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Quote from: Jbliss on June 19, 2016, 01:15:50 pmQuote from: Hero999 on June 19, 2016, 01:09:19 pmThe amount of noise depends on the type of op-amp used and the source impedance.What sort of microphones are they?I would be a line level output from a RF Mic receiver.I'd just use the circuit linked to in my previous post with 1k resistors all round and an NE5532 op-amp.
Quote from: Hero999 on June 19, 2016, 01:09:19 pmThe amount of noise depends on the type of op-amp used and the source impedance.What sort of microphones are they?I would be a line level output from a RF Mic receiver.
The amount of noise depends on the type of op-amp used and the source impedance.What sort of microphones are they?
An inverting opamp with 1k input resistors cannot use 10k volume controls because the 1k will load down the 10k control so much that it will be difficult to adjust the level. Maybe use 20k input resistors fed from 10k volume controls.
So would you Have the pot first then the fixed or other way?
Quote from: Jbliss on June 28, 2016, 01:56:13 pmSo would you Have the pot first then the fixed or other way?If the input goes to the fixed series resistor which feeds the pot to ground then when the pot is turned down the low frequency gain of the opamp will be a few hundred thousand and its output noise will be very very high. Actually the output of the opamp will be as high as it can go and it will not amplify because it will be amplifying its DC bias voltage or its input offset voltage instead.
Might want to stick a small cap on each input too to block any DC.Also perhaps a pot for each input (along with a smaller fixed resistor) to set relative levels for each source?