Mixing 4 audio channels to 3?



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Of course, but if an AC input and output is desired and no negative
supply is available, the input and output must be capacitively
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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.
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On Wed, 09 Nov 2011 20:32:36 GMT, snipped-for-privacy@spam.com (Don Pearce) wrote:

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Amen to that!

The beauty parts are that it doesn't need to be regulated, it only
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Enough to suggest a nice circuit? ;-)
Thanks, Dave
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Sure, a 555 charge pump.

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Suggest a circuit...?
Thanks.
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KISS
--
Stuart Winsor

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On Wed, 09 Nov 2011 20:49:28 +0000 (GMT), Stuart

Exactly. Much easier than all these halved supplies, coupling caps and multiple grounds.
d
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So, how -- exactly -- would you create that negative voltage?
Dave
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Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:
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"mF" means microfarad?
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No, "mF" means millifarad, = 1000F

Here's the latest:
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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.
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.
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.
Thanks!
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Not true.

With R12 cranked down to minimum R the output of U3 goes down to about
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Yeah, R12 needs to be a pot. That does it.
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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
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A 4066 would work well.
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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
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It makes the output of the sub channel approximately equal to the
outputs of the other channels with 1VPP inputs from the four sources.
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C2, C3 are polarized, so I presume electrolytic?
What type should C1 be?
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