Precision UNITY mixer in MU?

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Dave Peck
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Precision UNITY mixer in MU?

Post by Dave Peck » Fri Nov 30, 2018 5:56 pm

I'm looking at a few options for adding an analog sequencer module to my MU system and some of the options have everything that I need except they are missing a CV INPUT for summing the KYBD CV with the output of the sequencer, so there is no precise way to use the keyboard to transpose the sequencer (or to just use the keyboard to play the synth when you stop the sequencer, unless you unpatch the sequencer from all of the oscs and replace that connection with the KYBD CV connection).

To use one of these sequencers in a rig with a keyboard, I would need a separate precision unity CV mixer, for combining the KYBD CV signal and the sequencer output CV signal while retaining a precise 1V/OCT keyboard CV signal.

I've checked modulargrid but I haven't found what I'm looking for. Does anyone know of a simple, single-width mixer module that is intended for precision unity summing?

Like this one from Intellijel, but in MU instead of Euro:

https://intellijel.com/shop/eurorack/unity-mixer/

Thanks!

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Post by ranix » Fri Nov 30, 2018 6:04 pm

I use the Moon 544CP for that I think. There's a voltage summer segment where I can add 3 voltages together at unity gain and there are two buffered outputs and an inverted output. It also has a gate summer (w/2 outputs plus inverted), 2 channel attenuverter/mixer, slew limiter, and gate onset delay. I actually have two of these because they are super awesome.

Only downside is CP format.

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Post by Dave Peck » Fri Nov 30, 2018 6:08 pm

Thanks, but no CP row in my system :sadbanana:

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ranix
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Post by ranix » Fri Nov 30, 2018 6:12 pm

Hmm, in the mean time until you find something you could use a Q108 VCA and turn the gain up to maximum. Signal inputs 1 and 2 are unity gain added.

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Post by Dave Peck » Fri Nov 30, 2018 6:23 pm

ranix wrote:Hmm, in the mean time until you find something you could use a Q108 VCA and turn the gain up to maximum. Signal inputs 1 and 2 are unity gain added.
Tried that but it's not precise enough. All five of my Q108 VCAs and both of my MOTM-190 dual VCAs provide slightly different output levels. Not noticeable at all for audio signals but enough to ruin a precise 1v/Oct keyboard CV signal. Same with all of my various mixer modules. :sadbanana: For this purpose, it has to be something specifically designed for precise unity mixing of CV signals. Ideally with a trim pot for fine level calibration.

JohnLRice

Post by JohnLRice » Fri Nov 30, 2018 6:48 pm

The STG Active Multiples has two inputs on the bottom mult for precision adder uses. I haven't tried one myself.
http://www.stgsoundlabs.com/products/multiples_mu.htm

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Post by Huba-Swift » Fri Nov 30, 2018 7:42 pm

Does a normal DC mixer with all knobs fully clockwise not work? I suppose the accuracy there could be slightly off depending on the tolerance of the resistors used in the Op-amp summer, but it should be fairly negligible I'd imagine. VCOs also often have two 1V/Oct inputs, so you could have the sequencer going into one, and the keyboard cv into another. Or if there's only one 1V/oct input you could to use the exponential cv input of the oscillator as a 2nd 1V/oct input instead (again with the knob fully clockwise).

Edit: Just found this related thread viewtopic.php?t=89702
It seems a normal DC mixer is not sufficient!

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Post by Squattamolie » Sat Dec 01, 2018 11:39 am

The STG Active Mult is perfect for this. I ran into issues years ago with pitch CV and I held off buying the active mult because I didn't want to spend that much on "just a mult" - but once I had it, I saw it the other way: crazy to have so much invested in a nice modular and not bother to have something like an active mult that ensures 100% performance of pitch CVs. I actually could see buying another one - they're that useful.

I've also found it helpful with triggers and gates.
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Post by Dave Peck » Sat Dec 01, 2018 7:21 pm

Thanks guys! Kind of a drag that the STG costs so much more than the Intellijel Euro module ($195 vs. $75).

