Super Simple Mixer

Hello. I’m building a unique mixer for a project, that requires an input signal to be split into 4 signals, which then go on to go through potentiometers

The super simple mixer has 3 in, and 1 out. Would it be possible to reverse this process still using that chip, so that I can have 1 in and 3 out etc??


it’s not a mixer that you need, it’s a Multiple module
(one enter who split in several out the same signal)

i just add a switch to have 1 input to 3 out put (all x2)
or 1 input to 6 output

and yes you can use TL072 or TL074 for build a Buffered Multiple :slight_smile:


You can deffo do this! If you look at a buffered multiple circuit like this:

then just replace the 1K resistor on the outputs with a pot (I guess anything really? preferably log tapered for audio?) you’ll have what you’re after, I think.


Thanks so much man! Really appreciate it!!

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Why do you think you need anything other than your potentiometers?

It depends on the source of your signal how you need to approach this.
If your source has a low output resistance you can easily connect all potentiometers in parallel and you can take the individual signals from each potentiometer. No need for any additional circuitry.

What is your signal source?


I’m somewhat embarrassed to say I’m having issues with the super simple mixer (two of)

I don’t get an output and when I plug my oscillators in they seem to freeze (the fine tune knob doesn’t change the frequency according to the tuner display). I’m worried this might be damaging the oscillators

Using a signal generator I noticed a weird DC shift downwards when I plugged the signal generator into one of the mixer channels. Scoping the op amp pins I found an inverted output at the first op amp output pin but nothing at the second

The input chip voltages are correct

I replaced the op amps and was getting an output on the scope that looked like the input when fed by the signal generator, but still no audio out although one of the two works as a passive summer when not plugged in.

Any suggestions from this evidence? Otherwise I’ll just have to pull it apart a bit and have another go at walking along the schematic

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I think your Molex connectors are wired backwards. Here’s Sam’s:

Looks like his grounds are the blue wires and they go to the lower pin (closest to the IC).



Appears ground is yellow, and is going to the upper pin (away from the IC).

If both modules are having similar problems that makes it unlikely there’s an assembly problem like a bad joint or solder bridge. That kind of leaves something systematic such as bad op amp, wrong resistor values (I can’t make out the color bands in your photo), backwards wiring on the Molex, or bad power supply.

The oscillator behavior is troublesome. The mixer inputs are supposed to connect to 100k pots with 100k resistors in series on the wipers. If those values are indeed what you used it’s hard to see what could mess with the oscillator… but if the Molex wiring is backwards (meaning the VCO output is being shorted to ground) that would maybe explain at least some of this. Shouldn’t damage the VCO though. Hmm, I’d forgotten the 1222 has no current limiting resistors on its outputs. So it’d be shorting the buffer op amps to ground. But the TL07x can withstand a short to ground indefinitely. And the Nano is connected to the ramp output after the buffer… fortunately it does have a series 1k resistor, so that’s protected. Just to check, does the tuner display go unresponsive if you plug the triangle or square output into the mixer, or just the ramp? I can’t see any way it’d mess up the ramp output going to the tuner if you’re using the triangle or square output.

Anyway, that sounds like something whacko at the input. Check the Molex, and if that’s not it, check the input resistance. If you unplug the cable at the VCO and measure the resistance from cable tip (on the cable) to ground (on the module, not the cable) it should be 50–100k (with the channel switch on, with it off it should be infinite).


Thank you so much for such a detailed assessment! I’ve run out of time today but I’ll go through thoroughly point by point tomorrow

I didn’t double check which way around the molex should be so it’s entirely possible they are backwards.

I feel like my trouble shooting skills have improved massively so I wasn’t expecting to be stumped by this module!

I really appreciate your time


How would you normally go about determining correct orientation for things like this? I guess following the sleeve contact and checking it is connecting to ground?

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Just read through this in more detail and it makes a lot of sense. It was the ramp I was using for testing.

Would you normally add resistance to your outputs in case of them being shorted further down the line?


Very much more often than not there will be a 1k resistor in series with the output. It’s a little surprising when there isn’t one. As I understand it this is to some extent a holdover from very early op amp days when they could not tolerate a short to ground or a power rail; as mentioned above, the slightly less ancient TL07x can be shorted indefinitely without damage. But it’ll use a lot of current doing so which could cause other problems; also, if you accidentally plug one such output into another such output, the two op amps will behave bizarrely as both try to set the same point to two different voltages. With series resistors the op amps will both be happy and indeed people with banana jack systems have been known to deliberately stack outputs together as a ghetto passive mixer.


Thank you, it’s only recently I’ve started thinking about what happens when circuits actually interact with one another. It interesting and occasionally surprising!


JLCPCB will soon be getting a new order from me for exactly that reason!


I guess we never stop learning :slightly_smiling_face:

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