Once again The Trident!

[jh.]

> Message text written by Haible Juergen
> >
>         >The Moog oscillators that used a common expo converter for
> multiple
>         >oscillators, was that voltage or current?
>
> Current.<
>
> Hi Juergen:
>
> Sorry to differ on this, but the 901A drove multiple 901B's with a
variable
> voltage.

Yes, you're completely right. And I have used this as an example for
linear detune so often that I actually forgot to mention it when Grant
asked.
I was referring to much later circuits, I think the Multimoog used
one transistor array with 3 expo current outputs for 2 CCOs and
a CCF. And there was another one which shared an expo converter
for one CCO and one CCF.

Thanks for reminding me,

JH.






The op amp driving the diode string in the expo converter had an
> output stage consisting of a PNP transistor with a resistor from the
> emitter to +12V, the base voltage of the transistor was brought out to the
> edge connector on the PCB, from there it went to typically three 901B's.
> Each 901B had a PNP transistor matched to the one in the 901A, with a
> resistor from the emitter to +12V, the transistors were all matched, so
the
> same current (and hopefully the same frequency) should be delivered by
each
> one.  This arrangement was part of the reason the 901 series VCO's drifted
> so much, the transistors were on separate circuit cards in separate
> modules, temperature differences between the transistors would alter the
> forward bias of each one, and though there was resistive emitter
> degeneration, it would still create some degree of linear frequency
offset.
>
> The input op amp used a normal resistor instead of a +3500ppm tempco, so
> the scale factor drifted also.
>
> Terry Michaels