Empirical Labs EL-Rx - Manual (Page 4)

and turns the input into a balanced amplifier, allowing the DocDerr to handle very hot signals without
clipping, and the module becomes a great mix or line level tracking processor.
3 Pin Jumper Settings
Above is a diagram pointing out the 3 user selectable jumpers, affecting audio and compressor
detector. All jumpers are shipped in the left (front) position, which is factory default.
INPUT GAIN JUMPER - For direct instrument inputs, such as an acoustic guitar, one would set the
INPUT GAIN Jumper to the right (NOT as shown). This provides 16 dB of single ended gain when
input pin 3 is shorted to ground, as a normal guitar cable would do. This gain is usually enough to
bring up electric instruments to line level, while still providing a margin of safety for certain active
instruments. It will help the MIX control also, making the dry level closer to the compressed level, so
sweeping between them won’t be so radical. For line level signals, keep jumper to the left (front).
DETECTOR HP JUMPER - This jumper allows the user to optionally roll off low frequencies going to
the detector of the compressor. When in the right (rear) position, this filtering keeps the compressor
from responding as much to the low frequencies, which often have great power, therefore sometimes
getting over-compressed, subjectively speaking. However, since the compressor is so versatile, it’s
usually preferable to tame the subs as well, by sending a full bandwidth (FBW) signal to the
compressors detector (jumper to the left as shown).
DIFFERENTIAL OUT JUMPER – Changes output configuration. This jumper sets the XLR output
pin 3 to either balanced ground, or the inverted phase of what’s on pin 2 of the output XLR. It is set
to the left, differential mode, from the factory, adding 6 dB more gain. Setting the jumper to the right
(towards the rear) disconnects the amplifier on pin 3, decreasing the output gain by 6dB.
Multi-Button Controls: Lastly, to get started you should learn three special button combinations.
Pressing two buttons at once will cycle through the following parameters:
HP Frequency - Press LF and MF to change HP Frequency from Off, 70Hz, and 100Hz.
Mid PEQ BW - Press MF and HF to change Mid band Q (bandwidth). LED indicates narrow Q.
Disable Compressor - Press LF and HF to disable/enable compressor.
3
Disabling the compression can be done with software by pushing the LF and HF buttons
simultaneously, allowing the DocDerr to behave almost as a tape-like saturation/distortion box.
A Det HP jumper on the PCB can make the compressor respond less to low sub frequencies.
The DocDerr is shipped in FBW (full bandwidth) mode, with the jumper towards the front, which is
usually preferable, especially bass instruments. Moving the DET HP jumper to the rear position rolls
off below 150Hz to the compressor detector, and can help prevent LF pumping for midrange sources
like vocals and acoustic instruments. It is sometimes useful for buss compression as well. The HP
EQ filter often prevents pumping also, as it filters out subs in the audio path before the compressor
sees them. See P3.
The Saturator
The saturation circuit follows the compressor, and tends to catch high frequency peaks that get
through, softly flattening them out. It was largely tailored to simulate the characteristics of tape
saturation. Germanium semiconductors are used to more smoothly round the peaks to produce
lower order harmonics. We use special filter circuits to shape how different frequencies are soft
clipped. This saturator circuit is always in the path of the compressor signal. When the mix control
is set to 0 (dry), the saturator and compressor are both out of the path and do not affect the output
signal. The saturator will add lots of harmonics to low frequencies, and soften high frequencies.
As mentioned above, pressing the LF and HF buttons will toggle the compressor off and on,
allowing you to use just the germanium saturation circuit with no compression. Very tape-like!
The Mix Control
This is a clean mixing circuit that allows the user to blend the EQ’d uncompressed signal with the
EQ’d, compressed and saturated signal, and has incredible phase alignment through 20KHz. This
simple circuit gives the user incredible flexibility in how the compressor/saturator is used. As already
mentioned, the user can sometimes put lots of compression on a signal, and mix it back under the
dry signal and get a natural full sound, with dynamics, and lots of sustain. There will be a slight level
drop in the middle of the Mix knob range, partially because the compressed signal sustains notes
tremendously, but the uncompressed peaks are attenuated. Once you back down from 10 on the
Mix, the loud sustained level will drop quickly, but you may have a very nice natural dynamic sound.
Conversely, you will also notice a quick change in the loudness and sustain, when you nudge the
mix control above 0. The mix control is heavily dependant on the input signal’s level. There are lots
of marks on the Mix control to aid in recalling settings, especially between 8 - 10.
Wiring the DocDerr
There are two main ways to setup and wire the input of a rack with the DocDerr module installed.
1) “Instrument In” with a single ended input (usually a mono standard guitar cable) and 16dB of
gain,
2) “Line In” which is lower gain and can be differential.
There is an INPUT GAIN jumper located in the middle rear of the board that can be switched
between two positions, Instrument In (Inst) and Line In. This jumper changes the mode which the
input amplifier works, changing it from a high impedance amplifier with gain, to a lower impedance
differential input amplifier with no gain. So before installing your module, set this jumper to the
proper position.
Most API 500 compatible racks do NOT have a 1/4” guitar jack input, so we supply a female
1/4” jack adapter that goes to male XLR. Plugging a standard guitar cable into this adapter will work
perfectly for “Instrument In” mode. The guitar cable will short the sleeve to ring, shorting the ring (pin
3 on the XLR) to ground. When the Input Gain jumper is set to the rear in “INSTRUMENT IN” mode,
this will result in a very clean 16dB of high impedance gain.
As shipped from factory, the output is balanced differential, and 6dB louder than the alternate
single ended output setting. The single ended mode, with the jumper to the rear, has balanced
impedance, which can prevent any output wiring problems (See P3). For recording you will usually
use the balanced differential mode as it has 6dB more gain and will hit the recorder with a better
signal. If too loud, use single ended mode. When using the differential out mode, don’t short any of
the Active XLR output pins (usually Pin 3) to ground. Let the unused pin 3 “float” (stay
unconnected). Separate amplifier drives each of these pins, so grounding one of them will short the
associated amplifier out. So in the Dif Out mode, if you only use pin 2 on your output cable, leave
pin 3 unconnected. When going to a single ended patch bay or other device, using the single ended
jumper setting (jumper towards rear) will work just fine, and take some guesswork out of wiring.
12
Det HP Differential Out
DI
PreOut
16dB
FBW
Dif
50V
U1
U3 4
U9 8 U7 5
11 U12 13 U14
29
27 28
U19 18 U17 16
25
U2
S
/N
________
DocDerr R3
Empirical Labs
5/20 2011 c
Input Gain
Line Inst +16 FBW 150Hz HP Dif out Single Ended
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