INSTRUCTIONS / INFORMATION

DUAL-CHAINED LIMITING AMPLIFIER
Key Features:
INSTRUCTIONS / INFORMATION
• 100% Class-A discrete signal path
• Chained compressors for more "squash"
• Two user-presets
• Ultra-fast “FET” response
• Massive gain of 75dB at zero compression
• Internal Attack & Release presets
• Studio-grade “discrete” preamplifier
• Low-noise electronics
• Selectable True, or Buffered, Bypass
• 50 hours life from single 9V / PP3 cell
• Optional external power (9-18V DC)
• Traditional Through-Hole PCB
Our goal was to reproduce the slide-guitar
tones first heard on Little Feat’s classic
album, "Dixie Chicken". The tone is clean
and transparent, with an almost infinite
shimmering-sustain.
For
many
this
represents the ultimate in slide-tone.
In the studio, the Little Feat tone was
achieved by daisy-chain-connecting two
Urei 1176 "FET" compressor channels. The
1176 has a fast response, unique character
and smooth compression. Chaining the
compressor sections allows the character to
be retained, whilst vastly increasing the
amount of compression. This level of
compression is generally referred to as
"Limiting" as the signal is maintained at a
consistent level.
Block Diagram (Compressor Section)
Our 1176-inspired Cali76 circuit forms the
backbone of the SlideRig – with two
identical Cali76 blocks being utilised in a
true, dual-chained, topology.
The unit features switch-able user-settings,
providing the user with separate rhythm
and lead presets. The most common
scenario being the use of a subtle
compression for quieter passages; and a
fuller compression, with a clean level boost,
for solo work.
A studio-grade 1960s-style preamp works as
an interface between the guitar and the
first compressor section. Just like the
compressor blocks, the preamp uses discrete
Class-A electronics for the purest tone
possible.
The pedal can be powered from a single 9V
battery, or from a 9V to 18V DC power
supply. A higher-voltage external supply
will increase the dynamic range of the unit
and permits the use of hotter input signals.
Overall, the sound will be cleaner,
especially at extreme settings.
Figure 1: Block Diagram of Compressor Section (Conceptually Simplified).
Input/Comp Control
Bypass Mode (Internal Selection)
The SlideRig features a very nice studio-grade input
preamplifier. This works as an interface between the guitar
and the compressor sections. In exactly the same way a
studio-engineer will first amplify a dry guitar signal before
applying additional processing.
The bypass mode can be selected internally by changing the
positions of four internal jumper-connectors.
The "INPUT/COMP" control allows the user to vary the gain of
this preamplifier. Turning this control clockwise increases the
overall gain of the pedal. This also increases the amount of
compression. The guitar will become increasingly more touchsensitive. Too much gain and the preamplifier will clip and
distort. Eventually, high gain settings will also serve to boost
unwanted guitar-pickup noise.
A low impedance, or buffered-bypass, mode can be selected by
moving all four jumpers to the upper-position. In this mode,
the pedal will ensure that signal integrety is preserved even
when driving long cable runs.
"True-Bypass" can be obtained with all four jumpers in the
lower-position.
Jumpers can be simply pulled away and pushed back into
place. Spare jumpers can be easily obtained if required.
Compression is greatly reduced at lower gain settings as much
of the signal entering the compressor section falls below the
compressor's internal threshold. Signal level must exceed this
threshold in order to initiate gain-reduction. In this scenario
only the signal-peaks are compressed.
The "INPUT/COMP" control also varies the amount of signal
routed from the output of first compressor to the input of the
second (refer to the block diagram). This greatly affects
compression levels in the second compressor stage.
Ratio
The Ratio control allows the user to adjust the amount of gain
reduction applied for any given increase in guitar signal. At
the lowest ratio-setting, doubling the input signal (an increase
of 100%) will result in the output increasing by 19%. At the
highest ratio-setting, the output would rise by only 0.2%, for
the same increase in input signal. The latter case represents
extreme "Limiting".
Figure 3: J4, J5, J6, J7: Bypass Jumper-Connectors.
The SlideRig offers the user insane amounts of Ratio, and
higher levels WILL generate distortion artifacts, particularly
when processing chords. If this is a problem, just select a
lower-Ratio setting.
Output
The Output control simply varies the level of signal present at
the pedal's output jack. This can be set in order to keep the
overall effected-level close to the, dry (bypass) signal.
Alternatively, the level can be increased to help project a
guitar solo.
Figure 4: Changing the jumper position on J4.
