I am planning to replace the 8 x 6800uf 63V capacitors on my amp as they are 20yrs old.....
I am curious if brands of capacitors matter. The original ones are nichicon ones. But if I use brands like cornell dubilier, Kemet, united chemicon, will there be any significant difference in the audio?
I do understand mundorf is good but its very costly so I am looking for alternatives.
I am curious if brands of capacitors matter. The original ones are nichicon ones. But if I use brands like cornell dubilier, Kemet, united chemicon, will there be any significant difference in the audio?
I do understand mundorf is good but its very costly so I am looking for alternatives.
Probably the more important question is not so much brand, but does the "series" of capacitor matter. Each brand will have different series with differing specification making them more or less suitable for a particular purpose.
The datasheets are your friend. For Power supply caps ripple current handling will be one important parameter. Low ESR will be another, whether they are 105 deg or 85 deg and the estimated lifetime at those temps could be another factor you want to consider.
You will likely get the full gamut of responses here from it doesn't matter at all to brand X sounds infinitely better than Brand Y.
Tony.
The datasheets are your friend. For Power supply caps ripple current handling will be one important parameter. Low ESR will be another, whether they are 105 deg or 85 deg and the estimated lifetime at those temps could be another factor you want to consider.
You will likely get the full gamut of responses here from it doesn't matter at all to brand X sounds infinitely better than Brand Y.
Tony.
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Thanks for the reply. I am thinking of the Kemet ALC70, they are rated for 15,000hrs!! Wow!! Since the original ones are 85C, I guess using back 85C should be ok.
In the past 105 degrees celsius, low ESR and long life were combined in the "105" types but as we can see this is not the case anymore. The ALC70 seem a fine choice on paper. I take it your device is not becoming too warm as the old caps have lived for 20 years.
You very likely will be disappointed at first switch on. After some time (think 15 minutes) you will probably notice better bass.
Depending on the circuit you can replace the old 6800 µF for a higher value as you get more cap for the same size nowadays. This shouldn't be exaggerated but I guess 10,000 µF or even 12,000 µF will be about the same size as the old 6800 µF. A higher voltage rating is also possible and that certainly won't hurt. Many manufacturers choose tight ratings as lower rated caps are cheaper. So where 6800 µF 50V was used often a recent 10,000 µF 63V will fit. Measure the voltage on the caps just to know.
It is recommend to have a look at the also 20 year old rectifiers! When upping value of the caps this is a must anyway and it is advisable in any case considering the low cost and the way better properties recent diodes have.
Also check if the device has a 240V primary winding (if you live in a 230V area). When using newer diodes with lower Vf this might be a good thing to do. Mains voltage is often higher than expected too. It is surprising to see older equipment still being connected to the 220V primaries while a 230 or 240V possibility exists 🙂
You very likely will be disappointed at first switch on. After some time (think 15 minutes) you will probably notice better bass.
Depending on the circuit you can replace the old 6800 µF for a higher value as you get more cap for the same size nowadays. This shouldn't be exaggerated but I guess 10,000 µF or even 12,000 µF will be about the same size as the old 6800 µF. A higher voltage rating is also possible and that certainly won't hurt. Many manufacturers choose tight ratings as lower rated caps are cheaper. So where 6800 µF 50V was used often a recent 10,000 µF 63V will fit. Measure the voltage on the caps just to know.
It is recommend to have a look at the also 20 year old rectifiers! When upping value of the caps this is a must anyway and it is advisable in any case considering the low cost and the way better properties recent diodes have.
Also check if the device has a 240V primary winding (if you live in a 230V area). When using newer diodes with lower Vf this might be a good thing to do. Mains voltage is often higher than expected too. It is surprising to see older equipment still being connected to the 220V primaries while a 230 or 240V possibility exists 🙂
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Curious why would you say that. How are the rectifiers any different in aging compared to the transistors on board?
Or do you mean that raising the capacitance would place higher current demands on the rectifiers?
The rectifiers have switched large surge currents for years when the device was powered on. The transistors have not switched the surge currents through the filter caps. It would not be the first time old rectifiers would die when powered on with brand new low ESR caps. Please note that 20 years ago low ESR caps were not used often in power supplies for audio. Secondly new thus low ESR caps with larger values also pose even higher surge currents at power up. So in effect lower ESR and higher value can be a threat for old diodes.
This is not theory but things that happen a few times in practice and then one is a bit more cautious.
