Matrix mixers

DIY active Matrix Mixer, 8 Inputs, 5 outputs

looks like I have a problem with Instagram embedding? Link works, but no picture here
Matrixmixer 8*5
The four separate pots are not yet connected.
#matrixmixer #sdiy #synthdiy #noise #darkambientmusic #noaudienceunderground


just want to congratulate you on what looks like a great DIY Serge/CGS system! sounding great, too.

thank you very much!

How’s the audio quality of the 4ms matrix mixer? I’ve encountered mixed opinions online.


I don’t think I have a very discerning ear so I probably wouldn’t listen to me, but I thought it sounded alright. I ended up selling it cus I just couldn’t justify the cost(and realized I don’t need/know what to do with 16 vca’s :sweat_smile:)

For what it’s worth, mine sounds amazing and will soon be joined by a second.

anyone else have any experience with the doepfer

Yep, it’s great. Mine is in constant use.

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I use it mostly for audio, routing FX chains. It’s a simple modul and it works fine. I wishes sometimes to have more channels or get a secound one. Stereo would be nice to…


yeah stereo would be truly amazing

Yep, I often use it for CV mixing, nice touch are the uni/bipolar switches, I sometimes flip them as a quick way to get “something else”, more often than not the results are rather useful. :wink:


Do you or @Jonny have any pointers for DIYing, like schematics, op amp choices, etc?

I’d like to find a 4x4 (or 6x4) stereo* matrix mixer, and suspect it’s a unique enough thing that I’ll need to DIY it.

The best resource I’ve found so far is, but I’m really confused why the pots should be linear and not log.

*”stereo” meaning, 4x4 would actually be 8x8 channels, but with 4x4 dual pots

I looked at that site and the Mickey Delph and Lowgain Electronics designs. Btw, the pot wiring diagram on that linked site is backwards if I recall correctly.

They all use linear pots, so I went with that, but I’m not sure exactly why that’s the standard case. These passive designs are somewhat primitive and can be noisy or prone to impedance mismatches, so that might have something to do with it. I guess one benefit would be mixing CV signals if you wanted to.

I would not want to build a stereo (passive) version. The larger your passive matrix, the noisier and more lossy it’s going to be and you’d also need to have higher levels to drive it. Personally, if I were doing it again, I’d buy the Low Gain PCB or design one similar to avoid all the wiring which is a real pain.


That’s the standard design, you can expand it to as many potentiometers as you want.
You can take any standard-opamp you want, TL074 for example. That’s ok for audio frequencies. There are also types with less noise, NE5532 for example. But I don’t think noise is a problem here. Anyway, even the better ones cost less than 1€
These are the standard for most synth design you’ll find in the internet.
The secret of logarithmic are the 15k resistors. They simulate a logarithmic curve. Look at the lower left corner of the schematic.


Per forum rules, the group buy discussion has been moved to the Potential Group Buys thread in Trade. If anyone else in the EU is interested in this 6x6 stereo mixer idea, please join the discussion over here :slight_smile:


One question regarding Matrix Mixers … Has anyone tried out the Doepfer A-138M? I would like to buy it, but first there’s one thing I would like to know about it … Let me explain …

I have right now the SSR Labs Matrix mixer, which uses the Sinthy style of pins to route the signal. But there’s one problem that I don’t know if it’s shared by all types of matrix mixers or not. To simplify things let’s say that:

  • I have 4 inputs (1, 2, 3 and 4) and 4 outputs (A, B, C and D).

  • I connect 1 with A, I get input 1 in output A … Correct!

  • I also connect 2 with A, so I get 1+2 in output A. Correct! But …

  • If I connect the 1 with D, I get 1+2 in output D, as they are linked in last step so the share some connection.

Is that normal? Is something to expect in all matrix mixers, or do the have some king of system to avoid the signal to go backwards?

And one more thing … In the SSR LAbs inputs and outputs are labeled as this, but you can actually plug inputs in the outputs as the routing seems to just connect them. By doing so, as they are connected, I get some strange behaviour in the Teletype lights as some voltages are going backwards inside the inputs jacks … I don’t know if it’s clear enough … Sorry for my english …

I love my A-138m! And it does not behave the way you’re describing…

(edit: more knowledgeable response below :slight_smile: A-138m is an active mixer!)

The SSR uses a switch array IC and I can’t say without seeing the pcb or a schematic but I’m guessing given its depth/construction, thats it - no additional op amps or anything in the signal flow. According to their site “This matrix has onboard 16 bi-directional “Row” IOs enumerated with digits, and 8 bi-directional “Columns” IOs enumerated with letters.” This is basically a way of saying its a passive matrix. Any passive matrix will behave in this way, however active ones will not.

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Yes, I think I’m going for the A-138M … The bidirectional behaviour of the SSR LABS is something I did not expect. When I saw the lights of the trigger in the Teletype blinking when there was a connection between inputs and outputs I started to worry about this. And when you use it with audio signals the leds creates some kind of high pitched noise in the output, so right now is a pretty useless module. I should had taken more time reading about this module before buying it.

Anyway, let’s go for the A-138M. I want to use it with audio feedbacks but also with CV’s …

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One nice thing about the 138m is that the pots can be polarizers and one row can be offsets. Very useful features that some other matrix mixers lack. Combine it with a switch and it’s pretty easy to make a sequencer out of it.