Hello.
For Ken's rev 2 circuit, change the 10uF cap before the TL071 to 100 nF.
This is part of a high-pass RC "filter" with a cutoff of 1/(2piRC)
= .15Hz! No need to pass such low frequencies! At 100 nF, we get 15Hz,
which is just sub-sonic, but won't pass the really low DC component. This
helped fix the problem a lot.
-gerald
By the way - thanks Ken for the suggestion on increasing resonance with the
2k2 resistor to ground under the 2n2222 transistor. Worked wonderfully, and
my Steiner filter sounds BEAUTIFUL!
For Ken's rev 2 circuit, change the 10uF cap before the TL071 to 100 nF.
This is part of a high-pass RC "filter" with a cutoff of 1/(2piRC)
= .15Hz! No need to pass such low frequencies! At 100 nF, we get 15Hz,
which is just sub-sonic, but won't pass the really low DC component. This
helped fix the problem a lot.
-gerald
By the way - thanks Ken for the suggestion on increasing resonance with the
2k2 resistor to ground under the 2n2222 transistor. Worked wonderfully, and
my Steiner filter sounds BEAUTIFUL!
On 12/21/06, The Alison Project <alison@...> wrote:
>
> Check back post from about a month ago, seems everyone has this problem.
> Not due to bad pots but DC getting into the pot. I've tried a couple of
> fixes posted on the board and nothing has worked.
>
> ----- Original Message -----
> From: peng3002
> To: cgs_synth@yahoogroups.com <cgs_synth%40yahoogroups.com>
> Sent: Thursday, December 21, 2006 4:51 PM
> Subject: [cgs_synth] Scratchy Synthacon Res pot question and poll
>
> I posted this to the SDIY list. Shoulda tried here first:
>
> I have two Synthacon VCFs built on CGS boards. The third one is on the
> way but before that I need to solve I problem I'm having. Turning the
> Resonance pot produces a scratchy noise. I think this is a common
> problem others have had, too. I'm under the impression that this is DC
> through the pot. I've tried wiring a cap in a variety of ways with no
> luck.
>
> Has anyone built this VCF and DO NOT get scratchiness when turning the
> res pot? To test, turn the inputs down (off) , turn the gain all the
> way up, and turn the res pot back and forth a bunch of times.
>
> I have tried swapping pots (all Alphas, though).
>
> I have two completed modules and one on the board so any suggestions
> or ideas will be carried out immediately.
>
> Thanks in advance,
> peng
>
> [Non-text portions of this message have been removed]
>
>
>
[Non-text portions of this message have been removed]