[John Fields]

On Fri, 11 Nov 2011 09:18:16 -0800, DaveC wrote:

Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:

John, what's the reason behind choosing 6.2K for the feedback R on U3 (sub op
amp)?

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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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And if that is to be a pot (the original idea), is 10K appropriate?

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Yes, if all the other resistors are 10k.
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There should be some kind of sub volume control...

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That'll work.

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JF