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Hz/V > V/Oct converter circuit?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Hz/V > V/Oct converter circuit?
I'm confused on the whole reverse-log-double-somersault-expo conversion thing and couldn't find a schematic on this, although I found the reverse circuit, V/Oct > Hz/V which I'm not really interested in. I suspect it's a version of the 2-transistor converter circuit I'm familiar with, but that could be totally off-base. Anyone have a link/schematic for this? I just got an MS-20 and it sits so nice under my dotcom I'm kinda wanting to get the dotcom to play nice with the Korg's keyboard sometimes. The dotcom and MS-20 are fun to patch together, they're SOOOO different. Korg sold a few MS-02 sidecar boxes that had the circuit in it I'm looking for, as near as I can tell. That box would be handy but I guess they're rare and expensive.
yeah the MS-02 is what you are talking about.
I have one and they are sooooo handy for many different tasks including log amp, antilog amp, adding amp, and gate inversion (s-trig <=> v-trig)

I know on elby-designs they had a mock-up of what looks like an MS-02 clone for euro rack. Dunno when it is coming out tho.

The schematics for this circuit have been available for a long time and they are pretty simple. No reason why you couldnt DIY it.

Thanks Chinard!
The log amp section is exactly what I was looking for and indeed uses 2 transistors for the conversion like I was thinking. Too bad there aren't more of these boxes around (the MS-02). It looks very handy to have if you own an MS-20 or something similar.
Whoa, this is really intriguing as I have more Hz/V stuff than a sane person should have. So am I correct in understanding that the "log amp" section of this schematic will allow Hz/V instruments to properly play/be tuned when receiving V/Oct. signals (such as from a sequencer)?

If not, I'd love some clarification of the purpose of these circuits. Thanks much for your time!
The MS-02 does pop up once in while. The ones I have seen has not been that expensive (550-600 usd). With a little patience and a little luck you may find one. It IS a very nice addition to your MS-20.
valis wrote:
If not, I'd love some clarification of the purpose of these circuits. Thanks much for your time!

heres the manual for the MS-02

overview of functions is pretty straight forward.

Log Amp = Hz/V => Oct/v
Antilog Amp = Oct/V => Hz/V
Trigger processor = Gate inversion for S-Trig to V-Trig format.
Multiples = self-explanitory
Adding amp = useful for offset scaling in Hz/V systems. (raising or lowering pitch)
Oct/V is dead easy cause you just add or subtract even voltges for every octave, Hz/V is a bit more complicated as it is linear instead of exponential. Either way the adding amp takes care of this.

Now if all you are interested in, is going from oct/v => hz/v, well the good news is you do not need a MS-02!!!

Two rather interesting guides for adding a Oct/V input to an MS-20. %20V/Oct%20CV%20Input%20&%20Trimmer

I have also done Oct/V=>Hz/V with the Attenuators on a Moog CP-251. The sweet spot seems to be around 7. Play around with tuning until you get decent tracking.
This was actually documented on the old 'moogspace' forum in a document called 'lord of the ringmod' It seems that the moogerfooger ringmod had an Hz/V triangle oscillator as its modulator, and this is how they recommended pitch tracking when used with a voyager.
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