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I have no preamp. My source is unbalanced and I would like to use the “RCA to XLR” cable method. Can I add a potentiometer and retain some of the benefits of this connection method?
A: Indeed you can. There’s no good way of adding a potentiometer to a truly balanced connection, but in a “pseudo balanced” connection it is possible. You'll need to use microphone cable (shielded twisted pair). There are 2 stretches of cable. Cable 1 goes from the RCA terminals to the pot. Cable 2 goes from the pot to the UcD input.
https://www.diyclassd.com/FAQ-Hypex/Cables-and-connections/I-have-no-preamp.-My-source-is-unbalanced-and-I-would-like-to-use-the-RCA-to-XLR-cable-method.-Can-I-add-a-potentiometer-and-retain-some-of-the-benefits-of-this-connection-method
1) Cable 1 (RCA end): shield and white wire to RCA ground. Blue wire to RCA signal.
2) Cable 1 (Potentiometer end): white to potentiometer "common". Blue to potentiometer "input". Shield of cable one is connected to shield of cable 2 AND TO NOTHING ELSE!
3) Cable 2 (Potentiometer end): white to potentiometer "common". Blue to potentiometer "output" (wiper). As said in 2) the shield connects to the shield of cable 1 and to nothing else. RESIST ANY URGE to connect the shield to the pot common. 4) Cable 2 (amplifier end): white to pin 1, blue to pin 3, shield to pin 2. So that means that the shield of cable 1 continues as the shield of cable 2, so you get a contiguous shield all the way from the RCA to the amplifier. Any circulating currents that go through the shield will never mix with the audio ground because the audio ground is kept separate (white wire) and sensed differentially by the amplifier.