[sdiy] keeping signals seperate..avoiding noise

nicolas nicolas3141 at yahoo.com.au
Sun Nov 16 04:19:26 CET 2008


Hi Dan

Then I am guessing that the divider is a CMOS 4xxx chip getting powered from V+ and ground.  With your op-amps powered from V+ and V- and ground in those circuits just being used as a signal reference voltage.

So inside the CMOS chip there are protection diodes that kick in whenever you try to take an input outside its supply voltages.  In this case the signal from the op-amp is taking things below ground.  Whenever this happens it is either stuffing up your main signal or it is reflecting crap onto the ground.  Or a bit of both.  Kind of like a fuzz pedal applied to only the -ve half of the signal.

So adding the diode you added means the CMOS only sees the +ve half of the signal.  And you don't get the crap reflected back into the rest of the circuit.  The 100K to ground at the CMOS input is necessary so that it sees a grounded input during the -ve half of the signal when your added diode is blocking.

Horowitz and Hill - The Art of Electronics - taught me the very helpful technique of anthropomorphising the various chunks in my circuits and then trying to see the rest of the circuit (currents, voltages, etc) from the point of view of particular components.  If you can get yourself a copy, by the time you have read and understood even just the first few chapters, you will find this kind of problem much easier to tackle.

Cheers,
Nicolas


--- On Sun, 16/11/08, 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
> Received: Sunday, 16 November, 2008, 5:37 AM
> could you explain the diode/100k thing a bit?
> 
> i tried it. here are my results
> 
> i had to just go 100k to grnd but no resistor (as of yet )
> going to divider as 100k must have been too high and messed
> with the tracking. ALSO i find that with the diode, the
> sensitivity knob (gain) has to be turned up. (voltage drop
> must do this??)
> 
> anyway...this diode thing is the ticket! without sounding
> too confident...it wiped away the bleed through.
> 
> but i was wondering...should i be putting a resistor
> between every input/output point? in other words, there are
> a total of 5 seperate boards.   the clean guitar goes into a
> ring mod, the dirty and divider and clean all go into an
> ssm2044 filter,etc. i am wondering if when i go into the
> ring mod on the asm2 if i will need any additional
> resistors.
> 
> let me explain why i am wondering.
> 
> impedance theory is still very very elusive to me.
> 
> I had thought resistors were really only necessary as far 
> as the start and end of circuits were concerned when going
> into JACKS so that the impedances would match between 2
> circuits. but i (must wrongly) thought it did not matter as
> much when dealing with buffered internal circuits and in
> most cases if needed, i would use a 1k. obviously things
> were working on the divder cicuit without a resistor going
> in but THE NOISE WAS FAR WORSE!!
> 
> i would love to find a book that covers this stuff in
> detail!
> --------------------------------------------
> 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: Sat, 15 Nov 2008 00:52:06 -0800
> > From: nicolas3141 at yahoo.com.au
> > Subject: RE: [sdiy] keeping signals seperate..avoiding
> noise
> > To: synth-diy at dropmix.xs4all.nl
> > 
> > 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 
> > > >>> 
> > > >>> 
> > > >>> 
> > > >>>
> > > _______________________________________________
> > > >>> Synth-diy mailing list
> > > >>> Synth-diy at dropmix.xs4all.nl
> > > >>>
> > >
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> > > >> 
> > > >> 
> > > >>       Make the switch to the world's
> best
> > > email.
> > > >> Get Yahoo!7 Mail!
> http://au.yahoo.com/y7mail
> > > >> 
> > > >>
> _______________________________________________
> > > >> Synth-diy mailing list
> > > >> Synth-diy at dropmix.xs4all.nl
> > > >>
> > >
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> > > > 
> > > > 
> > > >       Make the switch to the world's
> best email.
> > > Get Yahoo!7 Mail! http://au.yahoo.com/y7mail
> > > > 
> > > >
> _______________________________________________
> > > > Synth-diy mailing list
> > > > Synth-diy at dropmix.xs4all.nl
> > > >
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> > 
> > 
> >       Make the switch to the world's best
> email. Get Yahoo!7 Mail! http://au.yahoo.com/y7mail
> > 
> > _______________________________________________
> > Synth-diy mailing list
> > Synth-diy at dropmix.xs4all.nl
> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy


      Make the switch to the world's best email. Get Yahoo!7 Mail! http://au.yahoo.com/y7mail




More information about the Synth-diy mailing list