Thinking... I use a Dotcom Q146 'Normalizing" module to send Kybd CV & gates to all of my oscs & EGs... Maybe I could just add a couple of extra 'CV input' jacks to that Q146 panel and wire up the Intellijel module behind the panel, to sum the existing kybd CV input signal that is typically patched into the Q146 with whatever else gets connected to the new additional input jacks (i.e. sequencer output CV signal), and then send the summed signal to the existing sets of output jacks that are already on the Q146 panel... Hmm...

JohnLRice

Post by JohnLRice » Sat Dec 01, 2018 7:38 pm

Hey Dave,

If you want to DIY something you could just dedicate one group of jacks on a mult you already have and wire in a unity mixier circuit to them? You could probably find a schematic online but you might be able to use the Synthrotek Unity Gain Mixer? It's obviously intended for +-12v operation but should be able to run at +-v15v I would think? :hmm: You can buy just the PCB+panel for $20 and then just use only the amount of parts needed for the number of inputs you want. Maybe even modify it to have some 10 turn trimmers?
http://store.synthrotek.com/MST-Unity-G ... p_516.html

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Post by Dave Peck » Sat Dec 01, 2018 8:24 pm

JohnLRice wrote:Hey Dave,

If you want to DIY something you could just dedicate one group of jacks on a mult you already have and wire in a unity mixier circuit to them? You could probably find a schematic online but you might be able to use the Synthrotek Unity Gain Mixer? It's obviously intended for +-12v operation but should be able to run at +-v15v I would think? :hmm: You can buy just the PCB+panel for $20 and then just use only the amount of parts needed for the number of inputs you want. Maybe even modify it to have some 10 turn trimmers?
http://store.synthrotek.com/MST-Unity-G ... p_516.html
A-ha! That's a much better choice for the mixer circuit and it would work well either behind a spare multiple or behind the Normalizer panel. Thanks!

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Post by Synthbuilder » Sun Dec 02, 2018 8:21 am

Is there much demand for such a mixer? If so I could knock a module up pretty quickly. Given that it would be 1MU, or 1U wide, I wonder what else could be put on there to make it useful.

Tony

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Post by Flareless » Sun Dec 02, 2018 9:33 am

I think it'd be a handy device. It would save eating up a Multimix just to sum a couple of CVs as the OP wants.

A quantizer might be a nice addition perhaps?
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Post by kindredlost » Sun Dec 02, 2018 9:44 am

Synthbuilder wrote:Is there much demand for such a mixer? If so I could knock a module up pretty quickly. Given that it would be 1MU, or 1U wide, I wonder what else could be put on there to make it useful.

Tony
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Post by JohnLRice » Sun Dec 02, 2018 9:56 am

In eurorack land the precision adders like the Doepfer and VPME T43 are quite handy.
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I was thinking it would be cool to have a cross between the two, where it would look more like the Doepfer but work more like the VPME where a lot of the jacks would be gate/CV inputs that would activate the intervals when the switch is in the center/off position? So a positive or negative voltage past a certain threshold would add or subtract an octave or a 3rd etc etc.

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Post by Dave Peck » Sun Dec 02, 2018 1:58 pm

Synthbuilder wrote:Is there much demand for such a mixer? If so I could knock a module up pretty quickly. Given that it would be 1MU, or 1U wide, I wonder what else could be put on there to make it useful.

Tony
Honestly I'm not sure there would be a significant demand for this a a stand-alone MU module. Personally, I'd rather not dedicate even one space to this function which is why I would probably mount it behind an existing panel.

There wouldn't be hardly any demand at all if companies that built sequencers and quantizers (and other modules that often have their CV output summed with a KYBD CV signal) would just include a 'KYBD CV IN" jack on their module to sum that signal with whatever the module is doing :bang:

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Post by ranix » Sun Dec 02, 2018 5:47 pm

I would have wanted such a module but already have two of the abovementioned Moon modules.

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Post by KSS » Sun Dec 02, 2018 11:10 pm

Synthbuilder wrote:Is there much demand for such a mixer? If so I could knock a module up pretty quickly. Given that it would be 1MU, or 1U wide, I wonder what else could be put on there to make it useful. Tony
Start with a Q123 standards module. Lose the 440 and you have three jacks to use for unity mixing. Add an on-off-on switch to the octaves for plus-off-minus performance use. Already there for the semitones.

