For more than a month now, I have been chasing my tail trying to get spot-on channel balance. Before my AI preamp got smoked,I used to get the balance by adjusting the separate volume controls ( I now know this is not exactly the right way to do it). With the replacement Seduction preamp there is no way to set the balance independently, I had to suffer through vocalists singing a bit left of center. I did the usual rituals of swapping, substitution, speaker relocation, room treatment, etc,etc. What made matters worse is that the problem was not gross,I even suspected it to be intermittent, either due to equipment or my very own EARS! There are just so many possible sources of problems from contacts, tubes, interconnects, SUT, speakers, room, etc. It is overwhelming, after a month, I was no closer to the solution.
The best way then, I thought is to isolate the problem through elimination, starting from the speaker/room, all the way back to the source. STEP BY CAREFUL STEP!
I made up a tool which has proved indispensable in isolating sources of imbalance. It is a simple signal splitter. A signal is fed at the input, the output being two exactly identical signals. The parts used are 2 capacitors (.1 mfd each), 2 RCA jacks, 1 RCA plug and a capacitor can:
I started by feeding one channel (left or right does not matter) to the splitter and feeding the output to the inputs of the amplifier. This tests the amp-interconnect-speaker-room chain. Amazingly (and luckily) the image snapped to DEAD CENTER! I left the set up for a day's listen to be sure of what I am hearing. It was true, the problem DOES NOT originate from the amplifier onwards, the signal comes unbalanced as supplied to the amp input!
Now, that's settled with finality, I will be moving on to the preamp section, then all the way back to the source if necessary. To paraphrase Sherlock Holmes...if all possibilities have been exhausted, what remains must be the answer no matter how improbable.