[sdiy] keeping signals seperate..avoiding noise

nicolas nicolas3141 at yahoo.com.au
Sat Nov 15 09:52:06 CET 2008


Hi Dan

This op-amp arrangement looks fine as long as all the resistors and cap are physically close to the chip, with the wire run attached where it says INPUT.  From pin 1, where you take the signal off in 2 different directions is that via resistors, etc?  I think the connection to the divider chip should be something like TL074 pin 1 to a diode, then from the diode to two 100K resistors, the other end of one of the resistors connected to ground and the other end of the other 100K resistor connected to the divider chip input.

But power supply or ground issues sounds like it could be the problem as per the other suggestions.

Cheers,
Nicolas


--- On Sat, 15/11/08, Dan Snazelle <subjectivity at hotmail.com> wrote:

> From: Dan Snazelle <subjectivity at hotmail.com>
> Subject: RE: [sdiy] keeping signals seperate..avoiding noise
> To: nicolas3141 at yahoo.com.au, "sdiy" <synth-diy at dropmix.xs4all.nl>
> Received: Saturday, 15 November, 2008, 1:08 AM
> I dont really understand what you mean about lowering the
> input impedance. could you explain a bit how impedance might
> help?
> 
> take a look at the first opamp in this schematic:
>  
> http://www.musicfromouterspace.com/analogsynth/GUITARSYNTHAUG2007/subcommanderschempg1.gif
> 
> i used ray's (first only) opamp as a model of how to
> create a non inverting input
> 
> at pin 1 I make the split (which currently is just one wire
> going to the PLL circuit and one wire going to the x10 amp)
> 
> maybe i should lower the voltage of the PLL? 
> 
> would putting just the dividers on their own regulator
> (with a lower voltage) help?
> 
> thanks for all the tips guys!
> 
> 
> 
> --------------------------------------------
> 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 
> 
> 
> 
> 
> > Date: Fri, 14 Nov 2008 03:12:06 -0800
> > From: nicolas3141 at yahoo.com.au
> > Subject: Re: [sdiy] keeping signals seperate..avoiding
> noise
> > To: synth-diy at dropmix.xs4all.nl
> > 
> > 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  wrote:
> > 
> >> From: nicolas 
> >> 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
> >>  wrote:
> >> 
> >>> From: Dan Snazelle 
> >>> 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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