CGS Serge dual channel stereo mixer

CGS101 the CGS Serge dual channel stereo mixer (DCSM) module is a variation of the Serge Dual Channel Stereo Mixer, built using the CGS108 VCA and the CGS102 Equal Power Panner drivers.

The unit will run on either +/-12 volts or +/-15 volts.

Description
The dual channel stereo mixer (DCSM) is an alternative output VCA/mixer/panner for two and three-panel systems. The dual channel stereo mixer is used for the standard output level control (or enveloping) and for voltage controlled panning. The DCSM has two independent channels for stereo panning. Each channel in the DCSM has two VC inputs, one for amplitude control and one for panning. The panning controls are opposite for the two channels, so that if a single control voltage is used, the output signals will pan in opposite directions. Auxiliary inputs are used to feed other signals into the outputs of the module. Signals applied here will not be affected by knobs or control voltages applied to the module. These are mainly useful for linking other mixers (either manual or voltage controlled) to the output bus. The output is available at a pair of banana Jacks (for routing the signals to other modules within the synthesizer), and at mini-Jacks (for connecting to external amplifiers, tape decks, and other equipment).

Construction
The CGS101 DCSM uses four CGS108 Serge gain cells as it's voltage controlled elements. Refer to the CGS108 page for construction details.

It also uses two sets of CGS102 CGS Serge equal power panner boards. Refer to the CGS102 page for construction details. These submodules should be the last things you install on the CGS101 PCB.

Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with low profile components such as resistors and diodes first, followed by successively taller components.

Take particular care with the orientation of the polarized components, such as ICs, electrolytics, diodes, and transistors.

When inserting the ICs in their sockets, if used, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

'''The first time you power it up, I would suggest you do so with 22 ohm resistors in series with the positive and negative power rails. This should save the chips if you have made a blunder.'''

On the CGS101 VER1.0 PCB there are some corrections required. There may be some confusion regarding the panel layout and marking of this module. There are two input channels, and two output channels. The input channels are called Channel 1 (on the left) and Channel 2 (on the right). Above them are the two output channels, each with an auxiliary input and a pair of outputs, with the left channel to the left, and the right channel to the right.
 * Four 5k6 resistors need to be installed on the rear of the PCB. Each resistor goes between pins 7 (CV) and 8 (0V) of one of the CGS108 submodules.
 * Two connections to each CGS102B submodule need to be reversed. Fortunately this can be done entirely on the rear of the PCB by cutting the tracks in the areas shown in light green on the diagram below. After some solder mask is scraped from the remaining track stubs, (shown in copper below) six links can be added. The four links shown in blue can actually be replaced with two short lengths of component wire offcuts. The two links shown in purple are best if done with insulated wire as they pass over other pads.
 * Two wires need to be connected to pads directly below the submodules. See the diagram for details.

Take care not to confuse Channel 1 with the Left output channel, or Channel 2 with the Right output channel.

Setup
There should be no setup required, other than to set the trimmers on the CGS108 PCBs as described on that page.

Parts list
This is a guide only. Parts needed will vary with individual constructor's needs.

CC-BY-NC
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work. Serge Tcherepnin retains all rights to his work.

Suppliers

 * CGS101 Dual Channel Stereo Mixer, revision 1, Elby Designs