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In Reply to: RE: No it doesn't posted by Tre' on April 17, 2025 at 09:48:01
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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.
"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!
Tre'
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Edits: 04/18/25 04/18/25 04/18/25 04/18/25 04/18/25
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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"
-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.
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
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Have Fun and Enjoy the Music
"Still Working the Problem"
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