[sdiy] Which transistors for synth circuits?

Gordonjcp gordonjcp at gjcp.net
Thu Dec 30 21:30:51 CET 2021

On Thu, Dec 30, 2021 at 07:18:32PM +0100, cheater cheater via Synth-diy wrote:
> Hi all,
> I was wondering how you pick out transistors (as well as diodes) for
> synth circuits like filters. For example moog filter, 303 filter, etc.
> Do you look for anything in specific? I'm talking about a situation
> where you don't want to use the exact part in the schematic, but want
> to play around with parts and see what comes out of it.

Any two transistors you pull out of a bag of a thousand from some dude in China totally at random will be more closely matched than the "super matched pairs" we spent so much money on in the 80s.

The big difficulty these days is that random pick'n'mix from some Chinese dude on eBay is going to be so much higher quality than the parts used in vintage synths that they won't be "wrong" enough to work for some applications.  While a reversed transistor makes a good noise source even now, you may have to try a few to get enough noise out of it!

With a very few exceptions none of the components used in vintage synth circuits are especially finicky and almost any transistor will work.  I tend to keep a very large stock of BC548/BC558, 1N4148, and TL07x, and of course LM13700s.  With that I reckon I could build pretty much any part of an analogue synth voice, to any one of a few dozen designs.  If you want to get crazy with it, throw in some LM3900s (ARP "patent buster" filter, among others) and CD4069UBE (EDP Wasp/Gnat SVF and absolutely *gorgeous* "valve sound" distortion).


More information about the Synth-diy mailing list