Greetings forum. I have enjoyed many of your posts for the last year as I waited for my ZMA and eventually explored tube rolling. Was hoping some of you might help me sort out a problem.

I have a single-ended ZMA, with stepped volume control and the 25th-anniversary mods. I am streaming (via Roon and sometimes HQPlayer) from a fanless custom PC I built via fiber optic to a Sonore Signature Rendu, into a Lampizator TRP via USB and then directly into the ZMA over RCAs. I am currently using Phillips ECG 7027a's as power tubes, Tungsram A03s, and a pair of NOS 1960's Amperex and Mazda 7308's for signal tubes. I have a pair of Salk Exotica speakers with RAAL tweeters and a SEAS Alinco midrange drivers. I find the sound is excellent and a real upgrade from my prior solid state Pass Labs amp (which I also liked).

Here is the problem I have been having. Voices are consistently centered about 10 degrees towards the left and the left speaker seems to have a bit more of everything going on compared with the right. Subtle, not dramatic but reproducible between recordings / artists. Subjectively, the right channel sounds just a little quieter and also measures a couple db lower than the left (calibrated microphone using Room EQW and pink noise).

I swapped the speaker cables and the off center voices shifted to the right (to me eliminating the speakers and placement issues as causes). I swapped all of the tubes individually left to right in the Lampy and the ZMA without change. I also swapped the RCA cables left to right and tried different cables and the center voice remained consistently slightly to the left (to me eliminating the DAC, streamer and computer as causes). I haven't repeated db measurements with the microphone in all of the above scenarios, but the changes are audibly obvious once noticed. The above would seem to me to point to an issue with the ZMA, but I'm not sure what or if additional trouble shooting would be helpful in confirming. I have the ZMA volume somewhere around 2/3rds use the Lampy for volume control (as it has a remote control). I changed the volume a few stops on the ZMA  in both directions (and compensated on the Lampy) and didn't notice any change in the degree of off-centeredness.

I plan to ask Steve but I thought I would run it past the forum and more experienced audiophiles first. Any ideas?

Best,

Jon

I took it to mean that he just swapped one end of the speaker cables.  What would be better would be to swap the speakers left to right leaving the cables as is.

With no music playing spin the volume knob from min to max a few times. Maybe there is a speck of something on the new pot?

Try inverting the polarity on one set of speaker cables. + to - at only ONE end either the amp or the speaker. Making one speaker out of phase.

Do you have a way to adjust L to R balance in small increments? HQplayer does have this ability. How much do you need to adjust to get the image centered?

I can adjust in 1db increments and constantly need to have it 1-3db to the left depending on tubes. My room doesn't have equal walls so it messes with the sound stage.

To rule out the speaker wires, can you get same lengths of common lamp cord wire and try that to see if the image shifts?  Of course, the danger with this is that you could fine out that lamp cord is just as good as high $ wire!  

Jon
Don't know if you ever figured this out.  My thought is that it is likely speaker placement.  The ZMA is an excellent imaging amp and if one speaker is a bit closer to the listening chair than the other, or at a different angle, it will move the center image.  this is how I tune my speaker position, I move them in and out until the image is in the center for center sounds.
Jerry