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 !
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
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.
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.
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
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)
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…
Hello,
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.
