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THRESHOLD CAS-2 poweramp.
THRESHOLD CAS-2 poweramp.
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Old 8th March 2012, 09:36 PM   #21
Malotron is offline Malotron  United States
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Quote:
Originally Posted by shriekback View Post
Hi everyone,

So I have a near perfect CAS2. I have changed all the caps out, including the main PS caps, and it sounds brilliant and has worked without a hitch for a couple of years. Unfortunately, however, just recently the right channel of the level meter has stopped working properly with all the LEDs lit up. The left channel, and the amplifier itself, are still working properly.

Would anyone here have any tips as to what part has gone bad? Is it an integrated chip of some kind or a discrete part? If the former, might it or some equivalent still be made?


It's unlikely to be one of the LM339's if the left channel display is working - best bet is to compare your healthy left signal channel input network with the right. The .47uF zit red tantalums would be the first caps to go - ... once you take the face-plate off

-Mal
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Last edited by Malotron; 8th March 2012 at 09:39 PM.
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Old 9th March 2012, 05:14 PM   #22
Nelson Pass is offline Nelson Pass  United States
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THRESHOLD CAS-2 poweramp.
Check the voltage across those A42's. They are being used as zener
references, and might not be developing the voltage you want.



Nevermind, that would affect both channels.

One of the 339's on that side might be bad, injecting current into
the node the - inputs of each 339 have in common. Try shorting that
node to ground.

Last edited by Nelson Pass; 9th March 2012 at 05:17 PM.
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Old 1st August 2012, 10:48 AM   #23
shriekback is offline shriekback  United States
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Thanks Mal and Nelson for the help! I'll start with your suggestions and see if I can't get the amp back into proper fit.
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Old 27th February 2017, 09:18 AM   #24
shriekback is offline shriekback  United States
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Having solved the problem with the level meter with help here, a Beethoven string quartet was interrupted yesterday when the music in the left channel was suddenly replaced with a loud buzzing sound.

Switching inputs and outputs has isolated the problem in my CAS-2. My first suspicion was that a transistor had gone bad, inasmuch as they are, so far as I know, all original. A pal with a background in electronics, however, suggested that would normally cause fuses to blow (none have). Further, he thought the buzzing sounded like a 60-cycle hum which suggested to him a problem in filtering power supply noise out of the amplified signal.

Any suggestions here as to what might be the likely culprit?
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Old 27th February 2017, 09:33 AM   #25
Zen Mod is offline Zen Mod  Serbia
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THRESHOLD CAS-2 poweramp.
amp is old

what it needs is thorough examination by someone with proper expertise

not much luck with crystal ball
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Old 28th February 2017, 12:10 AM   #26
Zen Mod is offline Zen Mod  Serbia
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THRESHOLD CAS-2 poweramp.
even better

now I'm not gonna even pull da cover from my crystal ball
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Old 28th February 2017, 12:30 AM   #27
2 picoDumbs is offline 2 picoDumbs  Australia
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If electroytics are old replace them.
Just good practice.
Then take it from there, eliminate the obvious causes first, they're a timebomb, makes sense to replace them.
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Old 28th February 2017, 03:42 AM   #28
shriekback is offline shriekback  United States
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Thanks 2 picoDumbs! All the electrolytic caps were replaced 6-7 years ago when I first acquired the amp. That would have been my first suspicion otherwise.

I suppose one of them could have gone bad in that time, however, and might still be worth checking.
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Old 28th February 2017, 12:25 PM   #29
JamesBrennan4 is offline JamesBrennan4  United States
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I was going to suggest you check power supply rectifiers (diodes) for one being open, but after you amazing attack on ZM, I am not going to help.
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Old 28th February 2017, 05:08 PM   #30
Pano is offline Pano  United States
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THRESHOLD CAS-2 poweramp.
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