[sdiy] keeping signals seperate..avoiding noise

[nicolas]

Signals and noise can jump from one wire to the next if bundled.  Obviously you can look at separating your wires or shielding them, etc.  

Also look at whether the interference is coming through ground.  You may need separate grounds for the digital and analogue signals.

The other thing to look at is currents.  If nasty signal A is bleeding into nice signal B then increasing the currents in circuit B and decreasing them in circuit A will improve the situation.  The audio engineer's way to think of this is that you should lower the impedance in the nice signal's circuit and raise the impedance for the nasty stuff.

In this case it sounds like in the pre-buffer stage you may be running at too high an impedance.  Unless there are other strong reasons for that, try reducing the impedance with a resistor to ground (maybe in the 10-100K range) immediately adjacent to the buffer input.  Just make sure that wherever that signal is coming from it is happy to drive into that lowered impedance.

Cheers,
Nicolas


--- On Fri, 14/11/08, Dan Snazelle <subjectivity at hotmail.com> wrote:

> From: Dan Snazelle <subjectivity at hotmail.com>
> Subject: [sdiy] keeping signals seperate..avoiding noise
> To: synth-diy at dropmix.xs4all.nl
> Received: Friday, 14 November, 2008, 5:29 PM
> a few questions
> 
> if i have a clean source going through a buffer and then
> that splits into one half going into a PLL and a divider and
> the other half getting boosted by a x10
> opamp stage...WHY would i be hearing the divider sounds in
> the background of the clean stage?
> 
> this is very different than my lfo bleedthrough of the
> other night (into the vco) but it is similarly noisy.
> 
> i have all pcbs on metal standoffs going into a metal
> box....could this cause the high frequencys of the PLL
> signal (and octave down) to bleed into the clean opamp?
> (though none of the standoffs touch traces)
> 
> maybe i should put a regulator JUST on the divider board?
> 
> i have bypass caps.
> pretty good ground planes.
> and seperate lines for digital and clean grnd.
> 
> what about a bunch of wires laying all over each other or
> being bundled...can this cause signals to mix?
> 
> i think i really need to understand noise better.
> 
> any good books on this?
> 
> thanks
> 
> 
> --------------------------------------------
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> 
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> 
> 
> http://www.soundclick.com/lossnyc.htm
> 
> 
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> 
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