Does my Pass amp dislike my Meridian preamp?


My Meridian G68 (preamp/processor) has been acting up, and my Meridian dealer suggested that the symptoms might be caused by an interaction with my amp, a Pass Labs XA30.5. I have consulted with a trusted Audiogon member, who doubts this theory. So I would like some more input. Here are the symptoms:

1. Meridian G68 freezes up. Neither the remote nor the front panel buttons are responsive. Must be unplugged and plugged back in to work again.

2. After it freezes and I power it down, sometimes a loud “popping” noise is emitted by the speakers.

3. In August, the Meridian G68 stopped working altogether. It was repaired by Meridian America. They replaced the power button and the power supply. But now the symptoms are back.

Thoughts?
bryoncunningham
From the information provided, I'd the say the problem is with the Meridian. I don't think the Pass would cause this issue.
Agreed.

Kal
Ask your Meridian dealer for a more detailed explanation of the "interaction".

Sounds like he's pulling your chain or he's just dumb.

IMO
I would think your issue is in the A/C powerline coming into the Meridian. Spikes or surges.
'might' be possible the amp is causing some sort of current draw problem on turn-on for the Meridian.
Do you use any sort of power conditioning for the Meridian?
My best guess is an electical spike is repeatedly entering your Maridian from somewhere and damaging it.
Or less likely, the problem IS in the Meridian and they replaced a part that got damaged, but what is causing the damage is not fixed in the Meridian.
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.
+4 on the dealer being wrong and I would guess the repair was incomplete, ie the damage to the power supply was caused by another fault in the pre. If the work is under warranty just keep taking it back...
Disconnect it from the amp or try a different amp and see what happens.
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. :-(
what about warranty on the first repair?
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.
Is it possible that the mod has created the problem? Maybe something not done correctly etc.?
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.
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?
Bryoncunningham, its almost impossible to damage a crossover without also damaging the drivers. If there is indeed a crossover failure and the drivers OK, you can be assured that the problem was just in there waiting to happen and it has nothing to do with the amp or preamp.

How do you know that the amp driving the speaker is OK? Did you try it on a different speaker or the speaker on a different amp?
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
Atmasphere,
I agree 'almost completely', which is to say--like lightning damage, virtually anything can happen--but, as usual, you're a fountain of really, really good information.
As to the original question...it's obvious from here in Louisville, some several hundred miles from the problem, lol, that the Meridian is the problem.
'Problems' between amps and preamps are like marital problems, they're usually solved by a third party, which is to say a therapist (or nosey neighbor or friend at a bar) or a lover, (a technician who can 'fix the problem' with a few tweaks--define tweaks however you will in this context,lol)

Larry
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"?
The only thing I can think of is dc offset...but I believe that the Meridian has an ongoing problem--an easy eval from Louisville, KY. (Don't laugh, Ashly Judd has a clause in her contracts that Kentucky has to be mentioned in her movies, and SHE'S cute! Are you?
Anyway, it's almost assuredly the Preamp/Processor that has the problem and unlikely that the Pass amp is backfeeding the preamp something harmful...
Larry
I guess one way to deal with it would be to have the PASS tested by a qualified tech to determine if it is displaying any aberrations. I have one of the best techs in Canada about 10 miles away from me and he has tinkered with various bits of my gear in recent years. When I told him I had bought a c5 year old X-250, his reponse was : "I dont imagine I'll be peeking under the hood of that piece for another 15 years or so'.
Why? I had a Pass amp and one of the transformers got real buzzy right away. I would expect all more from something that expensive!
Parts fail, company reactions SHOULD NOT!

Call Pass Labs immediately and report their reaction to ALL OF US ON A'Gon!
Larry
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?
My first guess would be a PLC (programmable logic controller). Could be socket mounted but more likely replacing a board. Can be intermittent and difficult to track down.
Of course, something, must be passing through the analog level of the pre to the amp, to create a problem for the amplifier--why hasn't anyone else written this?
I normally just 'hide behind others' on things like this, HOWEVER, this is too easy.
The amp is faulty, or the pre is sending something at the analog output which is creating problems.
It's easy... send the pre and the amp back...see who's honest and helpful.
Larry
Hi Bryon,

Sorry to hear of the further problems.

