[sdiy] Cat SRM 2

[Microtonal]

There are schematics of the SRM on the web, though I can't remember where I
got them from.  I can email them to you privately if you wish.  They appear
to be current as they include the LFO delay circuit.

As far as I can tell there's no difference between an SRM and an SRM II
except perhaps the internals.  The last feature added to the SRM is the LFO
Delay.  My Cat SRM and user manual say nothing about a "II" model number but
have this feature.  Interestingly, the manual does not include the LFO delay
in the patch sheet so this would be the period when that feature was added.
The model number on the rear serial number plate is "1853."  This unit was
purchased in June 1980.

The SRM is not an Odyssey in a different box.  This myth continues to be
perpetuated without any facts.  If you look at the architecture and
features, they're too different from an Odyssey to be a copy, but they are
closer to an Odyssey than to a Minimoog.  You could say that the Cat was
inspired by the Odyssey, but to say that it is a complete knock-off ignores
the multitude of differences noted below.

Some differences:
SRM:  No pink noise
SRM:  No ring modulator
Odyssey:  No cross modulation by VCOs
SRM:  2x3 way FM switches, Odyssey 2x2 way FM switches
Odyssey:  No AR FM of VCOs
SRM:  Sine/DC pulse width modulation, and only on VCO1, square wave only on
VCO2, Odyssey has sine/ADSR modulation
Odyssey:  no suboctave waveforms on VCOs
Odyssey:  no triangle waveform on VCO1
Odyssey:  switch selection of VCO waveforms and noise/RM with mixing
sliders, SRM has slider per VCO waveform and noise
SRM:  no HPF
SRM VCF:  2 FM switches and levels instead of Odyssey's 3, but has separate
keyboard tracking knob
Odyssey VCF:  no modulation from VCO1
Odyssey:  no LFO sine modulation delay
SRM ADSR trigger source/repeat is 3 way switch, Odyssey is 2 switches
SRM:  no AR trigger source selection, is always keyboard
SRM VCO1 Audio on/off switch to filter, when using at low frequencies to
modulate VCO2 or the filter or used as S&H source
SRM VCA has a single volume control and ADSR/AR/bypass mode (no envelopes)
switch, Odyssey has intial gain and AM amount level/switch
SRM S&H source is noise or VCO1, Odyssey has 2 switch selections and sliders

Another myth:  Arp's lawsuit against Octave-Plateau put them out of
business.  They are still in business today as Voyetra.  Arp is long gone...

John Loffink
microtonal at worldnet.att.net


> Hi all,
>
> I'm on the scrounge... has anyone got a schematic for a Cat SRM 2
> please? I have a sneaky feeling its an Oddy in a different box, but the
> keyboard scanner looks way different.
>
> Regards,
>
> Tony Allgood  Penrith, Cumbria, England