3U 8HP 4 Channel Panning Mixer

July 14, 2019 at 7:01 pm (maker, music) (, , , )

As I mentioned in my last post, I used an off-the-shelf 4 channel mixer board in my synth-in-a-box, but I wanted it to be accessible as a eurorack modular panel.  I also wanted it to take mono inputs and be able to set the panning as required to the L or R channels of the mixer.  I managed to squeeze it into one of my 3U, 8HP panels.

Now I didn’t need an on/off switch, and I wanted some space to add a stereo output jack, so I removed the switch and soldered a couple of links in its place as can be seen in the bottom left of this photo.  The plan was to pass the pots through the panel and use leads to connect sockets to the inputs and output.

2019-07-09 19.17.12

The panning circuit was quite simple.  I found it in the book “Make: Analog Synthesizers” by Ray Wilson from MFOS.  In chapter 7 he describes a simple circuit to allow you to hook up your (mono) sound output to a (stereo) PC sound card. It involves a 10k pot and four 2k resistors, with the wiper of the pot connected to ground.  Full details can be found in the book.

For me, I was planning to just solder the resistors directly onto the pots and sockets and then use a short stereo cable to connect to the input sockets of the mixer.  This is all shown in the following photos (complete with my dodgy machining skills).

The four input sockets are mono of course, with the stereo input signal coming off the resistor network.  The output socket is stereo. I soldered the four resistors for each channel together first then “applied” them to the pot and socket.

Then it was just a case of adding the mixer itself and making a simple power cable from the 16-pin eurorack connector to the DC barrel jack.

I used the four knobs that came with the mixer as the pan-pot knobs, as they were nice and small.  Then I used some generic ebay knobs for the volume controls.

When it came to fixing into the rack, I ended up soldering on an additional stereo lead to the output so it can be routed internally straight to the amp.  So in normal use, the output socket isn’t needed, but I can power off the amp and use the output if I wanted to send the audio off to an external amp.

I’m really pleased with how it came out. Not bad for a $15 board and a handful of components.

Kevin

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1 Comment

  1. Modular Synth in a Box | Kevin's Blog said,

    […] a panel and added some simple panning “front ends” to each input, but I’ll leave details of how I did that for another time.  For now, here is the basic case with built-in stereo speakers and […]

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