[sdiy] Parts ID request

[Harry Bissell Jr]

Could be an array of JFETs tuning in the standard
shunt mode...

H^) harry


--- John Loffink <jloffink at austin.rr.com> wrote:

> Hmmm...I traced out one op amp stage of the
> rectangular potted can.  It is a
> cascaded 90 degree phase shift network, but the
> normal connection from + op
> amp input to resistor to ground instead connects
> directly to the rectangular
> potted can.  18K feedback and negative input
> resistors, .002 cap to positive
> op amp input.
> 
> The potted can is obviously providing a variable
> resistive element to
> control the corner frequency of the phase shifter. 
> This could be done
> through switched capacitor techniques, as well as
> several others. 
> 
> John Loffink
> The Microtonal Synthesis Web Site
> http://www.microtonal-synthesis.com
> The Wavemakers Synthesizer Web Site
> http://www.wavemakers-synth.com
> 
> 
> > -----Original Message-----
> > From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-
> > diy at dropmix.xs4all.nl] On Behalf Of John Loffink
> > Sent: Monday, February 14, 2005 9:35 PM
> > To: 'harrybissell'
> > Cc: synth-diy at dropmix.xs4all.nl
> > Subject: RE: [sdiy] Parts ID request
> > 
> > > -----Original Message-----
> > > From: harrybissell
> [mailto:harrybissell at prodigy.net]
> > >
> > > I doubt very seriously they are switched
> capacitor filters... the age is
> > > too old... they are surrounded by 741 opamps and
> maybe a TTL chip ?
> > >
> > > 5% resistors... etc.
> > >
> > > I'd guess they were homemade modules... maybe
> expo converters that
> > > would benefit from the epoxy potting.
> > >
> > 
> > The socketed chip way behind the round can is just
> labeled "381."  I'd be
> > surprised if the cans were exponential converters
> since even the VCOs in
> > this unit don't have potted elements.  I wouldn't
> say these are too old to
> > be switched capacitor elements - the theory was
> quite well known by the
> > mid
> > 1970s.  You do have a point though about all those
> 741 op amps and 5%
> > resistors around the cans.  I'll trace out the
> circuit for one of the
> > circuit "legs."
> > 
> > > (good cop)
> > >
> > > Are they YOUR modules ?  If you posted really
> detailed pictures of both
> > > sides
> > > I'd be willing to try and trace the schematic to
> the point of implying
> > > what is
> > >
> > > inside...    ~or~
> > >
> > 
> > I will be tracing out the circuit myself in the
> next few weeks.  There are
> > eight circuit boards and many interconnections for
> the complete circuit.
> > Once the circuit is traced I will be scoping it
> out under power to see
> > what's going on at each pin.
> > 
> > > (bad cop)
> > >
> > > we could send them downtown to see the "old
> crow" who has a way of
> > > getting the information out of stubborn epoxy
> modules like you...
> > >
> > > ...but it aint gonna be pretty...
> > >
> > 
> > Now that would be a last resort... :-)
> > 
> > John Loffink
> > The Microtonal Synthesis Web Site
> > http://www.microtonal-synthesis.com
> > The Wavemakers Synthesizer Web Site
> > http://www.wavemakers-synth.com
> > 
> > 
> > 
> > 
> > 
> 
> 
> 
>