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Krell preamp / Parasound amp power up issue

Hello everyone,

I recently purchased a Krell S-1000 preamp which sounds amazing when mated to my Parasound A51 amplifier. I'm having a few issues with the system, though. Here's what happens:
1. I power up the Krell, it triggers the Parasound with a short delay
2. Just as the Parasound is powering up, there appears to be some sort of spike/short, a low level thump will come out of the speakers
3. As this spike/ground loop/thump occurs, the Krell preamp will shut down,in turn powering off the Parasound because the trigger turns off

If I power up the Parasound first, there isn't an issue. Also, this doesn't happen every time I turn on the system, only sometimes. There's a ground lift switch on the back of the Parasound, I've tried both 'lifted' and 'grounded', get the issue on both settings. Also doesn't seem to occur when I use RCA cables, but there's less hum on the XLR connections and they sound considerably better, so I want to stick with the XLR connections.

I upgraded from an Integra DHC-80.2 also connected with XLR and it didn't have this problem.

My next plan is to try a two prong plug on the parasound. Anyone else have other ideas?

Thanks!
Chris
128x128cjwessing
sfstereo
215 posts
 
Here's my guess:

When the amp turns on, your AC line voltage sags for a very short period due to the inrush current which will cause a glitch with the Krell processor.
Once the processor experiences a glitch, it can do strange things like being locked up or resetting itself which the Krell seems to be doing by shutting down.

You don't have this problem when the amp is turned on first since the line voltage has recovered by the time you turn the Krell on. You can verify if this is the case by plugging a lamp in the same outlet as the amp and see if the lamp dims briefly when you turn the amp on.
cjwessing's avatar
cjwessing OP
32 posts
 
You guys are correct. I called Krell to ask about the issue, and his first question was "Are you using a power conditioner?" And yes, I am using a PS Audio Premier active conditioner, and it can't provide enough current when the amp turns on. The Krell senses the drop in current and shuts itself off.

Plugging the Parasound amp directly into the wall fixed the issue.
dhl93449
455 posts
 
You might also check that the surge current limiters in the A21 are OK. These are supposed to limit the inrush of current to the main power supply capacitors during turn on. Not sure about the A21, but the early design JC1s typically have surge current limiters that go bad.
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