Author Topic: Summing mixer  (Read 9130 times)

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Offline JblissTopic starter

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Re: Summing mixer
« Reply #25 on: June 27, 2016, 01:54:25 pm »
The 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.


So you would say 10k potentiometer then a 1k fixed
 

Offline Audioguru

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Re: Summing mixer
« Reply #26 on: June 27, 2016, 03:00:40 pm »
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.
 

Offline JblissTopic starter

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Re: Summing mixer
« Reply #27 on: June 28, 2016, 01:56:13 pm »
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.

Thanks for your input will definitely implement.   :D :D So would you Have the pot first then the fixed or other way. 
thanks
 

Offline Audioguru

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Re: Summing mixer
« Reply #28 on: June 28, 2016, 03:38:50 pm »
So 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.
 

Offline JblissTopic starter

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Re: Summing mixer
« Reply #29 on: June 29, 2016, 01:29:01 pm »
So 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.

so pot first then fixed. thats what most of the circuits I have seen implement
thanks 
 

Offline JblissTopic starter

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Re: Summing mixer
« Reply #30 on: June 30, 2016, 02:06:19 pm »
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?

so say a 10k Pot then a 20k Fixed resistor. ???


Thanks
 


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