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.]