Passive Balance Control?
Jun 2, 2014 at 3:41 PM Thread Starter Post #1 of 4

SteveSound

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I need a universal pseudo-balance control to move between stacks.  I say pseudo, because I don't need a full/classical sort of balance control.  Just an adjustment on one side.
 
Reason: I have hearing loss on the left side that varies from 3 to 10 db, depending on volume levels.  I'd like to simply turn down the right side as needed.  Using software plugins works in some situations, but not on everything I like to do.
 
Ideally it would be a passive box with RCA connectors that can be used in different stacks.  Here's what I'm thinking:
 
 

 
 
So I have 3 questions:
 
1. Is this a viable idea in terms of not screwing up the fidelity?
 
2. What value should the POT be?  I want about 0 to ~12db of attenuation.
 
3. Should I add R1 as if it were a normal balance control?  In other words, if the POT is 50k, should I have a 50k resistor for the left channel to keep things even?
 
Jun 3, 2014 at 2:33 PM Post #2 of 4
Hope this link helps:
 
http://www.angelfire.com/electronic/funwithtubes/Amp-Bal.html
 
Try circuit "C" with modifications necessary to get low output impedance, and desired range. 
*values as a starting point*
Omit the 120Kohm resistor between input and pot
Use a 5Kohm linear pot
10Kohm resistor from pot to ground. 
*values as a starting point*
 
Please let me know if my guessed values work. They could be totally off, I did not even use a cocktail napkin to estimate...
 
Jun 4, 2014 at 12:56 AM Post #3 of 4
  Hope this link helps:
 
http://www.angelfire.com/electronic/funwithtubes/Amp-Bal.html
 
Try circuit "C" with modifications necessary to get low output impedance, and desired range. 
*values as a starting point*
Omit the 120Kohm resistor between input and pot
Use a 5Kohm linear pot
10Kohm resistor from pot to ground. 
*values as a starting point*
 
Please let me know if my guessed values work. They could be totally off, I did not even use a cocktail napkin to estimate...

 
Thanks for the starting values nikongod!  I'll pick up the parts and give it a go.
 
Jun 4, 2014 at 7:09 PM Post #4 of 4

 
I found the calculations for DB drop (easier than I thought). Given R1 = 5k and R2 = 10K, there is only a 3db drop without load. However, with load it all changes and I really don't know what that might be.
 
Before I hook up the Minimax with fixed resistors as a test, I'd like to double check.  Is R1=25k and R2=10K a safe combo?  Or would 100/47 be better?
 

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