[sdiy] SSM2044 Filter schematic??

[john mahoney]

Yeah, I'm sure. The schemos label the Q81C as 1K Ohms, and the datasheet
says to substitute a plain 1K resistor if you don't require precision
tracking.

Thank you for the tempco tip, Philip.


Here are the differences between the SSM and Barry Klein circuits:
(1) Between pins 4 and 5, SSM specifies an 820 pF cap where BK uses a 470
pF.
(2) On the input to pin 2, SSM uses a 13K resistor versus 15K on BK's
circuit.
(3) Between pins 1 and 15, there is a pair of 200 Ohm res on each circuit,
but BK has 3300 pF caps in parallel with each of them (the SSM circuit has
no caps there)
(4) On the filter's output, BK places a 1K resistor on after the TL082. SSM
omits this output resistor, but it seems like it should be there -- this
establishes the output impedence, does it not?
(5) Finally, Barry Klien's circuit has pots/etc to send CVs to "Q,"
"frequency," and "Q rejection trim (optional)." SSM's datasheet simply has
inputs for "Q Control" and "fc."

I think I've identified them all. If anybody knows what differences those
changes will make, please speak up.

I hope this helps!
--
john


----- Original Message ----- 

> Are you sure about this?  In Chamberlain's "Musical Applications of
> Microprocessors," a VCO calls for a Q81, which is labeled in the schematic
as a
> 2k resistor.
>
> Ryan
>
> > I assume that the Tellabs Q81C is no longer available, and I'm not sure
what
> > to substitute for it, as it's a 1K device. The tempcos I see these days
are
> > 2K devices. Hmmm...
>