Rhythm/Solo Presets
Pressing the "SOLO" switch toggles the unit between
"RHYTHM" & "SOLO" modes.
In "RHYTHM" mode, the three dials on the RHS of the pedal
will be active and will offer full control over user-parameters.
In "SOLO" mode the RHS dials become inactive and the dials
on the LHS become active in their place.
Attack & Release (Internal Selection)
Figure 2: Useful Settings: (a) low compression; (b) medium
compression; (c) high compression.
Attack & Release controls are all too often misunderstood,
which is unfortunate as they are instrumental in achieving a
usable sound. In most cases Attack & Release parameters
should be adjusted to optimise the compressor's dynamic
response to that of a particular instrument. However, they can
also be adjusted to create strong dynamic effects.
The SlideRig gives the user some scope to adjust Attack &
Release through the use of internal jumper-connectors. It has
been assumed that once a preferred setting is found that the
user will rarely need to adjust these parameters.
The Attack control determines the time taken for the
compressor to react to the presence of a signal, i.e. the delay
from the instant when you play the note, to the moment the
compressor actually reduces the gain. The longer the Attacktime/delay, the more pronounced the beginning of each note
will sound.
In the context of the guitar - you may make the following
observations when adjusting Attack settings:
Increasing Attack-time highlights the percussive "snap" of
strongly picked notes.
Reducing Attack-time may impart a "spongy" feel to the
character of the compressor - especially when "digging-in" to
single notes!
Reducing the Attack-time to a very short time will result in
undesirable distortion being generated - this will be heard to a
greater extent when playing bass notes.
The Release control determines the duration of any gain
reduction. This would be measured from the time that
compression is triggered to the point that the compressor has
returned to its idle state. For maximum effect when processing
guitar, the Release must be set so that the compressor
responds fully to every note played. If so, the release time
must be short enough for the compressor to fully recover in the
short time between one note ending and the next note
beginning.
Figure 5 shows the "Attack / Release" jumpers in their default
positions. There are two sets of Attack & Release jumpers one for each of the chained compressors (refer to the block
diagram). Settings are applied to both user-presets.
Treble-Lift Selection
When processing a signal with large amounts of compression,
there is a tendancy for treble frequencies to be slightly "rolledoff". This results in a smoother tone, which some may like and
others may dislike.
The SlideRig features an internally-selectible "Treble-Lift"
function. This reduces the amount of compression applied at
treble frequencies, and results in a fuller treble response.
For the truest "Little Feat" tone leave the "Treble Lift" jumper
in the "off" position.
Battery & External Power
The internal 9V battery will provide good-quality operation for
approximately 50 hours. After this time the user may choose
to fit a fresh battery. This can be done easily by removing the
four screws from the base of the enclosure. From here the new
battery just clips into place. Be careful not to knock any of the
components on the circuit-board.
Alternatively, an external supply can be used. A high quality
regulated supply should be chosen to avoid damage from
voltage-surges and other over-voltage conditions. The
connector should be the 2.1mm type with the centre-pin
"Wired-Negative".
For best performance, the pedal should be powered from an
18V supply. This will increase the headroom, allowing cleaner
Figure 5: Attack & Release settings. Comp 1. Attack: Slow /
Comp 1. Release: Medium / Comp 2. Attack: Slow / Comp 2.
Release - Fast.
Figure 6: Treble-Lift jumper. Featuring three positions: "Off";
"Part" (partly-enabled); "Full" (fully-enabled).
processing of conventional guitar signals. This will also permit
the use of hotter source signals, such as active guitar pickups.
It's unnecessary to remove the battery when using an external
supply. There is no risk of damage to either the battery,
supply or pedal. However, as is the case with all battery
powered goods, old batteries are prone to leaking and so
should not be left installed for prolonged periods of time.
About the Designer
"Origin" products are currently being developed by Simon
Keats, of UK-company, Keats Audio. Simon has worked for a
number of big-name "audio" companies, on a full-time basis
and as a design consultant.
Simon can be reached by email, telephone or by post, and will
be happy to help with any enquiries.
Email:
simon@origineffects.com
Telephone:
0800 810 1070
International: +44 800 810 1070
Address:
Simon Keats
Origin Effects
First Floor Office
Unit C6 Station Yard
Thame
Oxfordshire
OX9 3UH, UK
Simon Keats/Origin Effects is not affiliated with Urei or Universal
Audio in any way. This product draws inspiration from the Urei "1176"
compressor, but does not feature any "like-for-like" circuitry!!!
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