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Posted to alt.engineering.electrical,sci.electronics.design,sci.electronics.repair,rec.audio.tech
John Fields John Fields is offline
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Default Mixing 4 audio channels to 3?

On Sat, 12 Nov 2011 14:05:28 -0800, DaveC wrote:

Here's the latest:
...
JF


Almost! :-)

I need some absolute attenuation for the sub's output and some relative to
the input signal.

In other words: I need to be able to change the input level to the mixer
(each of the 2 sound card's level will remain most of the time at max) so I
can change volume for each stereo input (from each sound card) and for the
*relative* level of the sub. The way it is now, the sub is outputting full
level (no pots in that circuit) and the L and R channels are variable.


---
Not true.

With R12 cranked down to minimum R the output of U3 goes down to about
600µVPP out with 2VPP out of the sound card(s), and up to about 6VPP
with R12 at 10k so, if you use a 10k pot for R12, there's your center
channel volume control.
---

So, the input to the sub mixer circuit needs to come from the input pots'
wipers, not directly from the input. And U3 needs variable gain.


---
Easy enough; if that's what you want, then just disconnect R7, R8, R9,
and R10 from the sound card outputs and connect them to the pot
wipers.
---

The power amp (that this mixer is supplying the audio to) has a mute pin that
has a slow R-C tc on it, so we can eliminate S1-S3 and assoc. components, I
think.


---
The proof is in the pudding.

--
JF