Electronics > Beginners
Just how bad is it? Audio mixer with headphone amp.
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Audioguru:
This simple mixer has only 3 inputs, not 24.
BrianHG:
I think that paulca's design, though not necessarily some of our chosen topology/techniques for a 3 channel line level mixer, with some of the changes already made above, like the volume at the RCA inputs & most of everything else remaining the same will function excellently for his intended use.  The ne5532, even with some gain, will have such a quiet noise floor that he wont hear a thing so long as the PCB is well laid out.

As for the power supply, with an AC out wallwart.  Just use power wire A direct to GND, then the other goes through the optional resistor in series, to the 2 diodes (both tied at that point, just 1 forward, 1 backward).  Add your power filter caps there, I like something like 10000uf 25v each, or higher. (This is already overkill, but I like my audio filter caps huge and you are doing half phase rectification if you power supply is done like this...)  For a 12v AC adapter, you should get around +16v on the forward diode and -16v on the reverse diode.  Put those 2 voltages through your 7812 and 7912 and you will have a clean +/- 12v.
paulca:
Thanks.  I don't have a negative regulator to hand :(

As per my other thread I have two of my bench supplies in series, but I'm too scared to lift them above 1V.  I don't what they to go bang.

One is powered off a battery, the other off a LED Lighting DC supply.
paulca:
On the amp design.  I am waiting bread boarding a few things before getting back into the design.

I hope to start with one input amp.  Test it with a scope.  Then try a second.  Then try a mix amp.

I'm sure at that stage I will have messed something up!
BrianHG:
if you have 1w or 5w approx 12v zener diodes, you can make a second R/C filter stage at your power input caps and parallel the zeners in parallel to limit voltage to 12v on each cap.  That will suffice.
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