Voyager -> VX-351 -> Korg MS20

[punkdisco]

Hi - finally got my signed AE Voyager last night from Turnkey so very happy. The lights look incredible; really surprised this has never been done before on a synth (to my knowledge).

Anyway, I am considering a VX-351 to interface into my MS-20. I know the MS20 used Hz for keyboard CV input so playing one from the other is tricky without serious patching. However, what about all the modulation options on the MS-20? Will the two synths be able to modulate each other okay?

I guess this is more of a MS-20 question but was hoping someone on here will have such a setup so advise accordingly..

btw, thanks for all the guidance over the last 2 weeks. It was a little nerve-racking making such an extravagant purchase..

[Qwave]

you can connect them, but you will experience strange things because of the different voltage to pitch ratios.

Lets saw you use the Voyagers LFO to drife the MS20 oscillators.
You will notice, that the lower and upper pitch max of a vibrato will not be in the same musical distance from the unmodulated pitch. Use a square wave to check this. And if you change the pitch of the MS20 oscillators from the MS20 keyboard at the same time the modulation amount will change. Sounds strange for all usefull playable sounds except for FX sounds.

[peter ripa]

what if you use the 251 junction to split the signal, invert one of them with the 251 and attenuate to taste and the modulate the signal with its negative self via the VCA in the ms20? im not home now so i cant try,perhaps its the other way around, modulate the signal with itself

are you sure about this qwave? i thought it was only the main CV in that had the exponential behaviour and that the other ins were normal. the "modulate" in is normal V/oct so you can control the pitch of the ms20 if you plug it in the "modulate" hole, dont remember the name

[punkdisco]

Thanks for your replies guys..

"are you sure about this qwave? i thought it was only the main CV in that had the exponential behaviour and that the other ins were normal"

This is what I recall, hence the question. I'll check on Analogue heaven but ill post the answer here so the thread 'has closure' as they say in the US..

Thanks again,

[baward]

Anyway, I am considering a VX-351 to interface into my MS-20. I know the MS20 used Hz for keyboard CV input so playing one from the other is tricky without serious patching.

As a slight aside, MS-20 users might want to know that you are not restricted to using one scaling with the MS-20. This is from my Korg website at 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!"

Regards,
Ben

[peter ripa]

yes thats how i remembered it but was too lazy to check your site
thanks ben

[punkdisco]

I got bored of trying to research the answer so I just popped back to Turnkey and got one Will let you know how I get on over the weekend..

Thanks for your replies.

[punkdisco]

Hi - a while back I asked about a Voyager/XV351/MS20 combo and if it would work. We decided that it should be okay as "only the main CV in that had the exponential behaviour and that the other ins were normal".

Anyway, I FINALLY got a stand and things rigged up properly so I could have a play last night. Works totally as expected which is great..

There is one issue regarding temperature. Basically, because of the Linear/Exponential mix, there will be a bit of 'drift' with temperature. If you only plan to do modulation stuff which is not really 'tuning important', you should not every notice this drift. Even if tuning is import I think it will just become unstable with temperature change so once warmed up, again not noticeable..

I don't really understand all of this so here is a reply from Colin Fraser (P3 Sequencer designer) but in summary, it does work..

>>

I think there may also be temperature compensation issues this way too.

The typical converter circuit used in an analogue synth to convert from a linear voltage to an exponential current relies on certain properties of a transistor which are temperature sensitive. I'll not bore you with the formula...

Normally this factor would be cancelled out, either by using a resistor with the opposite temperature sensitivity to the transistor, or by heating the transistor to a fixed higher-than-ambient temperature. But in non-critical applications, cheapskate synth builders will leave temperature compensation out.

In the MS20, there is an exponential converter circuit used for modulation of the VCOs, but a linear input to the converter circuit is used to control frequency, from the hz/v keyboard circuit. The linear input is not sensitive to temperature. The expo input is, but this will only cause a scaling error in your modulation signals, so you wouldn't normally notice.

If you use the modulation input to exponential frequency control, you will have to rescale as ambient temperature changes.