Todays project is a very, very simple 4 channel mixer. For an active mixer, I don’t think it could be any simpler. And for a simple mixer, it’s got quite a few nice features. These extra features of it are: individual gain adjustment, master gain adjustment, mute switches for individual channels, and LEDs for signal indication… Very helpful for when there’s an annoying buzz coming somewhere from your synth but you just can’t find it!
In this stripboard layout, there are a couple of mods you can do to improve its performance. The first is to add 2 x 100nF capacitors on the power supply. One for +12v to ground, and the other from -12v to ground. Make sure these are not polarized! Fitting these will significantly improve the noise emitted by the power supply and ICs. You’ll see them in pretty much all eurorack synthesizer designs, and as they don’t cost much, it’s worth fitting them anyway! I haven’t included them in the stripboard layout, purely for simplicity for beginner synth DIY builders.
Another mod that you could do for this circuit is to add as more inputs. You can add as many channels as you’d like! All you need to do, is copy the input section from what is already there, and just add it again to pin 2 of IC1. So you’ll just need a pot, switch and 100k resistor in parallel with pin 2 on IC1… Can’t really get much simpler than that. Look at the schematics at the bottom of the page to make more sense of what I mean.
For now, here is the tried & tested stripboard layout for the circuit:
It looks more difficult than it actually is, just make sure you read the notes for it and it should be easy enough to follow.
If you’re interested in adding more inputs to the mixer, or you’re interested in how it works, here are the schematics…
This is also the first ever project that I had PCBs made for to try to give a little more professional look to my synth.