[sdiy] dare I say - decoupling?

[Michael Ruberto]

For my new synth I want to use a clean ground + dirty ground setup. What are 
some guidelines as to which devices use which ground? Especially in a 
discreet VCO...

Also, since I am planning to have no less than 5 VCOs what should I do to 
prevent soft-syncing (ground coupling?).
Maybe it would be helpful to me and others if an overall system grounding 
strategy was outlined.

I noticed some people use resistors on the power rail inputs for each 
module. What exactly is gained from this?
would it be a good idea to apply it to all modulation sources?

Thanks, keep the info rolling, I'm learning alot already!!

M. A. Ruberto



>From: James Patchell <patchell at cox.net>
>To: "Michael Ruberto" <frankentron at hotmail.com>, 
><synth-diy at dropmix.xs4all.nl>
>Subject: Re: [sdiy] dare I say - decoupling?
>Date: Sat, 03 Sep 2005 09:46:49 -0700
>
>And just to reinforce what Paul says...
>
>If a rail to rail bypass seems to work better than rail to ground...you 
>better look at your grounds!
>
>I did a linear power amplifier a few years ago that had a persistent 
>oscillation.  Replacing the bypass cap from rail to ground with a rail to 
>rail got rid of the problem...sort of.  Despite the ground traces being 0.2 
>inches wide in 2 oz copper...they were inadequate for the job...the rail to 
>ground just made matters actually worse...but what this was telling me was 
>"Hey, you dummy...you need to add another layer that is a ground 
>plane!"...which I did, finally (I didn't want to...this increased the 
>cost)...but the ground plane solved the oscillation problem and the rail to 
>ground bypasses worked like they were supposed to.
>
>Harry likes to use the analogy of "Ground == Ocean"....very important 
>here...In general, you do not need a ground plane.  But when things don't 
>seem to be working they way they should...well...
>
>By the way, that power amplifier was for a servo system and would put out 
>about +/- 45 volts at 27 amps with a bandwidth of about 20KHz...I might 
>have been expecting just a bit too much from .2 inch wide ground traces 
>(they were not expected to carry 27 amps, but they were the return for the 
>bypass caps on the rails which did carry that current....).
>
>-Jim
>
>At 10:46 AM 9/3/2005 -0500, Paul Schreiber wrote:
>>Rail-to-ground.
>>Rail-to-rail doesn't do *anything* worthwhile. In fact, it can actually 
>>add
>>noise :)
>>
>>Paul S.
>>
>>
>>----- Original Message ----- From: "Michael Ruberto" 
>><frankentron at hotmail.com>
>>To: <synth-diy at dropmix.xs4all.nl>
>>Sent: Saturday, September 03, 2005 10:28 AM
>>Subject: [sdiy] dare I say - decoupling?
>>
>>
>>>Well we know who the decoupling experts are here, and they do shine so 
>>>brightly. At the risk of sounding like the moron I am I must pose 2 
>>>questions to the decoupling kings.
>>>which is better, decoupling caps from each rail to ground, from rail to 
>>>rail, or both?
>>>what's the difference?
>>>what is the air-speed velocity of an unladen swallow?
>>>thanks in advance oh wise ones ;-)
>>>M. A. Ruberto
>
>         -Jim
>***************************************************************
>http://www.oldcrows.net/~patchell
>
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>