Bal-Bal, gain with volume control
I posted this on the longer thread last week and I only got a reply suggesting that I switch to SE at my input to make volume control easier and then go balanced for my output. I really want this to be bal bal.
But, I am unsure if I understand this correctly:
I think gain is Rf/Ri, and from the thread note that if I want to use an attenuator, 10 K should be a good value (works fine with my source), I should up Ri and Rf to 10K. So—with a 10K pot and 10K Ri, is the input impedance 5K? does this mean that for a gain of 2, I leave Rf at 10K?
I posted this on the longer thread last week and I only got a reply suggesting that I switch to SE at my input to make volume control easier and then go balanced for my output. I really want this to be bal bal.
But, I am unsure if I understand this correctly:
I think gain is Rf/Ri, and from the thread note that if I want to use an attenuator, 10 K should be a good value (works fine with my source), I should up Ri and Rf to 10K. So—with a 10K pot and 10K Ri, is the input impedance 5K? does this mean that for a gain of 2, I leave Rf at 10K?
picovolt, you don't have to switch to SE to have a balanced volume control. If you have already googled balanced volume control, there is one method you will see that you have to put 2 resistors in series with the inputs of the op amps and then a volume control in between the inputs. You don't have to mod the boards, just add the parts externally to the board.
this is Bruno Putzeys bal vol control
4 parts on grounding each worth reading
http://www.edn.com/design/consumer/4429968/2/The-G-word--How-to-get-your-audio-off-the-ground
http://www.edn.com/design/consumer/...ow-to-get-your-audio-off-the-ground--Part-2--
http://www.edn.com/design/consumer/4430977/The-G-word--How-to-get-your-audio-off-the-ground--Part-3-
Part4 is specifically a bal to unbal with unbalanced active vol control and then back to bal for the output.
Note the the bal output is actually a "Balanced Impedance" connection. It is very similar to Jensen's in apnote3
see 2.4 a simple alternative.
http://www.edn.com/Home/PrintView?contentItemId=4431638
Bal converted to unbal to vol pot, then convert back to bal seems to be the only way to do it properly.
That's what I told you last week.
But you don't like the answer!
BTW,
there is a follow up in the "comments" pointing out that the rise in LF distortion starting @~200Hz was due to his mistakenly using a log pot in the active vol control feedback link.
He confirms this added distortion is removed when he changed to the lin pot he had planned to use.
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