Cgs synth

--- In cgs_synth@yahoogroups.com, "peng3002" <peng3002@...> wrote:
>
> 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
>

From: peng3002
To: cgs_synth@yahoogroups.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]

>
> 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
>

>Check back post from about a month ago, seems everyone has this problem.

>
>

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]

>
> 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.

> helped fix the problem a lot.
>
> -gerald
>

--- In cgs_synth@yahoogroups.com, sasami@... wrote:
>
> The solution that supposedly works is to wire the 1k pot outer terminals
> into the circuit instead of an outer and the wiper. One then adds a
> capacitor between the wiper and one end. The result is that the DC
passes
> through the 1k as required, and the wiper only ever sees AC.
>
> The other solution is to just accept it as a feature of the design.
>
> Ken
>
> >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.
> >
> >
> _______________________________________________________________________
> Ken Stone sasami@...
> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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>