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EQUIPMENT FORUMS >> ZMA >> Newer ZMA owner. Channel balance / center image.
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Message started by __Jon__ on 12/05/21 at 20:02:54

Title: Newer ZMA owner. Channel balance / center image.
Post by __Jon__ on 12/05/21 at 20:02:54

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

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by HockessinKid on 12/05/21 at 20:23:00

Jon,

If you swapped the speaker cables and the issue shifted from left to right, it sounds like it could be the speaker cables are the culprit. I would check to make sure you are connecting + & - connectors properly from your amp terminals to your speaker terminals as what you might be experiencing is inverted phase on one channel.

Also double check your IC wiring as well between your various components, as this also might be the problem.

If your speakers are placed at least 6' apart you should have a nice soundstage with vocals front and centered. Hope this helps.

HK

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by Archie on 12/05/21 at 20:36:20

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.

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by __Jon__ on 12/05/21 at 21:17:02

I just swapped the cables at the amp from left to right. Left the connections to the speakers the same.

I still have the Pass Labs amp. I suppose I could swap it in and check.

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by GroovySauce on 12/05/21 at 21:49:46

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.

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by __Jon__ on 12/06/21 at 17:03:58

Thanks everyone for the input so far!

I spun the volume knob without effect (it's a stepped attenuator and not a pot, although I really don't know how that impacts things in terms of balance).

I tried reversing polarity. When the right speaker is reversed, the image shifts even more to the left. When the left speaker is reversed, things become much harder to localize but still generally to the left (imaging kind of collapses).

I think, as HK suggested, there is an outside possibility that it could be a speaker wire. Unfortunately, my left and right speaker wires are different lengths and the left won't reach the right. This precludes swapping them, at least with the speakers in their current positions. I and a more electrically talented friend built the speaker cables out of similar wire to what Steve uses (8 gauge mil spec silver coated copper, etc), with hydraulically crimped and silver soldered spade ends. Cables are labeled with respect to polarity and channel. I will use this as an excuse to obtain and compare with a different set of wires at some point. ;D

Seems more likely from my troubleshooting that it's somehow the amp. On a positive note, I took Groovysauce's suggestion and was able to play with lowering the left channel on HQPlayer and noticed dramatic improvement (ultimately settling on a -3 db setting). Best things have sounded! I'm still left with a lingering worry of an unsolved problem and that things could be even better, but I am pleased.

I will swap out amps to the solid state at some point and report back.

Thanks again.

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by Archie on 12/06/21 at 17:15:48

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! ;D

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by Lon on 12/06/21 at 17:37:06

You've probably checked them, but when I had this issue a few months ago I happened to check the XLR inputs on my preamp and one was not quite fully seated; with a little push on the connection for it to snap into place the even balance was restored.

Title: Re: Newer ZMA owner. Channel balance / center image.
Post by Carlsbad on 12/15/22 at 04:43:01

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