2. amps-preamps
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need help with Conrad Johnson preamp SNAFI

Hi folks,
Am seeking tips from wiser heads.

I have a conrad johnson preamp pv10 and a cj power amp premier 11a. I bought the power amp about a year ago. I had the preamp serviced to above-grade condition by one of the names regularly referred to here at the king of CJ repairs and upgrades. Have not used the pair more than 500 hours in the past year.

Anyway, first I turned on the power amp. No problem. Then I turned on the preamp (connected to power amp). As soon as the warm up, the red "bias adjust" lights on the power amp started slowly blinking two at time (the outer two, then the inner two). While that slow blinking happened, a perfectly synced low sound came from the speakers, blurping in time with the blinking lights.

I unplugged the speakers: still blinking. I tried a different preamp and the blinking/blurping on the power amp stopped. But it's a Linn solid state preamp (actually an integrated amp I'm using as a cd/preamp for this experiment). I really really prefer the profoundly musical CJ sound.

After unscrewing about a dozen screws, I opened the preamp up (unplugged of course). No scorching or obvious problems. Umm, I can't tell what a bad tube looks like, and these tubes are really snugly installed. Is there something I should be able to see?

Action item: Should I just buy a new tube complement for the preamp (not a cheap thing, but necessary for the long run if I keep the preamp), try those out, and THEN (if needed) send the preamp to Virginia for repairs?

OR, is this blinking/blurbing phenomenon when the preamp is connected to the power amp NOT symptomatic of a tube problem but of something more electronic (voltage, etc)? I hadn't heard any prior audio problem that could indicate tube degradation.

Thanks for any tips!!
paanders
6 responses Add your response
paanders OP
43 posts
 
When I spoke to a dude from CJ on the phone, he seemed pretty confident it was a power supply issue in the power amp. So I'll send along to Bill Thalmann at Music Technology, since he struck me as a great guy on the phone and his reputation couldn't be higher.

I wrote this partly for future readers, should they have a similar problem someday.
pops
2,273 posts
 
Sounds like the preamp is the problem, it could be passing DC, or it could be some sort of arcing in the preamp that is being passed on to the amp. This happened to me once with a CJ premier 14, it turned out to be a loose solder joint at the tube socket. It was kicking on the protection circuit on my amp. Good luck - I would send it to CJ.
paanders OP
43 posts
 
Thanks for notes. I did try to rebias. No improvement. All works fine with different preamp. The noise emitted when the cj preamp is plugged in is not affected by volume control. So that's perhaps a sign of line stage power issues?
yogiboy's avatar
yogiboy
5,661 posts
 
You stated that you unplugged the speakers. You should always
leave the speakers hooked up to a tube amp(needs load). Just
some information for future testing.
mofimadness's avatar
mofimadness
4,982 posts
 
As Steelhead stated: ALWAYS preamp on FIRST, then amp. Reverse this at turn off.

I would try what Steelhead suggests and re-bias the amp. The preamp might have whacked out the bias a little when it come out of auto-mute.
steelhead
318 posts
 
First preamp on first. Then power amp. Reverse when powering down.

My cj 12's exhibited the same issue you describe. I adjusted the bias individually and basically ignored the random traffic light on/off after bias and it lasted a few hours and then stopped. (did not have sound coming through the speakers though)!!!

If the blinking had not gone away I would have had to go to a tech. I suggest getting in touch with whoever did the work (Bill?) as he would be the guy you want to get the advice from.

Good Luck.
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