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Is my amp damaging my preamp?
Is my amp damaging my preamp?
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Old 8th November 2010, 04:27 PM   #1
bcunn is offline bcunn
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Join Date: Oct 2010
Default Is my amp damaging my preamp?

I have a Meridian G68 preamp/processor and a Pass Labs XA30.5 amp. The Meridian G68 has been freezing up. My Meridian dealer suggested that the problem was attributable to DC leaking into the preamp from the amp via the interconnects. The G68 has been modded. I don't know for sure, but I think that the modder may have removed the AC coupling capacitors. I'm thinking that might confirm my dealer's theory that DC is leaking into the Meridian G68.

Other symptoms:

-When the G68 freezes up, the only way to get it to respond is to unplug it and plug it back in.

-When the G68 freezes up and I power it down, sometimes a loud "popping" noise is emitted by the speakers.

-These same symptoms occurred earlier this year, and after several months, it killed the PSU in the G68. It now has a new PSU, but the problem has returned.

Can anyone tell me if they have every heard of something like this?

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Old 8th November 2010, 04:31 PM   #2
Samuel Jayaraj is offline Samuel Jayaraj  India
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Join Date: May 2001
Location: Bangalore, India
I once had a DC coupled pre-amp connected to a Walkman. It was excessive DC that killed the Walkman in a very short time. Put back the output coupling caps on your Meridian preamp. Hope this helps.
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Old 8th November 2010, 04:37 PM   #3
Aucosticraft is offline Aucosticraft  India
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Location: Pune
PowerON both the amp and preamp. Connect multimeter in between both's ground. Check if there is any potential difference. Ideally it should be zero. Also put a poly cap of 2.2Uf as coupling between them and see if the problem persists.
There is always a first time....
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Old 8th November 2010, 04:45 PM   #4
Mooly is offline Mooly  United Kingdom
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Is my amp damaging my preamp?
All sounds highly suspicious to me. Any respectable output stage (in a preamp) should be able to source or sink a few milliamps at least, something like the meridian I would guess even more. So it would be a pretty major fault on the power amp to put that kind of current back into it's input.

Obviously without seeing either it makes sense to at least check the Pass amp has zero volts on it's input with nothing connected. Be aware of creating severe hum/noise if you leave speakers connected while measuring.

Sounds more like issues or design issues with the Meridian to me.
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Old 8th November 2010, 11:20 PM   #5
bcunn is offline bcunn
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Join Date: Oct 2010
Thanks for the input. I spoke with my Meridian dealer again, and he has changed his mind about the source of the problem. He no longer thinks it is the amp.

I will be sending G68 back to Meridian America for repair.
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