Does my Pass amp dislike my Meridian preamp?

I doubt the mods created the problem, because the symptoms are identical to what happened earlier this year leading up to the power supply failure in August, which all happened BEFORE the mods.

Thanks for the input so far.

Elizabeth - The Meridian is plugged into a Shunyata Hydra 8, as is the amp and the rest of the system. The Shunyata is on a dedicated line.

Waiting to hear from my dealer. I will report back with further details.

Just heard back from my Meridian dealer. He has changed his mind. He no longer thinks the Pass amp is causing the problem, which seems to be the nearly unanimous opinion here.

I will be sending the unit back to Meridian America for diagnosis and repair - the second repair for what is likely the same problem. Unfortunately, the unit is out of warranty. :-(

About a week after I received the G68 back following the first repair, I sent it off to be modded. The mods turned out great, but now I have voided any warranty associated with the first repair. I should have waited longer to see if the issue reappeared after the first repair. I just assumed that, because it was fixed, it would stay fixed. That was a mistake.

Things just got a little more complicated. The center channel, which is hooked up to the Meridian G68, but not to the Pass Labs amp, has developed a problem. It has distortion that was not previously there. It sounds almost like a bad driver, except it is coming out of all the drivers (I tested this by unplugging the various drivers).

The distortion is not coming from upstream components, because I swapped out every upstream component, and the problem still persists. Therefore, I believe that the crossover in the center channel has been damaged.

Perhaps this is a coincidence, but that seems a bit unlikely. It seems more likely that, whatever is wrong with the G68, it has caused damage to the crossover in the center channel.

Does anyone have an idea about what can damage a speaker's crossover?

Larry - I have already contacted Pass. Their helpfulness, openness, and expertise has been nothing but exemplary. They are skeptical that the amp is causing the problem.

Short of sending the amp back to Pass to confirm that everything is working properly, does anyone know if there is anything I can do to test the amp myself?

If I understand correctly, the G68 feeds left and right preamp-out signals into the Pass, and a center channel signal to a separate amplifier which drives the now damaged center channel speaker. And the signal path through the Pass to the left and right main speakers continues to function ok, apart from the intermittent freezeups in the G68.

This is all correct.

I used my multimeter on the Meridian G68 outputs and the Pass amp inputs, and here are the results:

Meridian G68 outputs:
DCV = 0
ACV = 1V (accuracy of meter is +/- .5ACV)

Pass amp inputs:
DCV = 0
ACV = .7 (accuracy of meter is +/- .5ACV)

Update: I have left the G68 powered up continuously for about two weeks. It has not frozen in that time. It seems that I am out of the woods.

In light of that, the answer to my original question, "Does my Pass amp dislike my Meridian preamp?" is an unequivocal NO. My Pass amp had nothing to do with the problems with my preamp. Many of you suspected as much, and you were right.

Thanks again to everyone for your help and advice. Much appreciated!

Bryon

My guess though, based on what I have seen in this thread, is that the power supply is failing intermittently and is the source of the pops and freeze-ups.

The power supply was recently replaced with a new one from a different manufacturer, and the freezing/popping problems persist. So while the power supply may be a variable in the problem, it doesn't seem like it's the whole equation.

I would run the G68 for 2 days non-stop and then see what sort of voltages are at the output.

I will do this. Thanks for your input, Atmasphere.

Do the pops occur only when you disconnect and reconnect the G68 from its ac supply, to recover from the freezeups?

I can't remember for sure, Al. My best recollection is that the pops occur only when there are freezeups, but I could be wrong about that.

...they can be avoided by first turning off the power amps, then waiting perhaps a minute or two for their stored energy to dissipate, before disconnecting the G68's power. And reconnecting the G68's power before turning on the amps.

I know this rule, but I haven't always followed it, out of carelessness. I will be far more careful if I decide to keep the G68 in the system.

My guess, and that's all it is, is that the damage to the center channel speaker was indeed caused by those pops, and is not just coincidence.

I think you are right, Al. If the pops caused the damage to the center channel, then I understand that I can avoid further damage by strictly observing the amp-on-last-and-off-first rule. But this leaves me with two questions:

1. If I turn the Pass amp into standby (i.e., the capacitor banks are still charged), and then turn the G68 off, and the G68 sends a pop into the amp, could that potentially cause damage to the amp? In other words, must I turn the amp off at the rear panel switch to be safe?

2. If I take precautions to avoid the pops from the G68, is there some other way it could damage the amps or the speakers during regular use?

Bryon

Thank you again, Al. I have put the G68 back in the system to test it. I will report back with my findings.

