Does my Pass amp dislike my Meridian preamp?

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