Newer diodes may have desirable features like lower Vf (Schottky), being faster, higher current rating or slow/fast recovery depending on the fashion of the moment 🙂 Not fashion but a true improvement are LT4320 based ideal rectifiers. I still struggle to see why they not always work in symmetric PSU's though. Have only used them in asymmetric PSU's with extremely satisfying results.
This is not theory but things that happen a few times in practice and then one is a bit more cautious.
Newer diodes may have desirable features like lower Vf (Schottky), being faster, higher current rating or slow/fast recovery depending on the fashion of the moment 🙂 Not fashion but a true improvement are LT4320 based ideal rectifiers. I still struggle to see why they not always work in symmetric PSU's though. Have only used them in asymmetric PSU's with extremely satisfying results.
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As large filter caps often were mounted in brackets one is often bound to that format. This automatically means one HAS to up the values as capacitor technology has improved over the years. This also counts for PCB mount snap in caps where a certain pinout is used that defined the values of 20 years ago but now may be the pinout of much larger values. Some are stubborn and use melt glue, selfadhesive band and extension wiring (ESL....) to mount same value caps but that is category ****ing around. A device should not be damaged when one places it a bit rough on the table so to speak.
For instance: when renovating/refurbishing seventies gear one will find that 25V electrolytic caps of that time have the size of the current 50 or 63V versions. So one can either up the voltage rating OR the value OR a bit of both (which is best IMO) but please don't take it into the extremes.
edit: I see things are not problematic when going symmetric with LT4320:
https://evotronix.eu/main/wp-content/uploads/2020/03/SalignyALL@2x.png
For instance: when renovating/refurbishing seventies gear one will find that 25V electrolytic caps of that time have the size of the current 50 or 63V versions. So one can either up the voltage rating OR the value OR a bit of both (which is best IMO) but please don't take it into the extremes.
edit: I see things are not problematic when going symmetric with LT4320:
https://evotronix.eu/main/wp-content/uploads/2020/03/SalignyALL@2x.png
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I get your concerns about low ESR caps.
About the 4320, it's very simple really: the lower and upper mosfets in the bridge are not treated equally by design. The lower ones turn on for half the cycle, while the upper ones are on only when the input AC voltage is greater than the capacitor output voltage. After all, mosfets are not diodes and they need to be told when to conduct and when not. The lower ones do not need the special treatment as their conduction is controlled by the upper ones. This alone makes it unfair to expect that a 4320 can be used as a direct replacement in a dual polarity supply.
And there is more. Notice that the bridge consists entirely of N-type mosfets, because they are better and cheaper for this application. This presents no problem with controlling the lower pair, but the top pair expects gate voltages in excess of the peak AC voltage in order to turn them on which the 4320 must also provide. Another source of asymmetry making it impossible for the 4320 to work with a negative voltage.
MOSFETs are one of the many weak points in my mind. Thanks for the clear explanation. One would think there would at least be 1 manufacturer integrating the whole shebang in 1 four pin package. Would make stuff way easier.
Btw it are not concerns but real life failing diodes that make me state this.
Btw it are not concerns but real life failing diodes that make me state this.
This also calls for an explanation 🙂
Sync rectification controllers exist to satisfy some industry need, not to serve our diy whims 😎
The AUIRS1170 is a lot more useful as it was primarily designed to cater for the charging systems of electric cars. Thus the high voltage abilities and also the ease to use it in both full wave and bridge topologies.
I believe our hobby will greatly benefit from all the research and new tech electric vehicles are bringing. Beginning from a huge choice of trench Mosfets, and sync controllers, to off the grid supplies using the latest battery and supercap tech and probably even ending with better grid delivered to our homes and wider availability of 3-phase power.
Thanks, I was not aware of the 4320.
Tell me more about the 4320.
The 4 MOSFET are of the same type, right ?
What MOSFET do you recommend ?
I presume it depends of needed PSU current and voltage, so please quote some usual cases.
Tell me more about the 4320.
The 4 MOSFET are of the same type, right ?
What MOSFET do you recommend ?
I presume it depends of needed PSU current and voltage, so please quote some usual cases.
Yes our hobby may benefit but the environment won't be better I fear. As a former green energy tech I have seen too much in this field to know it is just business. There is only 1 real solution to be green: that is to not use the energy at all. All other forms of energy saving are just ways to continue life as we know it.
Regarding 3 phase power.... development are more heading to the use of DC.....
@mchambin: there are various threads about LT4320 (PLEASE use complete part numbers as there is already enough confusion as it is)
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