Moog Music Forum

here's what I am trying to accomplish - I want to patch the pitch CV out from my Arturia Minibrute into the pitch CV in on my Slim Phatty so that the notes from the SP match the MB. The MB's voltage range is 0 to 10v and the SP is 0-5v. I have been playing around with the CP-251 and I can attenuate the pitch out of the MB to match a note up, but it doesn't track accurately up the keyboard - way off!

What is the simplest way to handle this?

also, can running 10v into moogerfoogers/cp251/SP damage them?

For now the simplest i'd say go midi !

But more to come tomorrow, especially regarding the original question

kingnimrod wrote:also, can running 10v into moogerfoogers/cp251/SP damage them?

Short answer, yes. Attenuators are pretty simple. 50k linear pots connected to 1/4" jacks. I'd say, either buy some, or build them if you can. Also, the new Moog stuff is .97 volts per octave, not 1 volt per octave as is standard. I'm sure someone else can offer some advice regarding that issue.

The SP manual says pitch voltage goes from -5v to + 5v, which makes more sense since 0 to +5v is only 5 octaves of pitch change.

So what's the best way to shift a 0 to 10v source to -5/+5?

Offset it by -5. Simply math applies.

In the case of the LP's (or SP's) CV Pitch input, negative values are... um, valid.

Most synths have an oscillator frequency range from m to n where 'm' is the lowest frequency that can be played (20 Hz?) and 'n' is the highest note played (tens of thousands of Hz.). In the 20 Hz example, you will hear clicking as if you were listening to a LFO running a square wave at a moderate rate.

The OSC range (8' for instance) added to the keyboard voltage (0v .. 3v in the case of Phatty's 3 octave keyboard) added to the position of the keyboard per octave up down keys = a voltage that is given to the OSC.

For that matter, you can run a low bassline from the Arp within the Phatty, then offset it by taking a 3V (with two D cell batteries for instance) to transpose 3 octaves in real time. Play the Arp at a higher range, or kick the OSCs to 2' and put a negative voltage to Pitch CV (noting polarity properly) and you'll transpose down.

The opposite applies as well. You can play an analog sequencer into Phatty through the Pitch CV, then transpose by pressing a key on the keyboard. The last key pressed is what the OSC begins with. Of course you can't hear it because the VCA is completely closed normally. It's handy to transpose sequences in this way but under the covers, it's simple voltages being summed together and negative is certainly valid.

If the resulting voltage is out of range, you might just get the lowest frequency, the highest frequency, or nothing at all. In the Voyager, overvolt applied to WAVE, for instance, silences the OSC. In the MInitaur, voltage which is too high for the OSC (since it's limited) continues to drone the highest standard frequency.

I wouldn't suggest plugging a 120V AC or a 50V DC power source into any CV, but mixing and summing voltages in the single digit ranges is very common. Any of you guys into MU modular should have a look at this: http://www.stgsoundlabs.com/products/mixer_mu.htm With it you can precisely dial in a given negative or positive voltage source in addition to mixing waveforms and then offsetting them in either direction. Take it further and get this: http://synthesizers.com/q123.html With it you can dial in/transpose CV by quantized intervals; of course you'll need to negotiate the fact that some Moog equipment is not 1V per octave precisely; exception being the Tribute LP which has a pot on the incoming CV (so I'm told) and Voyager analog boards mod'ed with the trim pot in R47.

right, but what off-the-shelf solution can I use to do the offset? Either box or eurorack module.

Not familiar with Euro, or at least I'm not familiar with what is out there. Doepfer or the guys that make those arcade push button modules may have some voltage offset modules.

But that's not your problem. Offsetting the voltage isn't going to solve your scaling issues; it's more a matter of Volts/Octave which is the 'standard' and I'm assuming that Minibrute does 1V/oct. There's another standard which is Hz./Volt but it's not seen much (from an interfacing perspective) these days.

I've read postings here of something like .97V / octave but I don't believe any of it. Rather, it is most likely tolerance in components and the fact that Moog doesn't take any efforts to quantize incoming voltage. Which make Pitch CV input ONLY good for things like ribbon controllers, analog sequencers, or external LFO (e.g. send in voltage which varies -/+ .08V for a nice vibrato). I say "ONLY" because that is quite a bit of functionality.

Who don't you just use Midi between the two like suggested above? Regardless of CV scaling, you should be able to do dead-on doubling, or offset by a fifth (via tuning), etc.

Can't use MIDI because there is no MIDI source.
In my case, I have a CV source that puts out 0v to +10v for pitch, vcf, and vca, so I would just like to find a simple way to offset this by —5v to safely use with the SP (the manual says damage will occur by exceeding +5v). I've used this CV source with the Mooger Freqbox and Lowpass Filter and it seemed to work fine, but on reading their manuals they also state not to exceed +5v.

Oh, I understood you were playing FROM Minibrute and wanted to have Slim play the same notes. My mistake.

I'm curious about the 0..10v specification you mentioned. Where did you see this documented? I do know that some of the Euro gear will range from 0..10V but typically that is for modulation control. If you have a multimeter, do this:

1/4" jack with red lead on tip, black on sleeve. Set your octave range on the Brute to the lowest, measure the lowest note, check an octave up, continue at different octave ranges.

I'd be interested to see how it reads.

On my Voyager Old School, the KB pitch is absolute, which is to say that it outputs the 3 octave range regardless of footage OSC positions (as it should do). On my Phatty with CV out, the voltage very much varies based on the octave buttons and you can in effect, slide the positioning of the keyboard virtually across a much larger voltage range. Your MB should do something similar.

I read in the documentation that you've got a choice of 5 positions for the 2 octave keyboard. So the range is really just 7 octaves, the lowest of which is likely unusable. And I didn't see any footage controls on the panel, likely because there is only a single OSC so no need to offset them, and sub-osc is fixed.

Kingnimrod is using a Minibrute, I am just piggybacking on his thread for some answers.
In my case it's a 1980's vintage Lyricon Wind Driver, so 0v to +10v is correct and standard for the time. It works perfectly with the Minimoog D, original SEM, Arps, etc., but I only recently noticed the –5 to +5 and 0 to +5v standard for newer analog stuff and their accompanying warning notices.