User`s manual

 The original gain potentiometer is used in “rheostat” (2-pin) configuration; this is the case with standard 3-pin

potentiometers if the wiper is connected to one of the other terminals.

 The original gain potentiometer has a nominal value between 5k or 50k. Larger values are possible, but

require other type of optocouplers. Please contact us with your requirements.

 The minimum resistance with the supplied NSL-32SR2 couplers is about 40 Ohms. Depending on your

preamp model, this may limit the range of gain adjustment which can be achieved (in case of ADA8000, the

gain range which can be remoted is from +10dB to +50dB; vs. the original range of +10dB to +60dB. This is

rarely a problem as most preamps produce a significant amount of noise in the high gain ranges).

 Some preamps use stereo (or even more channel) potentiometers for gain control. It is possible to mod such

models by adding additional optocouplers in series configuration, but you may need to swap the voltage

regulator inside the RGC-24A-M to compensate the higher forward voltage of the coupler's LEDs. Please

15.4. Matching the control curve to your preamp

The remote gain controller is a precision, low-noise current source which controls the optocouplers light sources

(LEDs). It delivers a controlled current in the range of 0 … 25mA, adjustable in 10bit precision (1024 linear steps,

or about 24µA/step). Because gain control is usually done using a log taper potentiometer, and also the

optocoupler has a log control characteristic, one must emulate logarithmic behavior of “gain” vs. “output current”

by software. This results in control curves are usually flat at the lower gain ranges (only a few bits per step), but

very steep at the higher gains.

15.5. Reset to Factory Defaults

CAUTION: Resetting to Factory Defaults causes loss of all user-defined curves and parameters which were

altered using SYSEX commands!

To restore the factory defaults, perform the following steps:

 Remove power from the RGC

 Hold down “ACTIVE” button while re-connecting power

 Continue to hold down the button until the yellow “ACTIVE” LED flashes three times

The factory defaults are now restored.