[sdiy] keeping signals seperate..avoiding noise

nicolas nicolas3141 at yahoo.com.au
Fri Nov 14 12:12:06 CET 2008


Actually if the coupling is capacitative then you want to reduce the voltage (especially the high frequency AC) of the nasty circuit rather than the current.  Either way the aim is to change the balance of power by reducing the offending current and voltage and boosting the current and voltage in the circuit you want to sound cleaner.

Cheers,
Nicolas


--- On Fri, 14/11/08, nicolas <nicolas3141 at yahoo.com.au> wrote:

> From: nicolas <nicolas3141 at yahoo.com.au>
> Subject: Re: [sdiy] keeping signals seperate..avoiding noise
> To: synth-diy at dropmix.xs4all.nl
> Received: Friday, 14 November, 2008, 11:28 PM
> 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
> > 
> > 
> > --------------------------------------------
> > check out various dan music at:
> > 
> > http://www.myspace.com/lossnyc  
> > 
> > 
> > http://www.soundclick.com/lossnyc.htm
> > 
> > 
> > http://www.indie911.com/dan-snazelle
> > (or for techno) http://www.myspace.com/snazelle 
> > 
> > 
> > 
> > _______________________________________________
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> 
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