1163 Mini Mixer

Hey, is the fartbox still working when the mixer is plugged on the same power supply ?
It could be that you do not get the +/12V supplied properly. I have this problem sometimes. Only the neg rail is being supplied. The sound you can hear could be just “passive” (no amplification). When you unplug, the power might send a short +12V to the opamp and give you a second of signal

My view is that the capacitors are not absolutely needed to get this mixer to work. It is much better with it but it would work without it.

If you can, check the opamp has got the +12-12V supplied on the correct pin (4 and 8) and you can also check continuity, this circuit is tiny so it shouldn’t take too long.
Good luck !

you cant go far wrong with it, have you checked the poer rails at the opamp?

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I think the mixer is (mostly) fine. I killed the fbox i used as power supply. if you like drama you can follow my progress in the fbox thread. to keep it short and on topic: i’ll report back when i have my basics sorted :wink:

thx for your support and encouragement


Not too sure what you mean by using the FB as a power supply

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Do you mean you’re taking the +/- 12V/ground connections from the fartbox? How is that being supplied?

By “any resistor”, I think the BOM means the type of resistor (metal film, carbon film, wirewound, etc), not the value (measured in ohms - 500k, 100r, 2M, etc). Have you used the values from the ‘Designation’ column?

Totally OT side note: would it work to have a seperate category for all the ‘official’ module topics? I often find myself having to search for them, and they aren’t all titled the same way which means it becomes quite cumbersome to find them after a while.

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Does this help?

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I don’t know how I forgot about that. It only appears pinned when I log out, but that might just be my profile settings. Thanks! Bookmarked for future reference.

  • @Bpbby was right. pin 8 was missing it’s 12v
  • circumvented any power proplems i might have had by adding a “paid & prebuilt” power supply
  • now it’s working (demo clip)

Having similar problems, no sound coming out.

Pin 8 seems to be connected to ground, c3 and +12v don’t seem to be connected to pin 8 or ground. Not sure how this is happening

  • using b100k pots
  • using on/off switches with no third pin
  • is the power connector at the bottom? input 1 is at the top on the front panel but input 1 is at the bottom near the output on the back. I plugged 1 into 6, 2 into 5 etc. and output into output
  • checked plugging in input one and adjusting input 6

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is the TLO72 and power header oriented correctly. There’s nothing else that can really go wrong, but if your not getting the correct voltages at the OP AMP nothing is going to work,

Yup the notch’s is pointing away from the power socket.

I removed the chip and header to see if pin 8 still connects to ground and it does

Looking closely, surely I’m seeing this wrong but pin 8 shouldn’t connect to pin 3 over the large area right? (pin 3 should connect to ground though, which it does)

You appear to have drawn a line between pins 3 and 5, not 3 and 8.



OMG thanks so much, i knew i must have been thinking about it wrong somehow but i couldn’t see it

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Just want to confirm two things

  1. is it ok to use two pin switches leaving the third pin on the board empty?
  2. having input 1 on the face plate connect to 6, 2 to 5 etc.?

It is OK… IF you have put them in in the right orientation…
Unfortunately I don’t own that module so I can’t confirm if your orientation is the correct one.
Try shorting with a wire the middle pin and the non-connected pad of one switch and see if it works…


Two pin switches are fine and your orientation is correct.

The inputs are all identical except in name, so having the legends reversed between PCB/FP has no effect.

Are you getting +12 and -12V on the correct pins on the OP-AMP.

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I was breadboarding this module from the schematic and I have an issue. Every time i add an input volume it adds to the output voltage and so it outputs 5v with a single input, 10v with 2 inputs …
What i’m doing wrong?

Sounds like nothing wrong, if I understand your question. A mixer adds its inputs. Of course you can’t get much more than 10 V out of the op amp, so with a third input, if all of them are 5 V, the output will be clipped. Assuming you don’t want clipping, you then have to back down on the three (or four, five, or six) attenuator pots. I like mixers that have a variable resistor in the first stage feedback for that reason, you can just decrease the gain on that stage instead of having to fiddle with all the input pots.


The problem is when i add the 3rd input it goes 15v , and up to 20v with the 4th one. Is it intended to do so??? What can I check, maybe I did something wrong on the inverting Opamp?

That’s kind of impossible, unless something is really wrong. How are you measuring the voltage? Between which two points? The op amp has, or should have, ±12 V power, so if you measure from TL072 pin 7 to ground it has to be less than that, maximum about ±10.5 V. Same from pin 1 to ground. Pin 4 to ground should be -12 V and pin 8 to ground should be +12 V.

What are you putting into the inputs?

Check also your multimeter settings, make sure it’s DC voltage, in an appropriate range.

Post a picture of your breadboard.