[sdiy] Digital / Analog Noises

[Bill Berzinskas]

10-4..  i'll try that out today when i get a chance.. what was the 
consensus.. 1uf or .1?

----- Original Message ----- 
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, March 30, 2005 9:58 AM
Subject: Re: [sdiy] Digital / Analog Noises


> "Bill Berzinskas" <wberzinskas at nc.rr.com> wrote:
>>Hello everyone..  as you might know by now i've been heavily modifing
>>the adv-bass circuit..   so currently, ive got it running off of 5v, and
>>got the digital pots all working..   Although, i'm having a few problems
>>with noise..
>>
>>First..   At the final output stage, I am getting noise, although not
>>before it..  This sounds like it could be digital, or it could just be a
>>really low SN ratio..   So it's getting into the summing matrix
>>somehow..   I've changed this to just a regular non-inverting summing
>>amp..   which seems to me to be ok..    Any clues?
>>
>>Also,  I'm using the oscillator design from the LM158 Datasheet (Same
>>setup as the DS-7 Clone)..   And i'm getting a small bit of the square
>>wave into the signa..  whats up with that?!   i'm tinking it has
>>something to do with the virtual ground setup..  but i'm not sure..
>>Anyone?   :-)
>
> I would doubt it unless you're trying to use it in a too high current
> application.  IMHO, it sounds like you didn't adequately or correctly use
> bypass capacitors.  I would have bypass caps from 5volts to Vground and
> from 0volts to Vground.  This mimics how you would bypass a real dual 
> supply.
>
> If you think the Vground is a problem current wise, you can increase it's
> current handling capacity by paralleling two or more opamps.  You can also
> test for and measure this condition by using an oscilloscope to monitor 
> the
> voltage between any rail and Vground.  Ideally, the voltage should not 
> change.
>
>>Also, I can hear clicks when i change a digital pot.. i'm thinking this
>>is simply because it's stepped, but they seem rather loud.. what can i
>>do about that?
>
> Still sounds like bypass to me.
>
>
>>And while we're on this subject..  what precautions should I take in
>>layout, construction to help curb these problems? I'm thinking of
>>construction the Analog and Digital section on seperate boards and
>>interconnecting..  Would def be easier on me as far as working on it..
>>anyway..  any input would be awesome!
>
>
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