DIY Passive Mixer Problem

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randytomlinson67

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Apr 10, 2022
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Hi all. Im building a passive 3 Chanel Mixer and when i send a Signal to CH1 Potentiometer for CH1 works fine but if i close Pot CH2 and/or CH3 the Signal of CH1 closes to!!??
How can i prevent this? Pot 2 & 3 should not Affect the Signal on CH1
I have added a Master Pot at the end of the 3 1k Res before going into the Output. thank you
Randy
passive-audio-mixer-schematic.png
 
The 1K summing resistors need to be greater than the value of the pot (10K). Try 47K.

Please post a link to the website.

Cheers

Ian
 
Hi all. Im building a passive 3 Chanel Mixer and when i send a Signal to CH1 Potentiometer for CH1 works fine but if i close Pot CH2 and/or CH3 the Signal of CH1 closes to!!??
How can i prevent this? Pot 2 & 3 should not Affect the Signal on CH1
I have added a Master Pot at the end of the 3 1k Res before going into the Output. thank you
Randy
View attachment 94235
Pots 2 and 3 should definitely affect the level of the signal on channel one with the schematic you showed, this is the pain with passive mixers, al inputs interact with each other. I'm not sure what you mean when you say that the signal "closes", do you have all three inputs connected? what do you have connected to the output? BTW I fail to see the utility of having bridged outputs, do you need this?

My suggestion, if you really want a passive mixer, ditch the potentiometers and use fixed resistors so it becomes a passive summing bus. If you want level controls, make it an active mixer and current sum so the controls don't interact with each other, there is really no free lunch.
 
Last edited:
The classic trade off in passive mixers is insertion loss... Summing N number of signal stems will attenuate each input signal roughly 1/N. The typical make up gain stage to restore signal level is indistinguishable performance wise from active combining with virtual earth or equivalent active stages.

This too is mature technology so keep searching for better examples.

JR
 

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