Does my Pass amp dislike my Meridian preamp?

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!