How to convert period CV to pitch CV

[Mark Smart]

> > Very interesting. Can you draw a schematic diagram of that part?
> 
> It's a pretty complicated circuit. I have the GR300 service manual which I
> got directly from Roland (you can still get these, they're about $20), and
> even it is a copy. I would be willing to copy mine for people, if they
> want, but it might be hard to read.

After I wrote this I realized that you were referring to the
second-harmonic suppression part only, not the whole thing. I can describe
it briefly:

There is an op-amp comparator which compares the input and output of the
sample-and-hold circuit (whose output is the voltage proportional to the 
string's period). If the output of the sample-and-hold goes to a higher
voltage than the input, the comparator activates a transistor which shorts
out the capacitor on the envelope follower circuit, causing its output to
go to zero. At least, that's the best guess I can make based on the blurry
schematic and the verbal description written by someone who speaks English
as a second language in the service manual.

That makes sense, because that won't happen in the normal decay of an
unchanging note, unless the second harmonic suddenly becomes louder than
the fundamental, causing a pulse to come in  between the pulses from the
fundamental.




________|________|________|____|____|________|________|  pulse train


    ___-|    ___-|    ___-|              ___-|    ___-|  Integrator output
__--    |__--    |__--    |__--|__--|__--    |__--    |  (=S/H input)

--------------------------------             ----------  S/H output
                                -------------

                                         ^
                                  right here, S/H
                                 output exceeds input

If this keeps happening over and over, it will cause the envelope
generator's output to go way down.




************************************************
*     Mark Smart                               *
*     Network Technician                       *
*     University Communications Inc. (UCI)     *
*     smart at medusa.nn.com                      *
************************************************