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Possible [Power?] Amp Malfunction

#21
Bob Lee (QSC) said:
Do you plug your bass directly into the PLX amp?
Click to expand...

Bob: thanks for chiming in.
To answer your question: No.
You guys should give me a little more credit! To reiterate:
I run a Carvin LB70 into a BBE Bmax-T preamp (which I plug my bass in to), which goes into a PLX1602, bridged out to two Aguilar GS112 speaker cabinets. I run a patch cable between the pre and power, a speakon from power to speaker cabinet, and a speaker cable from speaker cabinet to speaker cabinet.

Tonight at rehearsal I had pretty bad problems again. I'll play normally and it will POP, I'll lose volume and it will sound like snowing through my tweeters. It seemed to go away momentarily when I sent a super hot signal through my bass by slapping the strings. I'm 90% sure it's the poweramp, I haven't yet had anyway yet to test the preamp by itself, but I am sure it is not my bass (I tried another bass).

Though I appreciate the help I've got from you fine folks, I'm more concerned at this point with where I need to go to get my amp serviced than more troubleshooting tips, as I believe going from here I don't have the necessary equipment to isolate the problem further or fix it myself. is there anyone on here in the Portland area who would be able to help me diagnose the problem? Money is a real issue for me right now, this could not have come at a more inconvenient time. If no one knows anyone in the Portland (or better yet, Corvallis) area that could help me out, what shop would you recommend for diagnosing and fixing the problem for as little money as possible?. I don't mean to sound cheap, but I know you were all 22 once, I bet you know what's like to be broke.

Thanks so much,
-David
 
#23
Have you tried unplugging the patch from the preamp TO the power amp when it is "hissing" If the amp keeps hissing with nothing plugged into it then it IS the amp.

If it shuts up with the cable removed then you need to have your preamp looked at.

An amp tech will do the SAME thing before he even opens the case. Do you really want to pay for him to do that only to tell you there is nothing wrong with it?
 
#25
I really appreciate you guys getting back to me, I wish I could have figured out to try this before I took it in. unfortunately I live too far away from Portland and only have limited time when I'm up there, and I had other things to do today so I had to just bite the bullet and take it in. I wish I had tried what you guys suggested, I just plainly didn't think about it...I spent more time today worrying about where I could take it and be actually able to talk to some one about it before I dropped it off...I ended up not being able to talk to any repair tech at all, only able to drop it off, not having a choice really with a very important gig coming up and being IN portland at the time. Wish I had checked this, because if it is the preamp, there was no reason to give them the $60 (of my friend's money that I'm borrowing) for the deposit.
 
#27
Update: Still unable to talk to the actual person who "worked" on my amp, I get a call today, finally. Your amp is ready to be picked up. What was wrong with it? No problem found (as you guys predicted:rolleyes:) though they went over the power amp dusted and cleaned and checked everything, as well as cleaned the effects loop in the preamp which they said sometimes causes intermittent problems like the one described. The girl was unable to tell me if they could even reproduce the problem. $60 of labor charge, I just hope it frigging works. I wonder if they tried changing out the preamp tube? I would bet money they could not reproduce the problem, I really hope it's fixed.
 
#28
Update: Got my amp back tonight, everythings kosher. My bet is it was a dirty effects loop in the Bmax-T preamp. I also replaced the stock GrooveTube 12AX7 with a GT 5751M tube after practice and as I was taking the cover of the preamp off I was thinking to myself the whole time "wow, if I had known that it was the effects loop, I think I could have cleaned it myself, likely costing less than the $60 I paid the shop :rolleyes:.s
 
#29
Hey, now you know for next time so it's all good. I think that was highly excessive to charge you the full $60, though. Probably spent 15 minutes on it tops. $30 would have been a more fair figure.
 
#30
JimmyM said:
Hey, now you know for next time so it's all good. I think that was highly excessive to charge you the full $60, though. Probably spent 15 minutes on it tops. $30 would have been a more fair figure.
Click to expand...

Yeah, it is nice knowing that everything in my poweramp AND preamp is in good working condition, dust and dirt free, though I bet they spent an hour on everything. $60 an hour seems kinda high though.
 

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