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Building a sound mixer within my guitar amp with line IN & mic input

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dazz:
I think I already asked this, but can I reference the opamp to Vref like this and get rid of C13? or will that ruin my opamp's CMRR?
It seems to allow for a much lower supply voltage without distorting. I simmed it at 12V, but works at 9V too

EDIT: I forgot to swap the tl082 for a NC5532 there, but still seems to do the trick

Yansi:
Balance pins are common on single-per-package opamps. These are used to trim the offset voltage to zero (you are balancing the input stage within the opamp).  For an audio signal application, this is of a not that much of an issue, as a small output offset voltage is stripped by the coupling capacitors. (But it may be an issue in DC coupled circuits, such as power amplifiers).

The comp pin is not very often seen now, but it serves to connecting an external compensation capacitor to change behavior ("slow down") the opamp a bit, to make feedback loops stable.

Yansi:

--- Quote from: dazz on June 06, 2019, 10:09:58 pm ---I think I already asked this, but can I reference the opamp to Vref like this and get rid of C13? or will that ruin my opamp's CMRR?
It seems to allow for a much lower supply voltage without distorting. I simmed it at 12V, but works at 9V too

--- End quote ---

Good question! Not sure of hand, as I usually design these circuits with a symetrical supply voltage, but thinking about it...

If your VREF source is low impedance and well bypassed against ground (which it should be!), then connect it against VREF.

How is your VREF source circuit implemented?

dazz:

--- Quote from: Yansi on June 06, 2019, 10:17:57 pm ---
--- Quote from: dazz on June 06, 2019, 10:09:58 pm ---I think I already asked this, but can I reference the opamp to Vref like this and get rid of C13? or will that ruin my opamp's CMRR?
It seems to allow for a much lower supply voltage without distorting. I simmed it at 12V, but works at 9V too

--- End quote ---

Good question! Not sure of hand, as I usually design these circuits with a symetrical supply voltage, but thinking about it...

If your VREF source is low impedance and well bypassed against ground (which it should be!), then connect it against VREF.

How is your VREF source circuit implemented?

--- End quote ---

It's a simple voltage divider with 1k resistors (had to lower them as the load seemed too much for higher resistor values and Vref dropped significantly)
But if I use NC5532's instead, since they're dual opamps, I can use one half to buffer the resistor divider and get very low impedance, right?

dazz:
See green box for Vref circuit as it stands for now. Measured some 150mW across the 1K resistors at 24V Vdd

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