DI is capable of handling a wide range of
input levels in a clean manner. Referring to Fig. 10, a 1 Vrms,
1kHz signal produced exceptionally low distortion, with both
first and second harmonics almost 100dB down. Fig. 11 shows
a chart of THD+N as a function of input level. As this chart
Fig. 11 THD+N Ratio
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shows, for input signals up to about 5 Vrms, distortion remains
well below 1%, and is well below 0.01% for signal levels
between about 100 mVrms and about 4 Vrms. Moreover,
referring to Fig. 12, linearity is excellent over a range of input
signal levels. Here, linearity refers to the relationship of input to
output. I dialed in the output for about unity gain. As the chart
shows, the relationship of input to output is pretty much flat
until the input is overloaded, which happens pretty close to 5
Vrms. This is a healthy input signal and is likely well in excess
of what your instrument puts out under normal playing
conditions.
Fig. 12 Linearity
Fig. 13 Channel B Input 5.5 Vrms
However, the clean, linear nature of this device is not limitless.
Speaking of limitless, there is no limiter on this device, and
hitting the limit (rail) of this device is like driving into a brick
wall. Referring to Figs. 13-15, I pushed a 1kHz input signal into
Channel B and brought up the level to see how the Basswitch
IQ DI would handle an overload situation. At 5.5 Vrms in (Fig.
13), the device was cruising, outputting a 4.93 Vrms signal
(remember, Channel B is just under unity gain) at less than 0.5
% THD+N. By 5.6 Vrms in (Fig. 14), the output distortion
swiftly rose to 19.7% THD+N, with an ugly distortion in the
negative swinging peak. By the time the input reached 6 Vrms
(Fig. 15), distortion was measured at 73.15% THD+N, with
squaring of the peaks and a fold over of the negative going peak
into a square spike.
Curiously, the user-adjustable impedance of Channel A intrigued
me. The idea of having a high impedance of 10 Mohm for piezo
and other high-impedance devices seems like a great idea.
However, I measured 507 kOhm at the 1 MOhm setting, and
940 kOhm at the 10 Mohm setting, at 200 mVrms 1 kHz input.
The Channel B input fared better, measuring at 1.2 Mohm.
Conclusions
For many bass players, Basswitch IQ DI may just be a musthave accessory. The EQ is flexible, the routing and two
available loops provide options galore, the ability to convert the
parallel loop into a boost function is useful and practically
implemented, and the transformer isolated DI provides a full
featured routing to the mixer. The device cannot be run on
batteries. However, the flexible nature of the power supply
section allows the use of virtually any wall-wart that a typical
musician will have sitting around. I also really like the manual.
The manual is chock full of useful information and tips, and
presents the use of the device in an easy to read and follow
format.
Fig. 14 Channel B Input 5.6 Vrms
I do have two small issues. I love the idea of the footswitches.
However, as Fig. 2 illustrates, the button “caps” mushroom out
over the actuator stem providing a flat undercut. Moreover, the
spring that biases the button up is pretty thin. During use, I got
a thin cord caught under the switch, which prevented the button
to depress enough to trigger the device. Of course, I could feel
the switch not depress fully, and could visually see that the
device did not switch by the color of the indicator light. It was
an easy remedy to pull out the cord. Still, it was a nuisance.
Also, I found it interesting that I measured a higher input
impedance on Channel B than on Channel A, even with the
switch set to 10 MOhm. On the whole, though, the Basswitch
IQ DI is an impressive technical accomplishment.
Fig. 15 Channel B Input 6 Vrms
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Corrections for issue #8:
On the Quick Look review of
the Eden WTDI Direct
Box/Preamp, on page 11, we
incorrectly stated that it was
“Made in: USA.” The review
should have read, “Made in:
China.”
In the fEARful Phenomenon
article, the text on pages 57 and
58 should have been switched,
one for the other.
Manufacturer’s Response:
Jacques Ruppert, Ruppert
Musical Instruments
We would like to thank Tom
Lees for this detailed test that
confirms our own
measurements. On the very first
series of Basswitch IQ DI pedals,
both inputs have to be in use to
achieve correct impedance
values on channel A. For all
Basswitch pedals now on sale in
the US, this is no longer needed.
We have at the same time
improved the design of the
push buttons so that they work
smother, now. In our strive for
excellence in quality and
service, we offer all customers
that would have a problem with
their Basswitch in this area a
free upgrade and shipping back,
if they return us the pedal.
Roger Baer, Baer Amplification
As the mid driver is naturally
balanced very well in sensitivity
to the woofer, we felt that an LPad for the midrange wasn’t
worth the trade off of adding
extra circuitry to the crossover.
John Pirruccelloo, Lakland
With regard to the comments
about the DJ-5’s price point, we
believe that MAP (minimum
advertised price), a.k.a “street
price,” is much more
representative of the actual
price a customer will pay. Street
price for the DJ-5 is $1,349,
which is $350 less than an
American Standard Deluxe Jazz
V (street). I feel this puts us in a
slightly lower price point
category, which may change a
reader’s perception of value. I
sure wish the music industry
would let go of the MSRP game.
It can be somewhat confusing
for people!
The pickups in this bass are our
own design vintage-style
pickups, wound right here in our
Chicago shop with hand built
bobbins made from vintage
spec materials. The fact that
they don’t look like anything
special is by design, since our
aim was to offer a vintage spec,
high quality USA-made pickup
with class-leading tone.
With regard to the neck setup
analysis, we are constantly
reviewing our processes to
improve our products and the
issues you pointed out with
regards to the neck fit tolerance
and nut fit and finish are being
addressed! Just to brag a bit,
for the last three years,
Lakland’s return/repair
authorizations have been well
below 2%. All after-sale
customers are treated like
royalty! Regarding the treble
side neck pocket design and
“possible lateral instability,” I
can honestly say that this has
never been an issue since we
debuted this design in 1994.
Passive basses and shielding.
Since the introduction of our
first passive basses in the mid
1990s, Lakland’s position has
been that vintage basses from
the late ‘50s to ‘60s without
cavity shielding sounded livelier
than shielded versions, that to
our ears sounded considerably
duller. All Lakland passive
instruments default to this
vintage spec and achieve what
we feel is a superior tone.
However, Lakland will shield
passive models at no extra
charge upon special order or as
post sale support. It should be
noted that our vintage style
pickups are fully wax potted to
prevent micro phonics (in case
there is any confusion between
shielding and potting).
Gerald Marleaux, Marleaux
BassGuitars
We now use a different trussrod
than what was used in these
instruments. All of the basses
we build have a pre-tension in
the neck – when under string
tension, the trussrod needs no
power – so we have much more
than enough headroom in both
directions.
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