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left channel on C1 preamplifier will partially drop out after playing a while


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I'm hoping someone can help me out here. 1 of the 4 C1 preamplifier's that I did the billD upgrade on is starting to show an issue after about 6 months of use. My left channel will lose about 50% of its amplification after the unit has been on and running for a little bit. The pots are clean and silent, to get the left channel back to 100% I have to restart the preamplifier with the power switch.  I thoroughly checked all the solder and everything looks completely fine, any ideas would be greatly appreciated.

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Intermittent failures can be very hard to pin down. The first step is to try an isolate the problem by simplifying the signal path. Disable the sub sonic filter, tone controls, and Sonic Holography. If the problem vanishes, add one back in. If it reappears, you have a better idea of where to look.

 

 

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Hello Pops Backflow, and welcome to thecarversite.com. We're glad you're hear. ;) There is a lot of information here, much technical know how, and a pretty good bunch of folks that are happy to help. 

 

I wish I could be of help, but I am no help under the hood. Others have already chimed in, and I hope they've pointed you in the right direction.


Once you get to Novice status, please consider uploading some pics of your gear in the Members Systems area. We all like pics of all kinds of audio gear.


In the meantime, kick your shoes off, turn up the music, and welcome aboard.

 

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I did try disabling everything to no avail. The op amps and brown dog adapter look good but I'll reflow the solder just to make sure. It's just so strange that the only way to get the channel back is to turn the preamp off and back on again. When I get to the bottom of it I will let you guys know in case somebody else has an issue like this. 

 

I will say that I checked almost every single parts values before installing them. I know that may seem crazy and a waste of time but I don't have the equipment or experience to track down a questionable part after the fact.

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If the problem occurs with the signal flow down to just the main line amp, then that is where I would look. If you have the opamps in sockets try swapping them around (if you have more than one) and see if the problem follows the opamps.

 

Having to cycle power makes it look like a problem in an active device which narrows it down to opamps or  the  JFETs in the muting circuit.

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Welcome.jpg.5ffd2eeecb7ee994d02dfedc1b9718b3.jpg

 

Welcome Pops!.  Yes, tracking an intermittent problem is a tough go.  A nice solid problem is so much easier - no matter what the subject.

 

I can't help much on the actual electronics, but here are some things that ,ay help narrow things down.  

 

  • Does the problem happen on headphones, or just main outs?
  • Does it happen with sh on or off.
  • What about with the tone in defeat vs on?
  • Is it on all inputs?

Try to divide and conquer.  These can help the tech's here guide you.

 

Can you swap op-amps with another of your C1's?  I totally understand if you don't want to do that, but it will tell you if there is an op-amp issie.

 

Beyond that, a definite big welcome to an obvious Carver addict.  Glad to have you here.

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Thank you for the great suggestion, swapping the op amps is a great idea. I'm just a hobbyist but I've been soldering every sense I built my 1st crystal radio with my dad 4th of July 1970. That's not to say that I do not have a bad solder connection but swapping the op amps as opposed to re-flowing seems like a better path for success.

On another note for those who are interested I've got over 4000 hours on Bob's 275 with a stock tubes. Every thousand hours I will swap in my reference tubes that are new and just broken in, I could not hear the difference when both sets of tubes were new from each other. So far neither I or my friends can detect any sonic degradation so far. Eventually I will move the 275 into the bedroom and put 350s out on the main system.

I've tried 1/2 a dozen top-of-the-line preamps and Bob's 40-year-old C1 is a match made in audio heaven for his latest bottle line up IMO.

 

Thanks again everyone for your suggestions I really do appreciate it. This was the 1st time in my life that I've ever posted anything and I'm glad it was here.

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Thanks for the info on the '275's - I know there are a number of folks here who have them, and many who are, well, drooling over them.  We do very much like to hear what others are experiencing with them.   ~^

 

I hope the suggestion helps, but do be careful - the last thing you want is to possibly damage the Op-Amps - they are a wee tad more pricey than a resistor.  ¬¬  If it were me doing it, it would be a fait accompli - they'd all be fried, but then I can't wield a soldering iron to save myself (my fingers are still healing from my last attempt).  :$

 

This group seems to be incredibly open to helping others, and a truly friendly lot.  I haven't been here very long, compared to many, and the responses to questions never fail to be there.  If you don't get an answer to one.  Bump it, people may just be unsure, but there are definitely folks here who can fix almost anything Carver or similar, and they are generous with their assistance.

 

Don't forget to relax and enjoy the music!  :D

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Fortunately for me I have a veriac and a high-quality powered de-soldering gun. I attempt to rebuild or repair dozens of components every year for the last 50 years and there is no way I'm going to use a hand pump or solder wick on something that has a 25% chance of bursting into flames when I'm done. I can use that time I've saved with the vacuum pump to fix something else that may burst into flames when I'm done with it. 

 

Before I left for work this morning I went ahead and switched the op amps and I found 2 questionable solder joints on a couple of resistors that I re-float as well. I plugged the C1 in and ran it on the test hi-fi while I was at work. So far so good! left channel has not lost any volume so far. Typically it would run for 20 to 60 minutes and then the problem would rear its head. I'm going to go ahead and let it run for another 24 hours just to make sure.

 

Because I re-flowed 2 solder joints that looked like they "may" have been questionable I'm not sure if swapping the op amps or the reflow solve the problem. If I was going to put some money on it at this point I would have to assume that it was the op amps because the solder joints were not necessarily bad they just weren't quite as perfect as the other solder joints.

 

I have got my fingers crossed "in spirit" again thanks for all the responses. 

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Good catch on those solder joints.  Odds are one was a bit iffy and as things warmed it would start causing trouble.

 

If it were an op-amp issue, it very likely would have come back.

 

Here's hoping you're in the clear and ready to let the music flow, instead of the solder!  :D~^

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