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Need HELP-Troubleshooting weird balance and hiss issue on Parasound 2100 preamplifier

Ok
Bear with me on this weird issue.  Last year I forgot to turn off my amp as I switched out my left speaker and  I crossed positive and negative wires. After the loud pop sound the only thing I could determine as far as damage seemed to be, as impossible as it sounds, on the preamp. Now every time I first turn on my preamp I would get a loud hiss that would slowly die out after 15 seconds. The left channel also seems to have a significant drop on output. ( It follows the channel as I can move it to the right speaker by swapping interconnects). Switching speakers -amps-cables ect...does nothing but show its from the preamp -I assume its output stage. Local service bench tested it out and could not replicate hiss. For the out of balance issue I can apply pressure downward on the balance knob and will even out the right and left channels. This is crazy but I actually have temporary piece of plastic shoved in to the slot to keep it even. Does any of this story sound familiar and does my temporary fix make any sense? Can 
azthu
azthu OP
24 posts
 
I appreciate the help.
Of note I have had the factory tech guys at Parasound check it out and they didn't find anything out of sorts.  This tells me it is something very rare and weird. I wondering if the entire balance mechanism requires a change out. Maybe then the hiss will follow.
213runnin
914 posts
 
Wow that's a strange one.  If the tech guys at Parasound couldn't find out why the balance was off, then you really are out of luck.  I would have thought they'd suggest replacing the balance pot in that case.
atmasphere's avatar
atmasphere
11,793 posts
 
If the preamp is balanced it could be missing a phase. This would explain the increased noise floor and less volume both at the same time.

Sounds like something to do with the balanced control is damaged- possibly a broken trace or solderjoint on the board that retains the balance control. You will need technical help to solve this- and Parasound seems your best bet.
1953questions
1 posts
 
Hey Asthu, any luck with that issue? I have the same thing happening with the balance knob needing pressure to work. And my 2100 was spiked with the wrong signal when I connected a Phono preamp accidentally to the 2100 input that had the MM phono switch turned on! Yikes - double the power. Thing went pop! So did a tweeter.

I just pulled the pot and am trying to find the part. Wasn't hard to do.
azthu OP
24 posts
 
OK-You are not going to like the answer......
As I was not able to get the issue permanently fixed easily, I ended up buying a second 2100 from Ebay.  Believe it or not, ended up with SAME issue. I finally took both units into an authorized service center for a final diagnosis,and after not being able to ID the issue,  I took his advice and had him take the balance out of the signal path all together. Problem fixed but no more balance control. As I never used it for day to day left /right  adjustments, it was a relatively painless and cheap fix, but I sure wish I had been able to figure out the true issue.  My gut says this is a quality control snafu that arose from a similar production time line.  Its a shame, I still love the unit , but sadly I got burned twice. If its any consolation, having that balance out of circuit should theoretically result in a more "direct" and "pure" signal?  And let me say. I am a Parasound guy. I have the A21 amp, a PHP-850 pre(my favorite BTW), and a P3 Halo pre. I have been met with nothing but absolute class and empathy when I have written the company. RS is a Class act at the top. Best of luck.
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