Phoenix Gold Phorum

Hi

Im using my 2 front channels to power my focal K2P comps passively. rears not in use.

Was installed a month ago and sounds fantastic, that is til a few days ago when i was driving and noticed an imbalance in the sound. The right side was louder. Stage sounded like it shifted to the right.
When i turn up the volume the right side plays perfectly. Loud, clear and detailed, but the left sounds like it distorts a bit when it reaches 3/4 volume.
The problem is intermittent. Comes and goes. Yesterday up to this morning it was perfect, and a few mins ago is started acting up again. When i go back to the car later and check it'll probably be fine again, but for how long?

Did a check of my T/A, and it's on my usual setting. I checked the Balance on the HU and it was dead centre. Swopped the RCA's around - Still the same issue.
So all is just as it was when installed and sounding perfect.

Any thoughts on what it could be? Any troubleshooting i can try?

try switching the amp channels from left to right to see if the drop in level switches sides to work out if its amp or speaker/cable related

as he said swap the speaker wires on the amp and see if the problem stays the same, moves or goes away. Need to isolate if its the amp, or down the line further

i'll try this tomorrow morning, or the next time the problem arises.

Could be a pot issue.

imo1 wrote:Hi

Im using my 2 front channels to power my focal K2P comps passively. rears not in use.

Was installed a month ago and sounds fantastic, that is til a few days ago when i was driving and noticed an imbalance in the sound. The right side was louder. Stage sounded like it shifted to the right.
When i turn up the volume the right side plays perfectly. Loud, clear and detailed, but the left sounds like it distorts a bit when it reaches 3/4 volume.
The problem is intermittent. Comes and goes. Yesterday up to this morning it was perfect, and a few mins ago is started acting up again. When i go back to the car later and check it'll probably be fine again, but for how long?

Did a check of my T/A, and it's on my usual setting. I checked the Balance on the HU and it was dead centre. Swopped the RCA's around - Still the same issue.
So all is just as it was when installed and sounding perfect.

Any thoughts on what it could be? Any troubleshooting i can try?

this is a typical zx issue, a friend of mine had this problem i quess a year of 4-6 ago.....

nothing was damaged internally, it was just a matter of the settings of bias and dc offset current who had to be set right again......

I personally suggest here you contact Eric D or Valeks for this issue, don't try to adjust it yourself if you don't know what you are doing......

if you are living in the usa of course.....


not much people know that typical for the zx(and zpa) series, that after some years, they need a checkup to set bias and dc offset again good......

and the difference in sound/dynamic and power before and after, is very huge !!!!!


good luck with it.....

of course every issue is diff, so there could also be somewhere a bad solder contact. about the gain pot, turn it 20 times open and close and see

if something changes but i'm for sure the problem will be what i stated in the beginning....... don't leave you're sleep for it........

This troubles me. I'm not sure how the bias and DC offset adjustments can have HUGE effects on power and dynamics. I know they affect distortion levels at low volumes. Are we talking high end hifi terms here?

I have a ZX450 but I don't use it. I prefer M50 for my comps and MS275 for subwoofer because of their simplicity and lack of unnecessary controls and crossovers.
Do you know if M or MS series suffer from bias / DC offset problems?
I have measured DC offset but bias is beyond my measuring capabilities.

Mr. Wild wrote:This troubles me. I'm not sure how the bias and DC offset adjustments can have HUGE effects on power and dynamics. I know they affect distortion levels at low volumes. Are we talking high end hifi terms here?

I have a ZX450 but I don't use it. I prefer M50 for my comps and MS275 for subwoofer because of their simplicity and lack of unnecessary controls and crossovers.
Do you know if M or MS series suffer from bias / DC offset problems?
I have measured DC offset but bias is beyond my measuring capabilities.

believe, or don't believe me..... but it is the truth......... same story with the zpa amps........

Both the bias adjustment and the DC offset are not critical. Yes, they are important, but not "critical".

Very few amps have DC offset adjustment (ZPAs do), so they vary a bit with their offset. Also, the temperature of the amplifier affects its DC offset (depending on design). In the case of the ZPA, it is much different warm or cold, and therefore you can never set its adjustment perfectly.

