[sdiy] Matched transistors and EFM circuits?

[David Wagenbach]

I built a YuSynth Arp filter last weekend and as an
experiment I used some 3904 transistors I had not yet
matched. The cutoff kinda works but there are very
uneven steps and a constant ringing. The Resonance is
sort of an overdrive now. It's almost unusable as a
filter, but as an unpredictable distortion and
overdrive module it rocks, sorta. I'll be doing some
transistor matching this weekend.
I have a PCB layout of the Moog matching circuit if
anyone would like it. 
David


--- Harry Bissell & Nora <harrybissell at copper.net>
wrote:

> 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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