3 in 1 out mixer issues...

G

gwyador

New member
I bought the 3-in to 1 out mixer and have built it up but I am getting distortion and a gate like cutting out from all channels... Has anyone else experienced this? I am wondering if I can get the schematic since you have not posted the build documents on this pcb yet... Yes it is a simple circuit but I am not sure where I have gone wrong... I get sound from all inputs it is just distorted and cuts out as it fades on all channels... I thought maybe I had a bad chip and since I socketed them I swapped the output chip and no change... at any rate if you can provide me the schematic for this I can troubleshoot further... If anyone else has any odeas I am open as well... could a bad solder joint somewhere cause this? thanks! Bryan
 
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The schematics for both the Splitter and Mixer have been uploaded elsewhere on the forum, (in another thread I posted a link to them just yesterday) you'll find them if you SEARCH.

SOP for a trouble-shooting thread is to post well-lit pics of your build including front/back/all wiring.


*BTW, I've tried 3 times now to edit this post to add links to the schematics, and it's not working, but the link to the search engine posted just fine.
 
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power rails to all chips look good! not sure what would cause the gate-like effect I am hearing... very curious... I am looking for shorts on the PCB at this point but a schematic would really help!
 
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I really do not know what pictures will help with but here goes... As I said, rails look good but I swapped the tl072's out for tl972's in case the signal level was somehow reaching close to the rails and I found if I turn the volumes down about halfway with the 972's installed I can get continuous sound but if I turn it up past about halfway I lose sound... I would have thought it was an op-amp issue except for that symptom. Was this mixer designed for line signals? If so, are the caps there to gate the signal below a threshold? I'm tempted to remove them and see. does anyone have thoughts on this?
 

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Pretty sure (99.8%) this mixer is meant for instrument-level.

Danged if I know what the problem is. I was going to suggest re-seating IC #3 (3rd from left), but if you've already swapped out the ICs...

A short/partial-short under one of the IC-sockets? Perhaps the one handling the actual mixing, as you said the problem's happening on all channels.

The fading indicates it might be a problem with a cap, so peut-etre a bad cap? That could also explain the distortion, a bad cap.


I'm not a good trouble-shooter, I know, but people tell me I'm trying...
 
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gwyador said:
if I turn it up past about halfway I lose sound
Click to expand...
Normally I'd hear this symptom and think it was a volume pot with legs mixed up. But your wiring looks good from the picture, and based on the schematic all four pots are gain knobs with legs 2 and 3 connected together anyway.

You used 100 pf caps and not 100 nf for C2, C4, C6, and C7, correct? If that's not it I'm out of ideas. Maybe the next thing I'd consider would be a defective volume pot going open circuit.
 
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