Bias is similar, its setting will be different if the amplifier is warm or cold.

All the bias does is adjust the level of Class A current in the output stage. Class A/B amplifiers operate in Class B for most of their signal, and the Class A component is to improve crossover distortion (when the signal crosses over from the top of its sine wave to the bottom.

The fun part is most amps use a lot of feedback in their designs, so the feedback itself helps to remove the crossover distortion.

Here is a challenge for the brave. Take your amp and make note of where the bias controls are as precisely as you can. Turn them all the way down. Now listen to the amplifier. Let me know if is sounds any worse. When done, put the bias controls back where they were.

I personally can't tell the difference between no bias and a properly adjusted bias on a PG amp. I suppose if you run the amp on 1 ohm components or at very high output levels the crossover distortion may come into play, but at reasonable levels on 4 ohm components, it does not sound any different to me.

When I repair someones amp which has a blown channel, I listen too it prior to adjusting the bias anyway to make sure it sounds fine. Then once I adjust the bias I listen to it again to make sure it still sounds good.

Even on an oscilloscope it is hard to see the benefit of bias adjustment on a PG amp. You can start seeing some crossover distortion while under load, but it is really pretty minimal due to the feedback.

Now, I am not advocating you run your amps with the bias down. The distortion figures on the amp are improved by setting the bias correctly, and everyone might as well get the most performance they can from what they are using. I would never run amp amp with the bias down in my vehicle, nor would I expect anyone else too. All I am saying is the setting is really not that critical, and so long as you don't have it set too high (overcurrent and amp failure result), you don't have much to worry about.

Thanks for the input , Eric.....

the only thing i wanted to state, and i don't want people to get me wrong, so indeed my friend had the same one channel

issue with a zx450, so at that time, i took his amp out(after reversing channels and rca of course) and took at the same time his other

zx450 who was playing (normal without issues) on two subwoofers.....

well, so i brought them in here at my technician, when i got both back, i connected them again in the install, of course the

one channel was fixed, and the install played so more better then, especially the subs, it was like double the bass then before....

with the same amps.... i asked after to my technician, what components were damaged, what did you change ?? the answer was,

nothing was bad, it was just a total adjusting and setting again of bias and dc offset, was the answer......


last year i had a zx500 in a trade, recapped it myself and let it checkup and put bias and dcoffset back good again....

some time later i bought a simular zx500 off ebay (to have two) and when i made a comparision of both on subwoofers, almost at

full power, i could here a good difference in power and dynamic output between the serviced and the (not yet) serviced amp......

so my opinion it is a good thing to let the amps checkout again by a good technician (like Eric D ) before starting with them in a new install......


I don't adjust bias and dc offset myself, because this is above my knowledge.....i have my technician here to do so........

i only replace ps caps......


it is just a personal experience i have i love to share with other people.....

off course everybody feel free to decide if it's important for you or not.......

I appreciate any and all advice. How awesome is it to have a forum dedicated to your brand of gear, and have knowledeable members give advice based on proper experience of your product, and not random thumbsucks, just to post something.

Thank you all!
PG - great brand - Awesome sound - great support!

I Still haven't gotten around to do the trouble shooting to the gain pots, like some of the guys here, and eric on email, suggested.
Work keeps me busy til late, but i'll try tonight. i hope just its a corroded pot that i can work clean with a few(or many) turns.

It has happened to me too. When a pot hasn't been touched for years it can cause a channel to cut out or fade. Turn the pots back and forth a few times.
If all else fails you can just use the rear channels of the amplifier.

I did this yesterday and i believe it's 95% better, if that's possible. I tested using my reference cd and it slightly still pulls the stage to the right.
so i think we on the money with this troublehooting step. The scratchy distortion at 3/4 volume was not audible, so i'm happy about that too cos i was worried about damaging these nice speakers.
Thanks to all again for the help.

I'll give it another round of fiddling this weekend, and keep the rear channels as my last resort. Even tho i'm not using all the channels, i'd like to know that they all working perfectly.