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a couple Voyager mod ideas...

Tips and techniques for Minimoog Analog Synthesizers

Re: a couple Voyager mod ideas...

Postby till » Sat Jul 06, 2019 10:36 am

ummagumma wrote:...and guessing at how the digital pots feed the analog ( I assume? ) mixer
...

In fact the mixer is not a normal mixer but a array of summing VCA.
The knobs are just doing a drop in voltage.
A multiplexed A/D measures every pot voltage many times a second.
The digital numbers representing the knob position are only used, if there is a certain amount of change since the last loading of a patch. Otherwise the stored virtual knob position number is used. This virtual or real nob position number is than used by a multiplexed D/A to send to the nalaog sound generating board. Also all other informations like MIDI or keyboard notes are D/Aed and sent to the analog board. The analog board got 57 CV controlled parameters. Every continues knob on the front panel is a CV. And there are switched that are controlled by the digital board.
So even the resonance and the individual stages of the envelopes are CV controlled on the Voyager.

So the mixer knobs are in no way connected to the mixer electronics. The mixer just receives more or less steady analog CVs generated from the digital board (by the knob position or the stored patch data). So the mixer knob of VCO 1 is in fact a VCA. And all the mixers channels VCAs are then summed together in a static manner.
All this mixer thing is more or less like on all synths with digital patch memory and real analog sound generating.

You can do a break-out of the signal of the VCA channels of the mixer and change it by some Op-amps to get the right level to mix their signal in a CP3 like mixer (that would be set on a fixed all open position to use patch memory). And then lower the CP3 signal and feed it into the external audio in of the Voyager. I would do this only with the oscillators signal and the noise. The external signal would be untouched on the Voyager's mixer.

Finding the needed points to get the signal would be no problem (but will take some time) if you got a scope and take the needed precautions when working on running opened electronics.
keep on turning these Moog knobs

Sequence:
Prodigy * Minimoog (1979) * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog reissues with MUSEs * One
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Re: a couple Voyager mod ideas...

Postby ummagumma » Sat Jul 06, 2019 11:21 am

wow, thanks for the detailed explanation!

in light of all that, it wouldn't be much different than just using the mix out/insert to run thru a CP3 style circuit/effect

I was hoping to get individual OSC/noise/ext level control, thru the CP3. Similar to the Grandmother/D mixers & how they interact

Actually I guess you WOULD have control over the individual OSC/noise, but then they would be summed and fed into the EXT. And you would not be able to use the EXT on its own, with other sources?

ps your op-amp dropping note makes me think that perhaps the mix/out I have been feeding my FX needs to be attenuated
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Re: a couple Voyager mod ideas...

Postby ummagumma » Sat Jul 13, 2019 7:51 pm

I am somewhat embarrassed to admit, that I have been using the wrong mix out/insert cable, in my efforts

I built the mix out/insert cable described in Knobtweaks: which sends the voyager signal back into itself, and acts as a breakout so you can tap the signal and run it through external effects. I have been feeding this into various devices, and returning it via the EXT in, blending it with the original OSC's in the voyager mixer

Well, just using a regular Y stereo-->2x mono cable lets you run the voyager OSC's through effects, and back into the synth, with no need to do any of that. Or use the EXT in. No wonder I was dissatisfied with the sounds I was getting....I was only blending in effects via the mixer, and not modifying the internal OSC sound at all

( the apple hit me on the head while I was trying to attenuate the mix/out signal via the CP251/XL front panel, to bring the signal down & be more "guitar pedal" friendly. I realized I could just feed a Y cable through the pedal itself )
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Re: a couple Voyager mod ideas...

Postby Markyboard » Sun Jul 14, 2019 10:32 am

Don’t be embarrassed because it’s not quite what you say. Using the Knobtweak cable provides 2 paths for the oscillators to get to the filter; The mix output using the tip (send) /ring (return) is direct (I.e. no feedback on its own) and the other path tip/send only which is fed back through the external input creating a mixer feed back loop. Once the mixer starts feeding back the direct signal is also affected. It’s not like it’s bypassing the feed back loop. So you can’t really claim to be mixing a clean signal and a feedback signal. Yes they blend but not the way you’d expect. And it’s very much dependent on the mixer levels which affects both paths (send/return and external input).

Using a conventional Y-cable is perfect for Integrating external effects so good on you for resolving your issue. Btw the original mini feedback trick uses the post filter output signal. So you need to connect the L/R output or the headphone output to the external input. Not sure how much goodness you get from just mixer feedback as provided by the knobtweak cable.
Last edited by Markyboard on Sun Jul 14, 2019 2:37 pm, edited 1 time in total.
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Re: a couple Voyager mod ideas...

Postby ummagumma » Sun Jul 14, 2019 11:36 am

ah, that is interesting!

thx for the info. have not tried the headphone loop, due to the warnings of using a mono cable vs stereo/balanced

ps using one side of a stereo cable would only give you a L or R; I'll check if the Knobtweaks mix cable would sum LR together

have been using the spacing control a lot in my patches, and stereo out
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Re: a couple Voyager mod ideas...

Postby Markyboard » Sun Jul 14, 2019 11:49 am

DO NOT use that knobtweak cable in the headphone jack unless you can separate the tip signal from the ring. Remember these are shorted together at the TRS plug. A standard Y cable is what you want. Just leave either of the mono plugs disconnected.

Btw modulating the spacing control... 8)
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Re: a couple Voyager mod ideas...

Postby ummagumma » Sun Jul 14, 2019 3:51 pm

ok good to know...I may test to see if summing the LR headphone signals together makes much difference, in feedback

if so, I can make a cable specifically for that

-->if there is any stereo modulation ( panning/spacing etc ) it might be weird with only 1 channel. Or useful, I suppose, depending on the patch

I REALLY want to add a spacing CV in, under the filter CV, on the XL front panel

I think the Matriarch has some more advanced spacing CV too

thx again!
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