Would prefer to have a panel hole to the unity trim pot. Could be tightened up a bit over what Roger's done, but it needs to be big knob and performance oriented.

This would be great on its own, but if a third variable pot could be added similar in function to the Oct and Semi, even better.

Only thing left for perfection would be a jack with continuous stream of Takla Makan music. 8-)

<edit>Three knobs. Octave, Semitone, Variable.
Three on-off-on toggle switches for add plus, off, add minus whatever is selected at the switch.
Three sets of jacks, in and out for each knob. Then normal them downward. With nothing but the last output patched all the knob-switch pairs contribute.
Patch higher outputs to use knob switch separately.
Do the same on the input side. Possibly add a few PCB jumpers to personalize the preferred normalling pathways.

Deluxe version has nine jacks. In1, In2, Out. times three. Possibly bottom row has In, (normalled) Out -as above, and the rightmost bottom is always sum of all knob-switch pairs. /edit
Last edited by KSS on Sun Dec 02, 2018 11:34 pm, edited 1 time in total.

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Post by KSS » Sun Dec 02, 2018 11:14 pm

Rivera's chromatic mod for the minimoog is a similar thing.

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Post by KSS » Sun Dec 02, 2018 11:17 pm

Dave Peck wrote:There wouldn't be hardly any demand at all if companies that built sequencers and quantizers (and other modules that often have their CV output summed with a KYBD CV signal) would just include a 'KYBD CV IN" jack on their module to sum that signal with whatever the module is doing :bang:
That may be the path to choose. Simply add an input yourself DIY and if necessary a trim for op amp to dial exact unity. One jack, one resistor, one trim. Have a bourbon, scotch and beer when done to celebrate.

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Re: Precision UNITY mixer in MU?

Post by Chrutil » Mon Dec 03, 2018 2:38 am

Dave Peck wrote: To use one of these sequencers in a rig with a keyboard, I would need a separate precision unity CV mixer, for combining the KYBD CV signal and the sequencer output CV signal while retaining a precise 1V/OCT keyboard CV signal.
Hi Dave,
A few sequencers can also transpose via MIDI so you may not have to got the CV route when transposing.

Christer

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Post by steffengrondahl » Mon Dec 03, 2018 3:17 am

Dave Peck wrote:There wouldn't be hardly any demand at all if companies that built sequencers and quantizers (and other modules that often have their CV output summed with a KYBD CV signal) would just include a 'KYBD CV IN" jack on their module to sum that signal with whatever the module is doing :bang:
The Moon Modular 569 sequencer has a transpose in.
The dotcom Q119 has an add input, but only for 24 step mode.
The dotcom Q172 quantizer aid has transpose in.
Some oscillators (dotcom Q196, Corsynth C104) has several 1 V/oct inputs which (I believe) are summed.

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Post by Synthbuilder » Mon Dec 03, 2018 4:38 am

Some interesting ideas for a new module. Thanks guys. It'll give me something to think about over the holiday period.

I think a quantiser deserves its own module. I've been wanting to do one of those for ages and will look into making one next year.

Tony

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Post by Rex Coil 7 » Mon Dec 03, 2018 5:59 am

KSS wrote:
Dave Peck wrote:There wouldn't be hardly any demand at all if companies that built sequencers and quantizers (and other modules that often have their CV output summed with a KYBD CV signal) would just include a 'KYBD CV IN" jack on their module to sum that signal with whatever the module is doing :bang:
That may be the path to choose. Simply add an input yourself DIY and if necessary a trim for op amp to dial exact unity. One jack, one resistor, one trim. Have a bourbon, scotch and beer when done to celebrate.
George Thorogood would approve ... :guinness:
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Post by Rex Coil 7 » Mon Dec 03, 2018 6:06 am

JohnLRice wrote:In eurorack land the ... VPME T43s are quite handy.
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I just bought a T43 from Vladimir not but two days ago. I bought it partially assembled (toggle switches and jacks not installed on the panel) so I may make my own panel out of aluminum rather than the fiberglass material they're made with. I will also be able to place the toggles/jacks where I wish, as well as perform a few other tasks.

Nice fella, that Vladimir. :hail:
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