I've never recapped an amp but I have recapped and modded a CD player before using a guide. Now I'd like to recap an old Rotel RA-314 but first I'm planning to get the cheapest working old amp I can find for practice. Once I'm confident with the process, I will move up to the Rotel.
The thing is I'm struggling with selecting replacement caps. Sure, I could just use Panasonic FC/FM/FR for everything, all with the original values. I'd like to take it just a tad bit further though. If anyone would be so kind, I have a few basic questions I would appreciate an answer to:
1. Is it okay to double the capacitance on all electrolytic caps in the PSU area or are there exceptions?
2. In all other areas of an amp: would it be better to use audio grade caps instead of the Panasonics to replace the decoupling and signal caps?
3. For which caps can I increase the values and for which caps should I definitely stick with the original values? (electrolytics only)
4. Any other parts beside the electrolytic capacitors that should be replaced after 30+ years?
Many thanks to whoever takes the time to provide me with answers!
The thing is I'm struggling with selecting replacement caps. Sure, I could just use Panasonic FC/FM/FR for everything, all with the original values. I'd like to take it just a tad bit further though. If anyone would be so kind, I have a few basic questions I would appreciate an answer to:
1. Is it okay to double the capacitance on all electrolytic caps in the PSU area or are there exceptions?
2. In all other areas of an amp: would it be better to use audio grade caps instead of the Panasonics to replace the decoupling and signal caps?
3. For which caps can I increase the values and for which caps should I definitely stick with the original values? (electrolytics only)
4. Any other parts beside the electrolytic capacitors that should be replaced after 30+ years?
Many thanks to whoever takes the time to provide me with answers!
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If you have successfully recapped a CD player, you a re ready to overhaul an amplifier.
First advice: forget Panasonic caps. They tend to lose capacitance and to leak DC current too soon. Go for Nichicon.
Do not increase capacitance, there is no need nor benefit to do that, however there are a few risks involved
Think about replacing trimpots, relays and opamps.
Use audio grade only along the audio circuits, use bipolar on signal path and use durable ones in logic circuits.
Good luck with your project.
First advice: forget Panasonic caps. They tend to lose capacitance and to leak DC current too soon. Go for Nichicon.
Do not increase capacitance, there is no need nor benefit to do that, however there are a few risks involved
Think about replacing trimpots, relays and opamps.
Use audio grade only along the audio circuits, use bipolar on signal path and use durable ones in logic circuits.
Good luck with your project.
Attachments
Thanks for the insight. The only issue I have with Nichicon caps is the short life rating (1000-2000h I believe compared to 5000 for the Panasonic FR). Of course it's much longer at lower temps but don't old amps (especially class A) get pretty hot? Might be okay for the signal caps though.
would increasing the capacitance for the very large caps at least be beneficial?
By signal caps, do you mean only the ones that are in series or the decoupling caps to ground as well (all caps that go to ground are decoupling caps, right)?
Finally, I don't know what a logic circuit is. How can I identify it in schematics?
would increasing the capacitance for the very large caps at least be beneficial?
By signal caps, do you mean only the ones that are in series or the decoupling caps to ground as well (all caps that go to ground are decoupling caps, right)?
Finally, I don't know what a logic circuit is. How can I identify it in schematics?
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Panasonic's life expectancy stated in datasheets is not reached in practice. Besides, the ratings are always stated for the maximum operating temperature.
Increasing capacitance in PSU puts additional strain on power transformer and also increase the PSU's output impedance. The bigger the cap, the bigger the inductance. Benefits from larger caps are subjective most of the time.
Signal caps are those on the signal paths. Audio grade capacitors should also be used in signal circuitry, such as in ground decoupling, filtering and so on.
By logical circuits I intend non-signal ones, such as servos, remote, command and so on.
Increasing capacitance in PSU puts additional strain on power transformer and also increase the PSU's output impedance. The bigger the cap, the bigger the inductance. Benefits from larger caps are subjective most of the time.
Signal caps are those on the signal paths. Audio grade capacitors should also be used in signal circuitry, such as in ground decoupling, filtering and so on.
By logical circuits I intend non-signal ones, such as servos, remote, command and so on.
