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RE: This is a shunt-style balanced control.

76.90.100.230

Tre'

In Reply to: RE: This is a shunt-style balanced control. posted by Ralph on April 09, 2025 at 08:18:33

The way I see it, without the grounded center tap one channel would get louder while to other gets quieter.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Follow Ups:

Do you mean the wiper? - Ralph 10:02:43 04/16/25 (12)
Note the 220K resistor in each channel.

They are part of the shunt style balance control. No center tap is needed if the wiper is grounded; all it does is keeping the gain balanced and not mixing with the other channel if the wiper were to fail.
- RE: Do you mean the wiper? - Tre' 17:07:35 04/16/25 (11)
  No. I don't mean the wiper. I mean a grounded center tap and a grounded wiper.
  
  A 1meg pot without the grounded center will work but it will work differently.
  With a grounded center tap we have a voltage divider consisting of a 220k resistor as the series element and a 500k resistor as the shunt element. One voltage divider for each channel.
  When we turn the balance control we change the value of the shunt resistor for one channel, making it smaller, while keeping the series resistor unchanged. The shunt resistor for the other channel remains the unchanged.
  
  The volume of one channel goes down while the volume of the other channel stays the same.
  
  If there was no grounded center tap, both voltage dividers are changed when we turn the balance knob. One shunt resistor gets smaller while the other shunt resistor gets larger.
  
  The volume of one channel goes up while the volume of the other channel goes down.
  That would be the difference between a balance pot with a grounded center tap and one without.
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  
  Edits: 04/16/25 04/16/25 04/17/25
  - FWIW if you just have a grounded wiper it works exactly the same. - Ralph 08:15:36 04/17/25 (10)
    We use a shunt style balanced control in our UV-1 preamp.
    - No it doesn't - Tre' 09:48:01 04/17/25 (9)
      Without the grounded center tap the shunt resistor in one channel goes up in value as the shunt resistor value in the other channel goes down in value.
      With a grounded center tap the shunt resistor value in one channel stays the same as the shunt resistor value in the other channel goes down in value.
      How can you say that "it works exactly the same"?
      They would both be balance controls and they would both work (and maybe that is all you meant) but they are not working the same way.
      Sorry for the poor drawing.
      Tre'
      Have Fun and Enjoy the Music
      "Still Working the Problem"
      
      Edits: 04/17/25 04/17/25 04/17/25 04/17/25 04/17/25
      - Recommend you try it :) nt - Ralph 14:00:30 04/17/25 (8)
        
        In Reply to: RE: No it doesn't posted by Tre' on April 17, 2025 at 09:48:01
        
        -
        
        I don't use a balance control but I can see that it would work. Just differently. - Tre' 14:04:18 04/17/25 (7)
        
        In Reply to: RE: Recommend you try it :) nt posted by Ralph on April 17, 2025 at 14:00:30
        
        .
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        Without the grounded tap - Ralph 14:15:05 04/17/25 (6)
        
        In Reply to: RE: I don't use a balance control but I can see that it would work. Just differently. posted by Tre' on April 17, 2025 at 14:04:18
        
        The level of the channel that is not being turned down does not change.
        
        I've measured it many times since a similar circuit is in our UV-1 (single-ended) preamp. At least this is true if you set up the ratio correctly.
        
        RE: Without the grounded tap - Tre' 18:46:37 04/17/25 (5)
        
        In Reply to: RE: Without the grounded tap posted by Ralph on April 17, 2025 at 14:15:05
        
        "The level of the channel that is not being turned down does not change."
        That's some pretty good magic!
        A voltage divider with 250k as the series resistor and 500k as the shunt resistor will have 2/3 of the input voltage at the output. A voltage divider with 250k as the series resistor and 750k as the shunt resistor will have 3/4 of the input voltage at the output.
        If the voltage at the output of the voltage divider is not changing as you change the shunt resistor value from 500k to 750k, then the voltage at the input of the voltage divider must somehow be changing.
        Or it's just magic!
        
        View YouTube Video
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        Edits: 04/18/25 04/18/25 04/18/25 04/18/25 04/18/25
        
        Again, you should try it. nt - Ralph 11:56:06 04/18/25 (4)
        
        In Reply to: RE: Without the grounded tap posted by Tre' on April 17, 2025 at 18:46:37
        
        -
        
        OK. I did. - Tre' 13:25:34 04/18/25 (2)
        
        In Reply to: RE: Again, you should try it. nt posted by Ralph on April 18, 2025 at 11:56:06
        
        Here the set up. With C connected to A we have a 220k series resistor and a 470k shunt resistor. With 3 volts input there is 2 volts output. With C connected to B we have a 220k series resistor and a 690k shunt resistor. With 3 volts input there is 2.3 volts output.
        
        Tre
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        You didn't include the load of the input of the next stage - Ralph 14:27:58 04/18/25 (1)
        
        In Reply to: RE: OK. I did. posted by Tre' on April 18, 2025 at 13:25:34
        
        -which affects that reading although not by much.
        
        You'd need a bigger change before that sort of thing would be noticeable. As long as the values are chosen conservatively its no worries. We've used lower values in our stuff based on the idea of greater Johnson noise in higher value resistors (the series part). We use 49.9K and a 1M shunt.
        
        There isn't one. - Tre' 15:49:31 04/18/25 (0)
        
        In Reply to: RE: You didn't include the load of the input of the next stage posted by Ralph on April 18, 2025 at 14:27:58
        
        The shunt resistor is the grid resistor for the next stage so there is no
        "load of the input of the next stage".
        And even if there was, that would not change anything. The load would be in parallel with the value of the shunt resistor of the voltage divider and if the shunt resistor value resistor changes value, the amount of attenuation of the voltage divider would change. Just not as directly as in this case, but change it would. You can take that to the bank.
        Ralph, you went from saying "it works exactly the same" and "The level of the channel that is not being turned down does not change" to "before that sort of thing would be noticeable". Either something is different or it's not. Whether or not it's noticeable has nothing to do with what I am (and have been) saying.
        Using a pot with a grounded center tap vs. using a pot without a grounded center tap as part of a balance control...the two will not operate the same. Not in a technical sense. And noticeable or not, the voltage will change when the shunt resistance changes. And by saying "before that sort of thing would be noticeable" you admitted it.
        You could have just started there and then proceeded to explain to me why that won't matter in practice.
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        Edits: 04/18/25 04/18/25 04/18/25 04/18/25 04/18/25
        
        OK. I will. nt - Tre' 12:51:17 04/18/25 (0)
        
        In Reply to: RE: Again, you should try it. nt posted by Ralph on April 18, 2025 at 11:56:06
        
        .
        Have Fun and Enjoy the Music
        "Still Working the Problem"

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