[sdiy] Parts ID request

[John Loffink]

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
> 
> 
> 
> 
>