Mixing 4 audio channels to 3?

Enough to suggest a nice circuit? ;-)

Thanks, Dave

I'm learnin'! Thanks for the explanation. I'll use standard aluminum 'lytics here, connected as noted.

Dave C.

Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's confusing and someone along the line might get hurt. Grounds should be.

Yeah, I wasn't sure about that. How should I have indicated 2 separate grounds?

Thanks.

Distortion performance might be better if you run the amps in inverting mode. If you run the audio into the non-inverting inputs, the inverting input follows and the amp has to operate throughout it's common-mode range. If you use the amps in inverting mode, both the + and - inputs will stay very close to ground.

Isaac

??

What is wrong with using an op-amp to "amplify" DC? Surely they are "meant" to do that.

Isaac

I think he means that better audio results can be achieved by providing true dual-voltage supplies and eliminating all coupling caps.

The "DC amplifier" is a fine design, but will result in inferior audio performance due to the caps.

Now, if someone would volunteer such a negative voltage generator circuit... ;-)

Thanks.

It's not ground. It's Vcc/2. I generally call it Vref, or some such thing.

Exactly. Much easier than all these halved supplies, coupling caps and multiple grounds.

So, how -- exactly -- would you create that negative voltage?

Dave

Thanks John. Nice design.

What part is used for SW1-3? Purpose? If these are "anti-thump" turn-on suppression switches, I think the main amp is similarly turn-on delayed. Of course it's important to know the timing of these to avoid any window through which the sub's cone could launch (or lunch?)...

Thanks, Dave

John, what's the reason behind choosing 6.2K for the feedback R on U3 (sub op amp)? And if that is to be a pot (the original idea), is 10K appropriate?

There should be some kind of sub volume control...

Thanks, Dave

C2, C3 are polarized, so I presume electrolytic?

What type should C1 be?

Thanks.