Doepfer

Hi Jason,
	A few minutes experimentation soon highlighted likely problems to be
encountered when trying to do this. The top range of the A-111 starts
at 1046Hz (and not the octave above this as I previously guessed):
feeding approx 3.75V into CV1 to get 14,100Hz using the fine tune is
just about do-able. To use CV2 pot to attenuate +/-5V to give +/-10mV
requires adjusting it to 1/500th of its total movement ? I didn?t even
try: instead I used 2 A-138 linear mixers chained together. I was able
to modulate the A-111 using an LFO, but at these frequencies I could
barely hear it/barely hear the small pitch changes due to the
modulation. I then noticed my tiny +/-10mV signal from the LFO had a
small DC offset, so I measured the A-138 output with 0V input ? I have
3: one gave  0V out; another 6mV, last one 12mV. These offsets are
broadly consistent with the op amps used in the A-138 circuit:
normally they are not a consideration, but for such a demanding
requirement would require even more fiddling to compensate for.
Similar effects ?further down the chain? in other circuits are likely
to be encountered, and so this is the point at which I gave up! I
think you will have great difficulty doing this, if at all.

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.]


> Hi Jason,
> 	Interesting challenge! I did some quick calcs: say the note C at
> highest range setting (=4) of  A-111 is 2093Hz (if I?m an octave out,
> then just +/- 1V as appropriate), then to get 14000Hz, input voltage
> is 2.74V, and for 14200Hz it?s 2.76V ? that leaves just 0.02V=20mV to
> play with! For comparison, a standard semitone?s worth = 1/12 V =
> 83mV, i.e. 4 times as much. Your requirement thus seems quite
> demanding! Initial thoughts are that you will probably need at least a
> pretty good voltmeter to do this, if not a frequency counter. You
> could input 2.75V to CV1, and then try setting CV2 input pot so that
> the usual A-100 (nominal) +/-5V range (from LFO/whatever) is
> attenuated to +/-10mV, assuming it?s possible to adjust the pot to
> give you that (due to the exponential nature of the normal, i.e. not
> the ?linear FM?, input the centre frequency won?t be quite at this
> value, but with such a narrow, non-standard range, I suspect this is
> not of much concern?). I?ll have a quick play tonight, and if I come
> up with anything else, I?ll let you know.
>