[sdiy] Matching transistors in "diode ladder" filters

[JH.]

The EMS VCF has a DC negative feedback path (independent of the resonance 
setting!), which helps to "center" your bias point even without tightly 
matched components. I haven't tried it, but I wouldn't be surprsed if it'd 
also work with completely unmatched parts.

JH.


----- Original Message ----- 
From: "yves usson" <yves.usson at imag.fr>
To: "Aaron Lanterman" <lanterma at ece.gatech.edu>; "synth- >> synth diy" 
<synth-diy at dropmix.xs4all.nl>
Sent: Sunday, April 20, 2008 9:38 AM
Subject: Re: [sdiy] Matching transistors in "diode ladder" filters


Hi Aaron

In my recreation of the EMS diode ladder filter I used simple 1N4148 and
I selected
within the same batch those which forward drop voltages were similar
within a range
of 3mV. If you take diodes from the same batch you will see that the
tolerance is quite
good indeed and in order to have 7 matched pair you need not to test
more than 20 diodes.

http://yusynth.net/Modular/EN/EMSVCF

Cheers

Yves Ussson
http://yusynth.net



Aaron Lanterman a écrit :
> One of my students is working on building a variant of the Roland 100 VCF:
>
> http://fa.utfs.org/diy/roland100/101_op27.jpg
>
> See lower half, 3rd "block" from the left.
>
> I've heard that in the Moog ladder, it's important to match the top
> transistors and the bottom transistors, but the ones in the middle
> aren't so important to match (and some schematics of various Moogs bears
> this out.)
>
> Does anyone have advice of what is important to match in a "diode
> ladder" filter? We're doing the Roland 100, but I the same question
> could apply to TB-303, EMS, and Sonic V (IIRC).
>
> I told my student to use CA3046s to get some cheap pairs (since I have a
> bunch), but if he could use garden variety diodes for some that would be
> convenient.
>
> - Aaron
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> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>

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