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Summing mixer question
Old 28th December 2018
  #1
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Mylithra's Avatar
 
๐ŸŽง 10 years
Summing mixer question

Working on a summing mixer and have a question about setting input impedance.
Is any resistor on the input side of the transformer necessary? I just want to make sure I dont need something on the input side of the transformer to properly load the output of the Converter. I'm pretty certain I have the math on the mixer parts right.
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Old 28th December 2018
  #2
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๐ŸŽง 15 years
Hi
Resistors R1, 2, 7, and 8 are not needed unless your convertor happened to have transformer outputs and demanded a specific load.
Basically, NO!
Matt S
Old 28th December 2018
  #3
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Radardoug's Avatar
 
๐ŸŽง 10 years
Your summing mixer method is very expensive with transformers on every input. Better to use one transformer on the output. And your resistor values result in very low output. Not the best way to do it.
Old 28th December 2018 | Show parent
  #4
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Mylithra's Avatar
 
๐ŸŽง 10 years
Quote:
Originally Posted by Radardoug โžก๏ธ
Your summing mixer method is very expensive with transformers on every input. Better to use one transformer on the output. And your resistor values result in very low output. Not the best way to do it.
It is.. but the idea is I am going to have different pairs of transformers on each stereo pair. I want to be able to push them into a little saturation then make up the gain after mixing. This is more of a color thing. So far, I have a Carnhill, Sowter, Jenson and a custom pair. I have another set of API style transformers but dont know that I want to expand this beyond what a single DB25 is going to hold. At that point, it make cabling it a PITA in my case.
Old 28th December 2018
  #5
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Radardoug's Avatar
 
๐ŸŽง 10 years
Well, you dont need the terminating resistors on the output, they just add loss. And the 10K's are high. Better to make a matched 600 ohm system, the resistors on each input are the loads for the other inputs. Doing it the way you are doing it, with different transformers, it could end up very messy, or maybe not.
Old 30th December 2018
  #6
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ruffrecords's Avatar
 
๐ŸŽง 10 years
If the input transformers ar 10K:10K types I would recommend changing the bus resistors to 5K1 each rather than 10K. There will be 6dB less bus loss overall and a similar improvement in noise. I would raise the 165R resistors to about 200 ohms. With the 2K5 resistance due to the paralleled bus resistors the output impedance will be less than 200 ohms which most mic pres will be happy with.

Cheers

Ian
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