Hz/volt - Volt/Oct converters

[wvreyywvreyy]

YOYOYOIYO!

i was wondering what you folks knew about hz/volt to volt/oct converters for synths. Some of the converters i have checked out are the korg ms-02. but that thing is REALLy expensive just for a converter. I was wondering if you guys knew of any other good converters for this operation, or if any of you guys had built one in the past.

[Jyoti]

Sorry, the only straight CV converter I can think of is the one you mentioned.

BUT

Have you considered using a Kenton unit:

http://www.kentonuk.com/digital_interfaces_converters/midi_cv_converters_extras/prosolo.html



That can do the Korg CV output. At least the Korg would then be playable from MIDI units. And then, maybe if you got a CV -> MIDI, you could play the Korg from non-MIDI synths?

Sorry, not much help, I know!

[wvreyywvreyy]

hrmmmmm
THANKS FOR REPLYING!

imi confused as to what this thing does. basically im just trying to incorporate my hz/volt synth with a volt/oct synth. can this do that?

or PLEASE explain to me what it does. I have a hz/volt cv output on my synth

[Jyoti]

I'm presuming you also have Hz/V CV and gate inputs too?

That Kenton unit will let you play your Korg from any MIDI source. It translates MIDI -> Korg CV/Gate.

It will also let you play V/Oct synths via MIDI.

Thus, you could have both your CV/Gate synths playing together if you don't mind using MIDI.

The only link I found for easy V/Oct to Hz/V is here:

http://www.korganalogue.net/korgms/mstt.html

BUT - I've never owned an MS10/20 so I have no idea if the tip there works.
Use at your own risk!

[EdisonRex]

That's a good reference, Jyoti, I hadn't seen that before.

wvreyywvreyy, is it an ms-20 or ms-10 you have, or another Korg, or is it something else? Also, do you have any MIDI at all?

The Kenton units (in general) take MIDI input and convert to either Hz/V or V/Oct **(not both at the same time on the same MIDI channel though)** So for instance my Kenton Pro2000 outputs Hz/V for the Wretch, and V/Oct for the M5N. But on two different MIDI channels.

Without using MIDI, the problem is one of linear to exponential conversion, or exponential to linear conversion depending on the controller (ie which synthesizer you want as the master). Of course this has been done many times, a good schematic is Magnus Danielson's one here but it's a common enough circuit.

Assuming you don't want to build anything, the most common item in the bag of tricks you'd use for modular use is a VCA, preferably one with switchable linear or exponential response. I've seen references to dotcom's VCA, but I think there are plenty others out there. You'd use the VCA as a control voltage source, fed with a constant (offset DC) voltage on the "signal" in, and take your V/Oct "pitch-control" voltage to the "control in" on the VCA with it switched to exponential mode. The VCA would then convert the exponential (V/Hz) control voltage to linear (V/Hz) which would appear on the VCA's "signal out". You probably have to adjust the control voltage level to get the scaling right. What you have to remember is that the VCA will be running in DC mode (so if you have an AC coupled VCA then this won't work), and you're using the VCA's control input as the converter.

Oh, yeah. This has been discussed as well, here, that the inverse of exponential is logarithmic, so technically to convert linear to expo using a VCA you have to do an inverse exponential (or log) conversion. Some VCAs can do this as well (Ray Wilson's is mentioned in the referenced thread). Probably best to read the thread.

[Cat-A-Tonic]

Elby-designs supposedly have a Hz/V - V/oct converter, but it has yet to be released.

That VCA trick sounds great if I can get it tuned right.
Thanks for the advice. I'll try it with my TM-3 Oscillators.

[Rhythmicons]

Do you think this module would convert the CV from an Etherwave Plus Theremin and allow it to control the New Taurus Pedals which are Hz/V?

Eric
Rhythmicons

[phinland]

Are you aware that the MS20 will take a log input and convert itself to lin without any conversion?

Citing from http://www.korganalogue.net/korgms/mstt.html

"I can hardly believe no one knows about this already. It is possible to control an MS-20 from a V/Octave keyboard or MIDI/CV converter without a special interface. If you don't believe it, try it . .

When I first got my MS-20, I noticed that the filters don't track the keyboard at all. I plugged the keyboard cv to the filter cv in, but then the filter tracked the keyboard slowly in the lower octave, then went screeching off in search of tweeters to kill! I soon realised that the filter was tracking exponentially. I looked at the schematics and sure enough, both the VCO's and the VCF's have exponential converters on the modulation inputs. (You can tell this is the case, because the synth also goes radically out of tune when you plug the kbd cv to the TOTAL input, and wind up the MG / T.EXT knob in the FM section.)So, if you stick a V/OCT input into the modulation inputs and adjust the MG level for correct scaling, it all works and the filters track too.

Here's how you do it:

1. Plug the performance wheel into the keyboard cv input (middle, right) to disconnect the keyboard.
2. Plug the V/OCT cv from your MIDI/cv converter or another synth into the Total jack (top left).
3. Plug the s-trig. from your MIDI/cv or synth into the MS-20 trigger input.
4. Play a note on your MIDI keyboard or the controlling synth, and adjust the MS-20 performance wheel until you get a sensible pitch.
5. Adjust the VCO mod. levels until playing an octave on your MIDI (or other synth) keyboard gives an octave out of the MS-20. Then adjust the MS-20 performance wheel to coarse tune the MS20 and use the tuning pot to fine tune it.
6. The filter mod level pots adjust filter tracking in the same way.

You lose use of the performance wheel on the MS-20, but that's not a big problem if your MIDI/cv converter or your other synth has pitch bend. You will need a v-to-s trigger converter (i.e. the MS-02 Interface) to control the MS-20 from synths without s-trig. outputs, but they're simple to make (two resistors and an NPN transistor, plenty of circuits posted elsewhere).

I don't have the MS-20 in front of me, so apologies if the names of pots and jacks are not exact. Believe me, it does work!"

(from Steve Ridley)

Somebody else added:

"Beware of one thing... the VCF's are twice as sensitive as VCO's so that you must bring the VCF's mod pots to about 5 where as you would have the VCO's mod pot to 10. I think this can confuse some people the first time they fool around... Actually, if one wants good VCF tracking one has to be careful in trimming..."

[thermionicjunky]

http://www.kentonuk.com/kenton/pcb_project/k1-cvhzm.html

[ai]

PAiA has an adapter board available for their MIDI/CV module. Maybe they'd sell you one separately...

http://www.paia.com/midi2cv.asp