Ah okay, still kinda worried though because class A amplifiers can get very hot, right? So I will look for caps that are rated at 105C, should be less of a worry then.
If I understand, logical circuits are digital which wouldn't apply to old amps from the 70s?
Seems pretty clear so far, thanks!
If I understand, logical circuits are digital which wouldn't apply to old amps from the 70s?
Seems pretty clear so far, thanks!
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Hello,
"Signal caps are those on the signal paths."
I know it's pretty dificult to understand, but every capacitors are in the signal path, even the reservoir capacitors.
Otherwise, they will be useless.
They are here to close the electric path for alternating current or to transmit audio signal from one stage to another one.
Except those which are in logic circuits.
"Signal caps are those on the signal paths."
I know it's pretty dificult to understand, but every capacitors are in the signal path, even the reservoir capacitors.
Otherwise, they will be useless.
They are here to close the electric path for alternating current or to transmit audio signal from one stage to another one.
Except those which are in logic circuits.
There are no "audio grade" capacitors. That's only marketing. As long as you use decent quality capacitors (which everything from Panasonic is) everything will be fine. There will be no difference in performance if you use standard capacitors or ones that are ultra-expensive (but still the same! Or worse!).
posts 2 and 3 show some of the argument we see when discussing electrolytic capacitors.
There is much in those two posts that is either exaggerated, or no evidence for the claims.
Normal commercial quality components generally meet specifications with a margin to spare.
It is rare to find a component from a reputable manufacturer that fails to meet specification.
Electrolytic capacitors fall into "component" category. They don't just fall over and die because of the name printed on the label.
There is much in those two posts that is either exaggerated, or no evidence for the claims.
Normal commercial quality components generally meet specifications with a margin to spare.
It is rare to find a component from a reputable manufacturer that fails to meet specification.
Electrolytic capacitors fall into "component" category. They don't just fall over and die because of the name printed on the label.
Audio grade capacitors are better damped against mechanical resonance and also exhibit less signal distortion by virtue of different chemistry and materials used. Both will bring the benefit of improved sound. Beside manufacturers' claims, there are measurements which prove so all over the internet. Brand which I recommended actually has very accessible prices for their audio ranges.
I also reiterate my own and other people's empyrical findings on rather quick deterioration of Panasonic specs. If lacking own experience, ask TV engineers and service technicians.
I also reiterate my own and other people's empyrical findings on rather quick deterioration of Panasonic specs. If lacking own experience, ask TV engineers and service technicians.
"bigger cap, the higher the inductance"
I think that has to do with fysical size, I replaced two 40+ year old 4700uF's with two 15000uF's that are 2/3 size of the 4700's, they are chasis mounted, this was easiest. (replaced bridge rectifier because I felt was a bit low ampères for bigger capacitors, but might be wrong entirely)
I think that has to do with fysical size, I replaced two 40+ year old 4700uF's with two 15000uF's that are 2/3 size of the 4700's, they are chasis mounted, this was easiest. (replaced bridge rectifier because I felt was a bit low ampères for bigger capacitors, but might be wrong entirely)
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Both Panasonic and Nichicon make 10000 hour service life caps, and 500 hour service life caps. You get the service life you pay for. I'm not going to download the datasheet on the caps you quoted, I'll leave it to you to do that. I've been buying Panasonic ECOS (3000 hour 85 deg C) caps and better, also nichicon and rubicon long life caps. United Chemicon the ripple factor at quoted "end of service life" was higher than the first three brands test to, so on that line at least I feel they have been fudging the numbers to look good. Also United Chemicon has come in sourced from a country famous for lying on QC paperwork for baby formula, concrete in schools and bridges, and meat sold to a fast food restaurant. The first three the parts have come in from other eastern countries less often in the news for disasters and uncompensated evictions.
I have not bought any "audio grade" caps, but in all cases, the long life industrial grade electrolytic caps I have been buying have achieved design wattage in power amps or made the organs sound better than tired old 1967 caps. I've installed over 200 new e-caps in the last three years.
I agree with pots and relay contacts being problems. I have not replaced tone controls since I don't use them much, but volume pots have needed replacement in all the units that used them.
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