[sdiy] Dual/quad opamp bleed-through

[David G. Dixon]

...I think I'll do more or less the same thing as in the picture, but I'll
probably use a THAT 320 quad pnp for the two expos...

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C. V6T 1Z4
Canada
 
Tel 1-604-822-3679
Fax 1-604-822-3619
 
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> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of David G. Dixon
> Sent: Saturday, January 31, 2009 11:53 PM
> To: 'Dave Manley'; Synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Dual/quad opamp bleed-through
> 
> Hmm.  The key here is that the 3086 has no power pins, and the individual
> transistors can be well isolated from each other by grounding pin 13.
> It's
> the common power pins of dual/quad IC's which are the problem, I think, as
> Harry Bissell pointed out earlier.  There is simply no way to bypass the
> rails inside the IC.  I don't think there is much problem with two VCO's
> living side by side on the same pcb.  Indeed, it may be better that way
> than
> back to back on two separate pcb's, given the potential for inductive
> effects of the latter.  I also like the symmetrical layout.
> 
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> 309-6350 Stores Road
> Vancouver, B.C. V6T 1Z4
> Canada
> 
> Tel 1-604-822-3679
> Fax 1-604-822-3619
> 
> "PERFECTA FINGAMUS SERVIAT NATURA"
> 
> The information in this email and in any attachments is confidential and
> intended solely for the attention and use of the named addressee(s).  It
> must not be disclosed to any person without the writer's authority.  If
> you
> are not the intended recipient, or a person responsible for delivering it
> to
> the intended recipient, you are not authorized to and must not disclose,
> copy, distribute, or retain this message or any part of it.
> > -----Original Message-----
> > From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> > bounces at dropmix.xs4all.nl] On Behalf Of Dave Manley
> > Sent: Saturday, January 31, 2009 11:37 PM
> > To: Synth-diy at dropmix.xs4all.nl
> > Subject: Re: [sdiy] Dual/quad opamp bleed-through
> >
> > Here's another single board dual VCO - the Oberheim SEM
> >
> > http://www.sequencer.de/pix/oberheim/oberheim_sem_module_m.jpg
> >
> > The two VCO's are symmetrical and in the upper right of this image.
> > Voltage
> > summing at the top, two tempco's on top of a 3086 expo, two polystyrene
> > timing caps at the bottom (just above the 'de' in "image
> > www.sequencer.de".
> > No common parts, except the 3086.  Looks like good use of a ground fill
> > to isolate parts of the two VCOs.
> >
> > -Dave
> >
> > > I'm going to play devil's advocate and mention a few well known
> > > synths that have multiple VCOs on the same board: Moog Mini,
> > > ARP Odyssey, and KORG MS-20.  They don't share ICs, but
> > > they are on the same board.
> > >
> > > Do any of these synths have unintentional oscillator sync problems?
> > >
> > > -Dave
> > >
> > >> The first prototype of my dual VCO module had this same problem.
> > >> I then split the two VCOs onto separate boards with shared panel
> > >> controls.
> > >> This design still had sync problems. It was only after I placed the
> > >> boards at least 3/4" apart using standoffs that the syncing was
> > >> eliminated. This was with good de-coupling and hefty gauge star
> > >> wiring etc.
> > >> No shared ICs or even on the same board.
> > >>
> > >> Bruce
> > >
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