[sdiy] Diode-ladder Filter problems

[Dave Leith]

yes I also built this and had some problem with CV input circuit. I
think I ended up putting a small resistor (~ 600 to 900 ohm) in series
just at the bottom of the ladder between the exponential circuit and
the ladder. (At some point I had fried the CV circuit with too much
input voltage - hence the limiting resistor) . Got it working, sounds
OK, resonance not the best sounding, then found the real EMS circuit
somewhere on the web. It works great. But it needs some extra work
with additional buffers. I believe the YUsynth variation represents a
very good working version to consider.
http://yusynth.net/Modular/EN/EMSVCF/index.html

On 7/6/08, Ian Smith <taciturn_unquiet at hotmail.com> wrote:
>
>  Mike,
>
>  Thanks for the tips. I'll go back and rework it when I have some more diodes. I think I have maybe 5 left after this project. Blasted thing works sorta ok when I had my function generator running through it but didn't work at all with my SH-201.
>
>  Ian
>  ________________________________
>  > Date: Sun, 6 Jul 2008 15:45:39 -0400
>  > From: somnium7 at gmail.com
>  > To: taciturn_unquiet at hotmail.com; synth-diy at dropmix.xs4all.nl
>  > Subject: Re: [sdiy] Diode-ladder Filter problems
>  >
>  > Ian,
>  >
>  > I built this many years ago and remember all kinds of problems with the CV input circuit. I wound up replacing it all with the standard PNP/NPN v-i converter. After that the VCF started filtering but then I didn't like the range of the resonance so I think I wound up changing the gain on the feedback opamp.
>  >
>  > Sorry I can't give you specifics this is all from memory and that was the late 90s so things are kinda sketchy.
>  >
>  > I suggest reworking the circuit. I have always felt that particular schematic has a mistake in it.
>  >
>  > Mike
>
> >
>  > On Sun, Jul 6, 2008 at 2:58 PM, Ian Smith  wrote:
>  >
>  > Hey all,
>  >
>  > I just finished building this Diode Ladder Filter, http://www.freeinfosociety.com/electronics/schemview.php?id=329 and it sounds all not filtery and very staticy. Could it be the transistors I used? I put in 2N3904's instead of the BC109C's because it's what I have on hand. I used a TL074 instead of the 3 LM741's, and 100k pots for VR 1 and 3, and a 1M pot for VR 2. Other than that everything is the same.
>  >
>  > Thanks,
>  >
>  > Ian
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