why do capacitors fail/decay?

Now I think that those who might know this could be hanging out on DIY, but the answers are of more general interest.

What is it that causes components in amplifiers to fail, especially capacitors? Is it age, use, misuse? Does it make any difference if amps are kept on, or is it the surge from cold that causes wear?

Does all this limit the value of older kit?

Is there any sense in trying to get parts of older amps looked at?

Would appreciate some explanations.

(btw, I've never had the lid off and would not know where to start in recognising, let alone replacing a capacitors.)

 

Essentially the failure rate for kit looks like a bath tub. High failure at first, due to many thing, but mainly bad quality control at manufacturer. If kit gets through this then it can go on for years. Except then age causes components to fail.

A capacitor is essentially 2 plates separated by an insulator. When the insulator dries out, due to heat, obviously the capacitor breaks down.

A resistor is a coiled wire surrounded by an insulator, and again this dries out and breaks down.

So this does limit the value of second hand kit. Especially SS kit where the transistors used may not be available any more (these blow due to caps and resistors breaking down for instance).

However valve kit can usually be resurrected, as most valves are still available and the rest of the circuit is made up of caps and resistors which can be replaced. For instance I bought a non working Quad II valve amp for £50. Spent £10 in parts and sold it on eBay for £200. Easy when you know how.

 

despite your obvious limitations, as illustrated by your avatar, I think you have succeeded in giving me some enlightenment.

so, to follow-up, are there tell-tale signs of capacitor, and resistor, wear and tear - in solidstate amps?

It's now late 2004, and so amps made in 1999 are over 5 years old, those in 1994, 10 years old amps, etc. Accepting what you say about failure-at-new, what sort of life expectancy for capacitors, resistors and hence the unreplaceable transistors?

btw, as you may have gleaned from other posts, I'm pondering my next poweramp. My present poweramp (an integrated that can be used in poweramp mode) is the last, and maybe one of the best, of the AudioLabs, dating from 1998 (or should that be 1997): no probs there, its proving a verygood benchmark against which to test others.

But the others have ranged from last year's digital amp (PS Audio) right back to considering the Sugden P51 (30 years old!), and for the latter wear and tear might just be a consideration.

more intelligent comments pl

 

Usually, I think for a decent piece of equipment, they reckon on 10 yrs at moderate use. You could perhaps get double, possibly less.You can bet a 30 yr old piece will not be performing optimally and would benefit from being looked at.
Capacitors are the can and blob shaped things usually, dont' touch them after its been on, they hold volts, and can kill you if they are big enough.
REckon on at least 15-20 mins. to be safe, it depends on the design.
Tell tale signs, you can't really see any AFAIK, about simple ageing, obviously things attract dust and all that and get discoloured. Again, dents and cracking is a sure sign.
Its not rocket science, same as a house needing work.
Some get leaky, that is a sure sign, liquid oozing, but soundwise, you may not know until you do the work. Buzzes, hums, pops, crackles, all that.
Sometimes, aged components for some reason sound better, as the piece develops unique colourations through going out of tolerance.

 

Lee, I've re-read what I said in reply and realise that it was not as positive as it should have been for such a helpful reply. Its just that picture!! I don't know where to put my face!

LCD, another helpful reply. I feel I'm being gently educated ..

do you recommend spring cleaning of older equipment? Or is the black box best kept shut, and 'cleaning' restricted to external connectors?

Incidentally, does time taken to warm up indicate anything? There being two ways to read that: time before any sound; time before it sings.

 

With valve stuff, some have valves as rectifiers which apply the high volts, and take time to warm up, along with valves which have heaters which boil off electrons rather like a kettle or electric fire element, so they take time to 'work' 30 secs maybe.

As to improve/burn in, no idea. When brand new, they are like new cars and do improve, as to operating temp. perhaps, too, never really listened for it.

Not sure about your stuff, need specifics.

You can open it up, a bit of care needed a few times I have damaged things, due to not knowing what I was doing in the past, but if you are gentle ,you can use things like isopropyl alcohol or electrical degunker perhaps take advice on what to use.
A small brush, artists or toothbrush, gently can clean out areas.

 

Ditton, just for you a change of Avatar.

Unfortunately there are no hard and fast rules. It really is a case of suck it and see. Some say their kit doesn't sound good unless it has been on for a week

The amount of dirt inside an amp won't matter IMHO. I think one of the major factors is how hot is it inside, as it is this heat which dries things out.

Good luck with the search for a new power amp. I would recommend getting a digital amp, as I feel it has touches of the best of valve and SS. Ask WM, Penance etc for their opinions.

 

now that's the kind of surrealism I can enjoy ...

I'm wandering down D class way, having been impressed with the PS Audio, and now about to home demo the Flying Mole. TacT is surely just round the corner.

Ye Olde AudioLab 8000S is doing the driving just now, and it does do it, but hey, an itch is an itch ...

 

here is my secret tip, get a

http://www.qscaudio.com/products/amps/powerlight/powerlight.htm

or a crest or crown, to be totally different, pro audio is great quality at prices that will make hifi look silly, and look at the specs, hifi makers ought to be ashamed.

 

I have to agree with the QSC [never heard that exact model tho..] Data - though they are not as good value in the UK. This one is definitely the dogs nads:

http://www.soundslive.co.uk/moreinfo.asp?id=510

A pro amp used domestically should last for donkeys years. And these things are made to be servicable