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#1
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Damage output cap's by letting them drain?
Hi Group,
I still frequently use a very old Nikko Alpha II poweramp that has been my workhorse for over 20 years. It will be replaced soon. It's been getting a bit fussy in the last years where distortion is sometimes getting audible etc. The protection circuit has been bypassed for a very long time now without trouble so it is now possible to turn off the amp and let the cap's discharge as they play the input signal for a few seconds. This is not standard practice but sometimes I do it when I'm fidling with inputs or outputs and let it go thinking it can do no harm. Anyway, although this amp has slowly been getting raggedy, the other day I let the cap's dischange and when I turned on the amp 10 minutes later the sound was gritty and distorted and non-symmetric. It took about 15 minutes to snap to and I think it's not completely the same anymore although pretty close. Nothing "bad" happened to the amp during this; no shorts etc. Does draining the cap's like this hurt them or something else in there? Thanks, Wessel |
#2
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In all likelihood the caps would have been drained by bleeder resistors anyway. This is unlikely to have caused your problem. You've been skating close to the edge by disabling your protection circuit though. It's there for a reason. Mark Z. "Wessel Dirksen" wrote in message om... Hi Group, I still frequently use a very old Nikko Alpha II poweramp that has been my workhorse for over 20 years. It will be replaced soon. It's been getting a bit fussy in the last years where distortion is sometimes getting audible etc. The protection circuit has been bypassed for a very long time now without trouble so it is now possible to turn off the amp and let the cap's discharge as they play the input signal for a few seconds. This is not standard practice but sometimes I do it when I'm fidling with inputs or outputs and let it go thinking it can do no harm. Anyway, although this amp has slowly been getting raggedy, the other day I let the cap's dischange and when I turned on the amp 10 minutes later the sound was gritty and distorted and non-symmetric. It took about 15 minutes to snap to and I think it's not completely the same anymore although pretty close. Nothing "bad" happened to the amp during this; no shorts etc. Does draining the cap's like this hurt them or something else in there? Thanks, Wessel |
#3
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#6
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Laurence Payne wrote in message . ..
On 3 Oct 2004 13:27:18 -0700, (Wessel Dirksen) wrote: I still frequently use a very old Nikko Alpha II poweramp that has been my workhorse for over 20 years. It will be replaced soon. It's been getting a bit fussy in the last years where distortion is sometimes getting audible etc. The protection circuit has been bypassed for a very long time now without trouble so it is now possible to turn off the amp and let the cap's discharge as they play the input signal for a few seconds. This is not standard practice but sometimes I do it when I'm fidling with inputs or outputs and let it go thinking it can do no harm. Anyway, although this amp has slowly been getting raggedy, the other day I let the cap's dischange and when I turned on the amp 10 minutes later the sound was gritty and distorted and non-symmetric. It took about 15 minutes to snap to and I think it's not completely the same anymore although pretty close. Nothing "bad" happened to the amp during this; no shorts etc. Does draining the cap's like this hurt them or something else in there? Charge a cap, disconnect and walk away. How long before the charge disappears from leakage? No, you're doing no harm. I take it you disabled the protection for audiophile reasons, not because it was operating? It means when you DO have a wiring fault, it may be catastrophic. But if you really notice a difference and think the risk is worth it, I believe it's the sort of thing audiophiles sometimes do :-) After 20 years, I wouldn't be surprised if the electrolytics needed replacing. If it's a nice amp, why not try this instead of dumping it? This is a multiple response in one. Thanks for your input everyone. I got this amp 20 years ago because it was "broken"; the protection relays were faulty then. I temporarily bypassed them to test the theory and when I replaced them I found the sound to be not nearly as good, so yeah, for audiophile reasons they're bypassed now since 20 years and I must be careful with it but there's never been an accident so far. (a few near accidents) OK good to know that this is not per se bad practice, so its something else. Even though I will replace this amp, I really want to ressurect it for another system because it's really quite cool. 2 huge input trafo's etc. I would like to find either an amp guru in the area (Netherlands/Belgium these days)or do some value for value replacing of parts inside. Which parts are best to "upgrade" to beter quality if I do this? Thanks again, Wessel |
#7
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#8
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Laurence Payne wrote in message . ..
