How do aging amplifier capacitors affect sound?

[luckiestmanalive]

I've read in a few posts passing comments about people who have re-capped their old amplifiers. I'd like to know how aging capacitors affect the sound and how many years you might look at replacing them?

[JamesB]

I've almost always got good results by replacing old capacitors with new exotic, or well recommended capacitors (look for recommendations on diyaudio.com or audioasylum.com).

Changing capacitors changes the sound of the gear and sometimes you might end up with something you don't like and have to revert or try something different. Unfortunately there is no one size fits all. But looking for well recommended ones can make this less of a crap shoot. You can get a lot of good electrolytic types from Element-14 (was Farnell) quite cheaply and delivered next day (eg Panasonic FM/FC/ED, Rubycon ZA/ZL).

The other thing to look out for is how easy it is to get at the circuit boards to actually change the capacitors. I expect some amplifiers weren't made to be serviced easily, unfortunately.

[Owen Young]

This may be one for the qualified folks (Gary?) but I'll offer an opinion to start the debate debate...
As I understand, it depends on many variables, capacitors age owing to:
- How close to rated specs, eg. voltage & duration, how hard a life the cap has been subjected to.
- Age
- Temperature, ie heat.
- How many hours of use
- Lack of use ...caps sitting unused for years can be damaged by sudden application of voltage.
- Technology of caps has also improved over the years.

Generally, with amps, we tend to be most concerned with the electrolytic caps (PSU usually) which are typically run at near-continuous or DC voltage conditions. They contain liquid electrolyte which tends to dry out over time. The internal coatings and/or films can also become damaged over time with applied voltage & overall, performance thus deteriorates in various ways...loss of capacitance, voltage capability, increased 'leakage current'...

Not sure if you can characterise 'the sound of aging capacitors' but suffice to say that the amp performamnce will likely deteriorate.

How long? I've seen 50,000hrs mentioned (for PSU caps) but I would take that as gospel. As said, it depends...

[Gary.M]

I'd say if the gear is 20 years old it would be worth doing the electrolytics. If its a power amp and generates some heat, 15 years or less. As Owen says its time in operation + temperature primarily, but long term storage isn't good either. Film caps should be OK...

[Owen Young]

Oops typos above sorry, should read...
How long? I've seen 50,000hrs mentioned (for PSU caps) but I wouldn't take that as gospel. As said, it depends...

[Gary.M]

Of interest perhaps, but hard to relate to real usage I looked at the rated lifetime spec for the caps we are using in our Class A amp. 10,000uF 63V 105 deg C rated. Lifetime is 2000 hours at 105 deg C with the rated ripple current applied. Of course in normal usage they aren't at 105 deg C, and they operate below their rated ripple current... These are typical numbers as per manufacturers data sheets.

[luckiestmanalive]

Thanks, G and O.

[Owen Young]

I snipped this Derating Chart from a Panasonic site Tech sht for their alumin electrocaps:
7059
So, for Gary's example above, the caps could potentially have life >40,000hrs @ 60degC. Panasonic discuss other factors & recomms for obtaining best life. So, hard to give a firm figure on these things...
http://industrial.panasonic.com/www-ctlg/tech/tABA0000_WW.html

[Antipodes]

I find recapping tends to result in faster and tighter sound, with much improved macro-dynamics. Often there is a perception of reduced micro-dynamics and even a reduction in musical expression with new caps, but I put this down to the macro-dynamic changes.

[scotyd]

I had my 140 recapped and to my ears there was an improvement.It took a while after to (some would say change) improve but it did.Owning what i do there is much debate as to leaving on 24/7... as to turning off.I find leaving it on is my prefered sound as it is a constant whereas "reheating" the sound changes the longer it is on thus affecting life of the caps as per Owens chart.Perhaps to be a bit greener:D i should have bought something else but im green in otherways:p.
Cheers scotyd.

[C33]

Is there a good way to test capacitors? I know there a cap testers available at electronics stores and on some DMMs so if these are effective options some testing could avoid replacing healthy caps.

[Owen Young]

Hard to 'test' caps without some equipment (capacitance meter, ESR meter, measuring leakage current....). And then you need to interprete how/if such measurements relate to the circuit & therefore performance?

So, best to weigh up capacitor replacement from the POV of (i)age and/or (ii)different (or better) sonic quality parts.

[Gary.M]

Good one Owen. I looked for some derating info but couldn't find any.



I snipped this Derating Chart from a Panasonic site Tech sht for their alumin electrocaps: