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Aging amplifiers


mbain
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Can anyone suggest a " maintenance" schedule for hi-end amplifiers as they age. I own a pair of Mark Levinson 33H monobloc amps that are approximately 15 years old with low hours for their chronological age. I am concerned with aging capacitors as well as other electronic internal parts. What does capacitor failure sound like? How does the failure of other elements effect sound?

mbain

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Those amps are extremely well made. Unless you keep them in an unusual environment, they're probably still close to new condition. But if you're unsure and want piece of mind, you should speak to a really good repair shop. If you don't have anyone local, try Audio Classics in upstate NY. Its a very reputable place and is considered to be one of the best shops in the country.

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Can anyone suggest a " maintenance" schedule for hi-end amplifiers as they age. I own a pair of Mark Levinson 33H monobloc amps that are approximately 15 years old with low hours for their chronological age. I am concerned with aging capacitors as well as other electronic internal parts. What does capacitor failure sound like? How does the failure of other elements effect sound?

 

Capacitor failure can take a number of symptoms. The most common is probably increased power supply hum, but large power supply caps can catastrophically fail by shorting out as well. If that happens, you'll not need a list of symptoms to know it has happened! Now, I don't suppose that the ML has any interstage coupling caps in the signal path, but it might have other caps for bypass, etc., and if these fail, the most noticeable result will be a profound change in frequency response. Leaky coupling caps will result in loss of bass, and leaky bypass caps usually cause a big loss of high frequencies.

 

Low hours don't matter, because one is more likely to see the caps in unused equipment go bad than those used regularly. OTOH, modern caps (those made since the early 70's) have about a 25 year useful life, so I wouldn't worry about caps until you notice a change in performance. You should have a few more years before even contemplating a problem.

George

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As the large value filter capacitors age, there will be a slow degradation that you may not be aware of. The hum levels may increase as their value decreases, followed by harshness as they age, then in some cases with FET output stages this may result in HF oscillation with possible output device failure. At 15 years, for peace of mind it may be worthwhile getting the large value electrolytic capacitors replaced, and with a bit of luck it will last another 15 years.

Several years ago a 100W/ Çhannel Mosfet power amplifier that I had built almost 30 years earlier, was recovered from a friend's garage and tested by a CSIRO scientist. The main electros had dried out in one channel, and it sounded quite harsh in that channel. There was also evidence of an overheating resistor in that channel due to some HF oscillation. The other channel where the electros hadn't dried out measured so well that I was asked if I had access to distortion measuring gear when constructing it.

The replacement of that resistor and the large filter capacitors in both channels would have restored it to normal operation.

Incidentally, a friend of mine loaned his Krell Preamp that hadn't been used for a while to an E.E. friend and it failed shortly after. It needed to have all the electrolytic capacitors replaced. Non electrolytic type capacitors rarely fail these days though, unlike in vintage radios etc.

Alex

 

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As the large value filter capacitors age, there will be a slow degradation that you may not be aware of. The hum levels may increase as their value decreases, followed by harshness as they age, then in some cases with FET output stages this may result in HF oscillation with possible output device failure. At 15 years, for peace of mind it may be worthwhile getting the large value electrolytic capacitors replaced, and with a bit of luck it will last another 15 years.

Several years ago a 100W/ Çhannel Mosfet power amplifier that I had built almost 30 years earlier, was recovered from a friend's garage and tested by a CSIRO scientist. The main electros had dried out in one channel, and it sounded quite harsh in that channel. There was also evidence of an overheating resistor in that channel due to some HF oscillation. The other channel where the electros hadn't dried out measured so well that I was asked if I had access to distortion measuring gear when constructing it.

The replacement of that resistor and the large filter capacitors in both channels would have restored it to normal operation.

Incidentally, a friend of mine loaned his Krell Preamp that hadn't been used for a while to an E.E. friend and it failed shortly after. It needed to have all the electrolytic capacitors replaced. Non electrolytic type capacitors rarely fail these days though, unlike in vintage radios etc.

Alex

 

Amen, Alex!

George

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Can anyone suggest a " maintenance" schedule for hi-end amplifiers as they age. I own a pair of Mark Levinson 33H monobloc amps that are approximately 15 years old with low hours for their chronological age. I am concerned with aging capacitors as well as other electronic internal parts. What does capacitor failure sound like? How does the failure of other elements effect sound?

 

You will hear hiss at first and eventually static, then intermittent drops and then silence once it fails in my experience.

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It can be expensive to service older ML equipment. I know someone who had his 20 or 20.5 mono amps and 26 pre amp serviced. But cost him a lot. The amps are now in new condition no scratches anywhere and all the electronic were cleaned and replaced when necessary. I'm not sure how much he spend but I guess you could buy a very nice new amp for the money he spend. He uses the ML amps to drive Kenrick 4350 speakers.

[br]

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It can be expensive to service older ML equipment. I know someone who had his 20 or 20.5 mono amps and 26 pre amp serviced. But cost him a lot. The amps are now in new condition no scratches anywhere and all the electronic were cleaned and replaced when necessary. I'm not sure how much he spend but I guess you could buy a very nice new amp for the money he spend. He uses the ML amps to drive Kenrick 4350 speakers.

 

That is depressing. Carver amps and sunfire amps can be serviced at a very reasonable cost. However I get it, ML equipment cost more to begin with so they gotcha.

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That is depressing. Carver amps and sunfire amps can be serviced at a very reasonable cost. However I get it, ML equipment cost more to begin with so they gotcha.

 

You make it sound like they put a gun to your head. People that buy 20k amps usually know what they are getting into. I'm pretty sure the parts that go into the OP's amps costs more than whatever goes into a carver or sunfire.

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That is depressing. Carver amps and sunfire amps can be serviced at a very reasonable cost. However I get it, ML equipment cost more to begin with so they gotcha.

 

One of the problems with high-end, low production equipment is that the parts "go away". Ever tried to find those multi-section electrolytic capacitors they used to use in tube equipment from the fifties, sixties, and seventies. I recently rebuilt the PS in a friend's Marantz 10B FM tuner (don't know why. FM, these days, sounds lousy. Better off streaming over Internet - with 192 KHz or better, I'll guarantee it will sound better that the compressed and limited broadcast signal!). Couldn't find the multi-section filter cap. I got it done, but now it has a hole in the chassis where the "can" cap used to be, and the underside is littered with individual modern equivalent values stuck in every spare nook and cranny! BTW, the stereo decoder in the 10B ain't so good! The tuner has excellent RF performance, but unfortunately, without extensive modification, the SCA filter multiplex decoder in the thing chirps like a canary!

George

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