On 4 Oct 2004 02:04:43 -0700, (Wessel Dirksen) wrote: Even though I will replace this amp, I really want to ressurect it for another system because it's really quite cool. 2 huge input trafo's etc. I would like to find either an amp guru in the area (Netherlands/Belgium these days)or do some value for value replacing of parts inside. Which parts are best to "upgrade" to beter quality if I do this? Just replace the electrolytic capacitors. You need components of the correct value and of a size that fits in the available space. No need to pay double for "audiophile" hype. Thanks Laurence, so I would ideally replace the eletrolytics probably with metalized film caps then I guess, or is this the expensive hype you are referring to. Does this mean that resistors and semi-conductors don't get old and/or are not worth replacing with "beter" types? Can the big output transistors be blindly part for part replaced with higher performing substitutes. They are NEC 2SB600 + 2SD555 as a pair per channel. |
#9
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The B600 and D555 transistors were rated at 200W each. You'd be hard pressed
to find a modern equivalent which would surpass them AND be well matched and reliable. Transistors are often counterfeited these days, and instead of matched NEC product you'd have to hope that the ONSEMI devices you get from a distributor are up to par. Mark Z. "Wessel Dirksen" wrote in message om... Laurence Payne wrote in message . .. On 4 Oct 2004 02:04:43 -0700, (Wessel Dirksen) wrote: Even though I will replace this amp, I really want to ressurect it for another system because it's really quite cool. 2 huge input trafo's etc. I would like to find either an amp guru in the area (Netherlands/Belgium these days)or do some value for value replacing of parts inside. Which parts are best to "upgrade" to beter quality if I do this? Just replace the electrolytic capacitors. You need components of the correct value and of a size that fits in the available space. No need to pay double for "audiophile" hype. Thanks Laurence, so I would ideally replace the eletrolytics probably with metalized film caps then I guess, or is this the expensive hype you are referring to. Does this mean that resistors and semi-conductors don't get old and/or are not worth replacing with "beter" types? Can the big output transistors be blindly part for part replaced with higher performing substitutes. They are NEC 2SB600 + 2SD555 as a pair per channel. |
#10
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Hi Guys,
I'm gonna resurrect this one with the following last request. I'm hoping those in the know will comment on the following strategies that I think are sound in replacing parts in my amp (assume value for value): 1 Cap's which bridge the output of a DC power source as a current buffer can be beefed up (increased capacitance)as far you want to go without getting rediculous. 2 All cap's + resistors in DC power supply path can be of lower quality 3 All cap's + resistors in the signal path, especially in series, should be of highest possible quality without getting rediculous. Which is better polypropelene or tautalium (spelling?) 4 Semi-conductors are less necessary to replace and cannot be appreciably upgraded without design modifications. Exception might be the "speed" of diodes in the rectifier circuit? (so I have read) Thanks, Wessel |
#11
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Wessel Dirksen wrote: Hi Guys, I'm gonna resurrect this one with the following last request. I'm hoping those in the know will comment on the following strategies that I think are sound in replacing parts in my amp (assume value for value): 1 Cap's which bridge the output of a DC power source as a current buffer can be beefed up (increased capacitance)as far you want to go without getting rediculous. They are 'storage/reservoir caps' not current buffers. Increasing them stupidly could possibly cause some damage to the recifiers if they were marginally sized. 2 All cap's + resistors in DC power supply path can be of lower quality Lower quality than the signal path ? Depends what you call 'quality'. Don't expect them to influence sound quality however. 3 All cap's + resistors in the signal path, especially in series, should be of highest possible quality without getting rediculous. Well... don't use **** for sure. Today's 'commercial quality' components are surprisingly good for the most part. Which is better polypropelene or tautalium (spelling?) There is no *better* - it depends on the application. Some of the esoteric audiophool clowns get all worked up over capacitor dielectrics. Reality is that most ( read all in practice excepting really bad design examples ) imperfections in an amplifer are due to the 'active circuitry' - not the passive components. 4 Semi-conductors are less necessary to replace and cannot be appreciably upgraded without design modifications. What improvement would you expect to see by replacing the designed in transistor with a different one ? Some op-amp designs can be improved by use of more esoteric ( read expensive ) types though. Exception might be the "speed" of diodes in the rectifier circuit? (so I have read) Yet another myth that I hadn't yet heard. Graham |
#12
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Wessel Dirksen wrote:
Laurence Payne wrote in message . .. Just replace the electrolytic capacitors. You need components of the correct value and of a size that fits in the available space. No need to pay double for "audiophile" hype. Thanks Laurence, so I would ideally replace the eletrolytics probably with metalized film caps then I guess, NO. Just replace them with new equivalents. You won't find metallised film in the large values you need - nor do you need metallised film for power supply caps. Does this mean that resistors and semi-conductors don't get old and/or are not worth replacing with "beter" types? Yes. Can the big output transistors be blindly part for part replaced with higher performing substitutes. They are NEC 2SB600 + 2SD555 as a pair per channel. Don't mess about. You'll have to re-adjust the output stage if you mess with those devices and likely do damage if you don't know what you're doing ( which seems to be the case ). Graham |
#13
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In , on 10/08/04
at 03:50 PM, (Wessel Dirksen) said: Hi Guys, I'm gonna resurrect this one with the following last request. I'm hoping those in the know will comment on the following strategies that I think are sound in replacing parts in my amp (assume value for value): 1 Cap's which bridge the output of a DC power source as a current buffer can be beefed up (increased capacitance)as far you want to go without getting rediculous. Beyond a certain point, you'll start blowing up the power supply diodes. 2 All cap's + resistors in DC power supply path can be of lower quality Different properties are important in power supply areas, than in the signal path. For example, installing premium low drift or tight tolerance parts in the power supply would probably be wasted money. Installing cheaper diodes as the main rectifier after you've beefed-up the capacitors as above, could easily result in diode failure (after a while). 3 All cap's + resistors in the signal path, especially in series, should be of highest possible quality without getting rediculous. Which is better polypropelene or tautalium (spelling?) If you are looking for physically small, tantalum is the choice. In an AC application, tantalum is a poor choice. For some reason, I see a lot less polypropylene failures then tantalum failures. 4 Semi-conductors are less necessary to replace and cannot be appreciably upgraded without design modifications. Exception might be the "speed" of diodes in the rectifier circuit? (so I have read) If they are too fast you may notice more power supply related noise in the unit. --- Years ago I had a fellow work in my service department who had worked for an amplifier manufacturer. He had lots of stories about "improvements". This particular brand was the darling of the "mod squad" (not to be confused with the company of similar name). The manufacturer's service department had a steady stream of units come in for major service to repair the damage done by tinkerers who thought they new more than the designer. Yes, it was possible to improve the sound of the unit, but the modifications often ruined the stability of the unit. An unstable unit is prone to quirky, unpleasant behavior at seemingly random times. ----------------------------------------------------------- spam: wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15 13 (Barry Mann) [sorry about the puzzle, spammers are ruining my mailbox] ----------------------------------------------------------- |
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