Doepfer

Got a note from Dieter last night, who saw these listings and he 
went into the theory behind the Shifter and how it cancels out the 
second sideband to isolate the sum and difference.  Much as I've 
always heard its done, by [hase cancellation using the 90 
degree output of a quadrit. oscillator.  It's a very complex circuit.

So....Dieter does read these listings (HELLO TO DIETER...YOU 
ARE A VERY NICE GUY AND A BRILLIANT DESIGNER).  So, 
watch your P's and Q's in here, guys...who never know who's 
lurking!!!

best,

Peter





--- In Doepfer_a100@y..., "stinchcombe_t" <tstinchcombe@q...> 
wrote:
> Peter
> 
> > if you can get to the scanner, let me see the schemo, if you 
can.  
> > Dieter needs not worry - for $170 for the completed module, 
> > there would be little reason to attempt to replicate it from 
scratch 
> > - that would end up costing someone a lot more $$!.
> 
> 	Had a quick look at my 'scribblings' on the 126 last night -
> unfortunately I have only drawn out a small part of it neatly, but 
if
> I get time over the weekend I'll draw some more out tidily (and 
then
> see if I can sweet-talk our secretary to let me use her scanner 
in
> works time...). The quad osc uses the 2 VCAs in a CEM PA382 
chip
> (exponential response). The circuitry summing the shift CV 
which is
> then applied to the 382 includes an 'offset' preset, and this 
should
> thus be setting the lowest frequency of the oscillator. From my 
rough
> calcs, assuming the gain of the VCAs is 1, the oscillator would 
run at
> approx  15kHz: estimating the gain at the actual voltage applied 
for
> max and min shift gave me frequencies of 6.5kHz and 30Hz, 
which tied
> in well with the measured values on my 126 of 5.8kHz and 
57Hz. Thus
> reducing the lowest shift possible may be simply a matter of 
twiddling
> this preset a bit (although the osc is AC coupled to the 1496 
chips of
> course...). This also suggests that it would be nice to see the
> service manual for the 126 anyway, to establish just what 
Doepfer's
> set-up procedure with respect to this preset is (and of course 
this
> will include the schematic anyway...) - it's a real shame that its
> priced just a bit above what I'm prepared to pay, just for the 
sake of
> having it, but I could be even more tempted if Doepfer made it
> available on a CD, 'cos then at least one could use babelfish  
to get
> around the language problem!
> 
> Tim
> 
> [The views expressed above are entirely those of the writer and 
do not
> represent the views, policy or understanding of any other 
person or
> official body.]