[sdiy] The never ending ASM-1 VCO troubles :-)

[Neil Johnson]

> > Check the reset transistor is connected correctly -- I had a similar
> > experience with my VCO, only to find that the reset transistor was
> > connected thw wrong way (pinout error on PCB), such that the LM311 was
> > feeding current into the capacitor...Doh!!  Fixed it, works a treat.
>
> Actually, the PCB is correct - put only if you use the PN4391 and not
> the 2N4391. I think I put that one on the web.
>
> It took a carefull look at the PCB and the datasheet to figure out.

Sorry, what I should have said is "...on MY VCO PCB...", as-in my little
MSM-VCO (see http://www.njohnson.co.uk), which is based on the same
integrator/reset circuitry as the ASM-1 VCO (and a whole host of other
VCOs...so much for originality :-)

But the failure mode is the same -- get the tranny the wrong way round and
the VCO will sit there oscillating at some high freq. all by itself, with
very little effect from the expo current.

Hope this helps,
Neil

--
Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
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