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My pre-amp overloads my amp

I just bought a used Conrad Johnson PF-R pre-amp. I hooked it up to my Citation 7.1 amp and everything was fine for the first 10 minutes or so. Then my amp clicked off, the red protection indicator light glowed, then the amp came back on. After a while the same thing happened. I stopped playing music and the same thing happens even when no music is playing. Tried it again the next day (not playing anything) and the same thing happens, the amp goes off, then comes back on. The amp works fine with both my other pre-amps so I know the problem is with the CJ. There are no switches or adjustments of any kind that I can see other than the input and output jacks. I'd like to get some idea as to what is going on before I call the seller (Audiogon member)

Thanks,

Steve
say811
sean
6,231 posts
 
I wonder if the preamp is passing DC into the amp ? This could cause the amp's protection circuitry to trigger, giving you the aforementioned problem. Anybody else got any ideas ? Sean
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drtmth58
66 posts
 
I agree with Sean. The fact that the problem with the CJ occurs even when there is no music playing suggests excessive DC offset; or some other oscillation related difficulty that is triggering the amplifier's protective circuitry. One other possibility, though admittedly a very remote one, is that some exotic and/or poorly designed interconnects might have electrical properties that, in combination with the preamplifier, are also the cause of the oscillation. Obviously, trying a new pair of interconnects is a fairly easy thing to do.
newbee
4,751 posts
 
sean may well be right. i don't know if your amp will pass dc. some ss units do. if your unit does, or if you put in another amp that does, you could pass dc thru to the speakers and fry them! i'm not familar with your pre-amp but if its tubed it could well be that a failing tube is causing a dc offset.
plugged
28 posts
 
Three possibilities that come to mind...

One, your preamp may be passing D.C. This is a bad thing and if it turns out to be the case, it is a good thing your amp has protection circuits since this is a great way to blow things up in a most spectacular and amusing fashion. It is the least likely problem, but potentially the worst. CJ makes a good product, so this is the least likely scenario.

The second potential problem off the top of my head would be a bad output jack with an intermittant ground connection. If you are running the Citation bridged, then it is particularly sensitive to this (Also, if you are running bridged, double check the bridging connectors...if they get knocked loose, the amp will do exactly what you are seeing). Try swapping the interconnect cables you are using and see if that alleviates the problem. You might try some contact cleaner for giggles. I would also check to make sure there isn't a short in the speaker cables that may have been triggered when you moved things around to hook up the CJ.

Third, your new preamp could be overloading the input of the amp...but that would usually only happen at higher volumes. If the amp only shuts down when you start to turn things up...see how long it will run at low volumes. There may be a way to adjust the output gain on the PFR...I'd contact C.J.

Kevin
The Sound Broker
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