CGS Serge voltage controlled gain cell (view source)
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[[File:cgs_cgs108_vca.jpg|thumb|center|850px|]]
'''CGS108''' the '''CGS Serge voltage controlled gain cell''' is a sub-module used in many of Serge's designs, such as the various voltage controlled filters, Quad VCA, mixers, panners and so on. The circuit is proprietary, and I do not have permission to share the schematic. It is sufficient to say that it is essentially a [[voltage controlled op-amp]]. It can be used in amplifiers and integrators.
This sub-module will work on +/-12 or +/-15 volts.
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Note that the orientation for the transistors on the overlay is for BC547B and BC557B transistors. The pinout of modern PNXXXX devices is usually the reverse of what was used with the 2NXXXX devices. PN4250 (use instead of BC557B) would need to be installed backwards with respect to the "D" on the overlay. 2N5089 (use instead of BC547B) has variant pinouts depending on manufacturer. Check with the datasheet for the brand you have purchased.
Like types of transistors must be matched, more so with the NPN pair, as the trimpot can deal with some degree of mismatch in the PNP pair. See one of the other online resources for transistor matching, or follow the [[CGS
[[File:cgs_photo_cgs108v10_vca.jpg|thumb|center|150px|]]
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.
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[[File:cgs_photo_cgs108_header.jpg|thumb|center|545px|Header fitting example. Once soldered, the plastic carrier is carefully clipped away with a pair of side cutters, leaving long pins. The long pins will be trimmed when fitting the module to the carrier PCB.]]
{| class="wikitable"
|+ style="text-align:left"|Pad identification
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! Pad ID!!style="text-align:left"|Function
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== Setup ==
[[File:cgs_schem_cgs108_setup.gif|thumb|center|369px]]
To correctly adjust the CGS108, it needs to be wired into the circuit shown above. It can
A scope is connected to the output. The scope is set to DC, and the beam centered on the screen. Vertical amplification can be set at 2V or 5V per division, and can be adjusted as needed to keep the trace on the screen.
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* 330R refers to 330 Ohms. 100 nF = 0.1 uF, etc.
* PCB is 1.4" x 1".
== 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.
== See also ==
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== References ==
* [https://web.archive.org/web/
== External links ==
* [http://bompiler.com/pcb/cgs108 CGS108 BOM] at BOMpiler
* [http://groups.yahoo.com/group/cgs_synth CGS Synth discussion group], for discussion of locating parts, modifications and corrections etc.
* [http://www.deliandiver.com/serge-gain-cell Serge Gain Cell], schematic at the Delian Diver website
* [https://www.modwiggler.com/forum/viewtopic.php?p=3503106 Serge/cgs108 gain cell vca], Mod Wiggler Forum, Apr. 2021
* [https://patents.google.com/patent/US3518578A/ US patent 3,518,578], ''Signal compression and expansion system'' by Thomas Stockham and Alan Oppenheim, 1967 - a diode precursor of the Serge gain cell <!-- <ref name="cgs108">[https://www.modwiggler.com/forum/viewtopic.php?p=3503106 Serge/cgs108 gain cell vca], Mod Wiggler Forum, Apr. 2021</ref> -->
* [https://patents.google.com/patent/US3714462A/ US patent 3,714,462], ''Multiplier circuits'' by David Blackmer, 1971 - a transistor precursor of the Serge gain cell<!-- <ref name="cgs108"/> -->
[[Category:CGS
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