Another development: I spoke with the G68's modder yesterday, and he had a simple theory to explain why it might be freezing up: heat. Other than the analog output stage, the G68 is basically a computer. And it packs a lot of circuitry into a small space. So maybe it exceeds its operational limits and freezes.

With that in mind, yesterday I did some modding of my own: I removed all the video circuitry, the multizone circuitry, and the tuner, none of which I use. The G68's architechture is modular, so this was actually quite simple. Altogether, I removed about 1/3 of the total circuitry of the unit. I left the lid off for maximum cooling and placed it back in the system. I played some music through it to make sure that it still works and, to my surprise, it not only works, it sounds audibly better. The sound improvement was obvious within about ten seconds.

Now that it is operating under cooler conditions, I am going to run it continuously and see if it freezes. I will also test the outputs after two days, as Ralph suggested, to see if I can detect anything unusual.

Update: I have left the G68 powered up for several days and retaken the measurements at the outputs. There is no AC or DC voltage coming from the outputs.

The G68 has not frozen up since I removed half the circuitry and left the lid off. That is consistent both with the heat theory and with the bad PCB theory.

That is a good idea, Ralph. Before I do it, I'm going to let it run continuously for a longer period of time - maybe a week - and see if it freezes. Thanks again for all your help.

Bryon

Atmasphere - I don't know whether the drivers are ok. I can only say that the distortion I am hearing is coming out of all the drivers. It was on the basis of that that I concluded that the crossover was damaged. But the drivers may very well be damaged as well.

The amp driving the speaker seems ok, as I have run it to a different speaker and do not hear the distortion. I also tried the problematic speaker with a different amp, and the distortion was present. So it seems like it's the speaker that has the problem.

My larger concern is that whatever has been causing the G68 to freeze up and to make "popping" noises through the speakers is also damaging the speakers. The center channel was the first to show it, but I'm afraid that the FR and FL are next.

Bryon

After hearing about my damaged center channel, my Meridian dealer has returned to his theory that the cause of the problem is some kind of "leakage" out of the Pass Labs amp.

I have a multimeter. Are there measurements I can take at the amp's inputs to see if there is some kind of "leakage"?

If rca, did you connect the return lead of the meter directly to the ground sleeve of the rca jack being measured, or to some other presumed ground point, such as chassis?

This was the problem. When I took my measurements yesterday, I connected the return lead to the chassis. When I took the measurements again today, this time with the return lead connected directly to the ground sleeve of the rca jack, the measurements were well within the noise floor of the meter, i.e., fluctuating between 0ACV and .2ACV for both the preamp's output and the amp's input. Thank you, Al, not only for being smart, but also for being able to think like a dummy like me. I will now never forget the phrase "presumed ground point."

It is worth noting that the problems with the Meridian seem to appear when it is powered up for several days at a time. In light of that, I think I will leave it on for a day or two, and then retake the measurements at its outputs.

As far as the diagnosis of the problem, it is appearing less and less likely that my Meridian dealer is correct in his theory that the Pass amp is the cause of the problem, which is consistent with the doubts expressed by many people here. Another relevant observation: I am unaware of Pass customers experiencing reliability problems with the XA30.5, but I know of several Meridian customers experiencing reliability problems with the G68, including several folks whose G68 power supplies have failed. That is circumstantial evidence, but suggestive of the locus of the problem.

I have decided not to return the G68 to Meridian America after all. I am not confident that they can fix the problem, and I do not want to spend thousands of additional dollars for them to attempt a fix (the first repair attempt was $800). Even my Meridian dealer warns that spending more money to try to fix this problem in the G68 might be, to use his words, throwing good money after bad.

So here is MY PRESENT DILEMMA: I would like to simply leave the G68 in the system and get all the remaining life out of it, especially in light of the fact that I just spent $800 on a repair and $1200 on mods to the unit. Then when it fails, in six months or a year, I can rebuild the system with components from other manufacturers. However, my fear is that, by leaving the G68 in the system, I will be risking damage to other components. That fear is based on the recent damage to my center channel.

To decide on the best way to proceed, I need to figure out whether the G68 caused the damage to the center channel, or whether the failure of the center channel is a coincidence. Could the loud "pops" that occasionally make their way to the speakers have damaged the center channel? Or could the G68 have damaged it in some other way?

Anyone have any thoughts about these last questions?

...the possibility also exists that it could be a defect in one of the modules that is locking up the computer or draining the power supply.

With that in mind, I think I am going to remove more excess circuitry from the unit. The fewer modules in place, the better the odds that the defective module, if it exists, will be out of the loop. If this works, it will be the solution to the Gordian Knot.

Thanks again, Ralph.

Bryon