[sdiy] Matched transistors and EFM circuits?

[Harry Bissell & Nora]

In my experience with the EFM boards (in particular the ladder
circuit) unmatched transistors result in severe DC offsets as you sweep
the filter center frequency.  So bad in my case thatI had to add
a shunt regulator to the bias capacitor (in a Moog its about 220uF
and the EFM should be that big as well...).

Using matched transistor pairs eliminated that problem totally.

Matched transistors were better sounding (onset of resonance was
smooth and repeatable)

In the MS-20 clone, the matched transistors might make the current
sources a little better with temperature. If you are not using
tempcos, why bother ???

H^) harry

Harry Bissell loves Nora Abdullah
Married Nov 6th 2006

--- djhohum at gmail.com wrote:

From: "dj hohum" <djhohum at gmail.com>
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Matched transistors and EFM circuits?
Date: Thu, 7 Jun 2007 16:56:15 -0700

I just received a couple of PC boards today from EFM, I like them a
lot. Small, clean, well made, fast service.

Anyway, it's well known, or at least often discussed, that one should
match the transistor pairs in a ladder filter. This also holds for
exponential converters. Should I also do this for the various pairs in
the 3526 (korg MS-20 clone)?

In any case, how do the properties of unmatched transistors manifest
themselves in the resulting sound?

Thanks,
Daryl
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