[sdiy] Q: oscillator bank

[David Cornutt]

I'm just now getting caught up on SDIY, so if I can follow up on a 
thread
that is a couple of weeks old...

On Nov 15, 2004, at 8:54 AM, Grant Richter wrote:

> This is exactly how the EML-101 was done. There are two uA726s, one 
> for the
> VCOs and on for the filter. But everything is linear voltage 
> responding.
>
>

Actually, in the 101, the 726s aren't used as matched pairs but as
individual transistors.  There are three expo converters (each using
one transistor in a 726) implemented: one for the CM2 bus, one for
the CM3 bus, and dedicated to the filter CV bus.
This obviously leaves one transistor in one of the 726s
unused, which gives the poor 101 owner at least some hope if
one of the transistors fails; if you do some re-wiring, you might be
able to get it working again by connecting to the unused transistor.


> It works, a bit fussy though.
>


More than you ever wanted to know about oscillator CV switching
on the EML 101: The CM2 bus is whatever is selected by the
"Control Mode 2" switch on OSC 2; this can be either the
straight primary keyboard voltage, or the primary keyboard
voltage added to the output of the oscillator control mixer.
The CM3 bus is selected by the "Control Mode 3" switch on
OSC 3; this can be the CM2 bus, the duophonic keyboard
voltage, or the duophonic keyboard voltage added to the
output of the oscillator control mixer.  There are a couple of
implications to this: Oscillators 1 and 4 don't have their own
exponential busses, so if you select something other than
CM2 or CM3 on their control mode switches, you are driving
them in linear mode.

As far as stability, though, it's surprisingly stable once you let
it warm up for a few minutes.