Does my Pass amp dislike my Meridian preamp?

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

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

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

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