Cgs synth

Hi there,

I'm attempting to put together my first project (the steiner vcf) and
am somewhat confused about capacitors and which ones to
use. Beyond the values listed for the circuit I'm wondering if it
makes any difference the type of capacitor used (ceramic,
electrolytic, etc). Also some of the capacitors required are listed
as 25v and 35v in addition to the capacitance values so I'm
wondering if this means the caps have to be those values or
higher or specifically those values. My apologies if these are
dumb questions. Thanks in advance for any advice.

>
> I'm attempting to put together my first project (the steiner vcf) and

A nice and different filter - I use this one as much as any others that I
have.

> am somewhat confused about capacitors and which ones to
> use.

Welcome to the club - these things drive me crazy.

Beyond the values listed for the circuit I'm wondering if it

> makes any difference the type of capacitor used (ceramic,
> electrolytic, etc).

Actually, yes. Electrolytics used in synth modules are bipolar (a + side
and a - side). Ceramics, metal film, ... are not bipolar. There are
others here who are much more qualified than I to expound on capacitors.

Also some of the capacitors required are listed

> as 25v and 35v in addition to the capacitance values so I'm
> wondering if this means the caps have to be those values or
> higher or specifically those values. My apologies if these are
> dumb questions. Thanks in advance for any advice.
>

Not dumb questions at all. The cap's with voltages most likely refer to
the radial electrolytics. These are typically specified with 2 values,
Farads (or nano-..., ...) and voltage. Higher voltages are typically ok
to use, but the higher the voltage, the larger the electrolytic so try to
stay with the recommendation so that the electrolytics are good neighbors
to nearby components.

Some references:
Specifically for the STeiner, Bob Knarley has a parts page at:
http://www.bobknarley.com/synth/cgssynthaconvcf.html

He also has parts for some other CGS modules.

Parts for some modules can also be found on one of Larry Hendry's pages:
http://www.wiseguysynth.com/larry/cgs/cgs.htm

Codes for some capacitors (which I can never figure out) are at:
http://www.bobknarley.com/synth/capcodes.html

HOpefully this will get you started, Jeff

The only critical caps in the Steiner VCF are the caps for the
integrator/filter sections, the 2N2s. For mine I am ordering some
Polystyrene, 2200 pF, radial caps from Mouser, part number 23PW222. These
are high stability, low temperature coefficient, 5% tolerance caps.

You can always use a higher rated capacitor voltage rating than listed.

Most caps in CGS designs are decoupling or simple RC circuits for generating
triggers or delays. For those I generally use the cheapest cap available
with the proper pin spacing. For the standard 100N decoupling cap I've been
using Mouser part number 80-C322C104M5U. These are only 11 cents each in
quantities of 25 or more.

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com

> Actually, yes. Electrolytics used in synth modules are bipolar (a + side
> and a - side). Ceramics, metal film, ... are not bipolar. There are
> others here who are much more qualified than I to expound on capacitors.

It is more accurate to call most common electrolytic caps unipolar -
polarity is important. There is such a thing as a bipolar electrolytic
where polarity doesn't matter and these are used occasionally in synth
circuits.

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com