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.

Given that, my initial skepticism that the Pass could be the cause of the G68's problems is now increased to the point where it strikes me as complete nonsense.

If significant dc offset, or some other anomaly, were to have been fed back from the input circuit of the Pass to the output of the G68, it seems unimaginable to me that it would have caused a problem affecting the center channel speaker, to which the Pass is not connected, without also damaging the output circuit of the G68 that drives the Pass.

With respect to applying your multimeter to the problem, what I would suggest is that you disconnect all of the outputs of the G68, turn off all source components which are connected to it, and see if you can detect significant voltage at its output that had been driving the center channel. Try that with both the dc voltage and ac voltage functions of the meter.

Best regards,
-- Al
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)
Sorry, term I meant was PIC (programmable interface controller).
Bryon, 1.0 and 0.7 volts ac should certainly not be present at those points in the absence of signal, but I'm wondering if those readings might be due to meter inaccuracy.

Is the +/- 0.5 volt tolerance really the meter's specified accuracy, or is it the resolution of the measurement, in which case the accuracy could be and probably is worse than 0.5, and might account for the entire 1.0 volt reading?

What reading do you get if you touch the two leads of the meter to two different points on the chassis? Perhaps the meter is responding to emi being picked up by the leads.

Also, were you measuring at rca connectors, or xlr connectors?

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?

If xlr, did you measure directly between pin 2 and pin 1, and pin 3 and pin 1, or was the return lead of the meter connected to some presumed ground point other than pin 1?

Best regards,
-- Al
Disconnect it from the amp or try a different amp and see what happens.
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?
A loud pop can certainly do damage to the speakers, without necessarily damaging the amplifier.

*All* the drivers damaged is a little weird- unless we are talking a smaller 2-way speaker. If it was heavily over-powered by one of these pops, it could have been toasted in a heart-beat.

I would run the G68 for 2 days non-stop and then see what sort of voltages are at the output. 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. If that is true then you may never see anything unusual at the output unless you have some sort of event recorder rather than a simple voltmeter.
Hi Bryon,

You're welcome! Most likely the chassis ground point you initially connected to is directly connected to the rca ground sleeves, and a dc ohmmeter would read essentially zero ohms between those two points. But at high frequencies, that are still within the bandwidth of the meter's ac volts function, there is apparently enough impedance between those points to cause electrical noise, circulating ground currents, emi effects, etc., to produce a measurable voltage between the two ground points.

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

If so, obviously 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.

That is, of course, good practice in any system -- power amps on last and off first.

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. The pops very conceivably contain multiple spectral components, at low, mid, and high frequencies, which would account for the fact that all of the drivers were affected. For instance an electrical pulse, that rapidly transitions from a low voltage to a high voltage, stays at that high voltage for some amount of time, and then rapidly transitions back to the low voltage, contains low frequency spectral components corresponding to the pulse width, and high frequency spectral components corresponding to the transition times (rise and fall times).

Also, I note that as might be expected your Focal's appear to have considerably greater power handling capability than the center channel speaker, which obviously would provide some reduction of the likelihood of damage if they are subjected to similar pops.

Finally, fwiw I too suspect that spending another $800 or so on G68 repairs would likely be throwing good money after bad.

Best regards,
-- Al
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
Q1) I would expect that the Pass amp is designed to tolerate a large amplitude input signal while in standby mode, but presenting that question to Pass would probably provide the best answer.

Q2) Assuming that you don't see any significant voltages intermittently appearing during the two-day test period Ralph suggested, and assuming the pops do not appear when the amps are powered up, and assuming the G68 does not develop any new symptoms, I can't envision a means by which damage could occur.

Best regards,
-- Al
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.
Bryoncunningham, the fact that it sounds better suggests that someone (not you) has not done their homework... I think your approach here is a good move.

If it seems to be OK- you might have the cause narrowed to the computer and the power supply, but 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. FWIW, just because the power supply has been replaced is no guarantee at all that it works right!
...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
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.
Bryoncunningham, try rotating the modules back into the preamp one at a time- let it run for 2 days each. If its one of those boards, you will know which one this way.

If nothing happens, then the power supply possibility is increased and the idea that its one of the removed boards is eliminated.
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
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