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Recapping amps: facts, myths, legends etc

I've been thinking of sending my amp off for a service, it sounds fine in operation and is perfectly quiet, there is a slight channel imbalance favouring the left channel but that is sorted with the balance control.

The issue that concerns me is the quite large amount of noise on first start up, regardless of volume knob position, there's quite a bit of crackling and popping for the first 10-15 seconds until what seems like something is settling, then it's perfectly quite throughout, the longer it's been switched off the worse it is.

Not being electronically minded (with amps at least, I mainly deal with large 3 phase appliances at work) I've no desire to look at it myself, I'll probably end up sending it to Sugden but I hope it's nothing detrimental to it's sound.
 
Lots of people seem to be weighing in with their opinions and speculation I can’t see the point of replying unless you can provide some real help to this thread.

Here are some facts, electronic capacitors don’t like heat, no matter who makes them, they dry out or leak causing the value to get lower. This causes ripple on the supply’s resulting in hum and making the amp to sound shouty.
Hotter the amp sooner it needs recaping, enclosed amps like naim with big caps seem to need doing sooner than most.

Pete
 
Pete MB&D said:
Hotter the amp sooner it needs recaping, enclosed amps like naim with big caps seem to need doing sooner than most.
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This is obviously true/fact but I’d argue Naim were their own thing as they suggest leaving kit on 24/7, which is frankly daft. Kit will obviously wear infinitely faster if it is on all of the time rather than being used for how many hours one actually listens to it! I also find it very interesting that say Sugden do not do full recaps as part of services even on 1960s amps (or they certainly didn’t 15 years or so ago when I visited the factory), they just fix what is wrong. I guess the thread question is impossible to answer as some stuff will burn through caps far faster than other stuff and some caps are crap to start with. Rob’s perspective of pulling full sets of perfectly measuring caps out of early-70s Japanese kit has to be balanced against certain Audiolab DACs failing in a couple of years. It makes the decision process so much harder. I guess really what I’m asking is what are the subjective signals, i.e. is there anything I should be looking at beyond visual cues such as bulges, leaks etc, or hum, thumps, crackles or higher than expected DC offset?
 
My 135 clones burnt through the contacts of the 16A mains swtiches when I used to swtiches them off at night, the surge when swtiching on anything is when most things fail, so some things left on 24/7 are more relyable, naim soak test involves mutiple on/off cycles.
My 135 morphed into hackernaps which are left on 24/7.

Most of the internet is on 24/7 so is your heating fridge router etc 24/7 running isn't nessacerly a bad thing.

The best way to find out if your amp needs servicing is to replace all the caps and see if it sounds better, not the cheapest way. The the other way is to listen to it, as I said if it sounds shouty i.e. powerfull but harsh then its time to service, because the performance drops of sloly its hard to notice the change, a fresh pair of ears or a second system can help to identify the changes.

Your car allways sounds and feels better after a service, you don't notice the dropoff but it happens.

I can't beleve the position of the caps in your onix, they are near two heat sources and should have a hard life and need regular replacemet but I guess it must run cool.

I think the Audioab stuff was underrated which will cause overheating and leaking.

Pete

Sorry about the spelling my spell check seems to be on strike this morning.
 
If it sounds good leave it alone!

If you really want peace of mind, I would suggest reading this and building the tester. This will allow you to test the caps ESR without removing them:

http://conradhoffman.com/capchecktut.htm

I also have one of these (or very similar) for quick and dirty measurements:
https://www.banggood.com/Transistor...R-resistance-Meter-p-919181.html?rmmds=search
I can't remember why but I concluded that the capacitor bridge is better for in circuit measurements and for big caps (low ESR values).
 
Pete MB&D said:
I can't beleve the position of the caps in your onix, they are near two heat sources and should have a hard life and need regular replacemet but I guess it must run cool.
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One heat source, the transformer doesn’t get even slightly warm! In fact I’ve never known a transformer in a solid state amp that does (tube amps are obviously a very different thing, the Leak mains transformer gets to about 40-45 degrees C!). Back when I had Naim kit my HiCap and 135s or 250 was only above room temp if being caned into inefficient speakers. The caps in the Onix are close to the output transistors, but it doesn’t get more than mildly warm as far as I can tell, i.e. just a few degrees above room temp. We are certainly not talking class A here. I left it powered all day yesterday and after a good session driving the inefficient 149s the case above the output transistors was barely warm, cooler than say a Quad 306 or 405 just sitting there doing nothing.
 
off the track slightly 'reel to reel the only caps ive replaced are motor caps with a higher voltage rating and the mains rfi cap. with a higher voltage rating use 1000V
 
Tony, with your Onix I wold say it is worth replacing the tantalum (yellow bead) caps on the phono stage, other than that I would leave it for now. Tantalum caps do not age well. It looks like the phono stage board is easy to remove.
 
When I landed my close to mint Akai 4000db for a couple of tenners at the local auction house I did a lot of googling about it and again the caps seem to have very long life in these decks. There are stories similar to Rob’s of folk recapping them and finding all the ones pulled out still to spec. The things that fail in this machine are some of the transistors which become noisy with time. It does have some hiss for sure, but I don’t mind as it sounds nice and tapey!
 
df_genius said:
Tony, with your Onix I wold say it is worth replacing the tantalum (yellow bead) caps on the phono stage, other than that I would leave it for now. Tantalum caps do not age well. It looks like the phono stage board is easy to remove.
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I’ve not tried the phono stage, but will consider that as it is well within my ability.
 
I have an Exposure X, had it recapped by the factory, after about twenty two years of being left constantly on, apart from going away on holidays. Never noticed much difference in sound quality. How does it stack up against your main amps? Could you live with it in your system?
 
Nigel said:
How does it stack up against your main amps? Could you live with it in your system?
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Not tried it in the main system (15” Monitor Golds are very rare and valuable so I only drive them with stuff I have 100% confidence in, e.g. my fully rebuilt and ultra safe Quad 303!). I’ve been running the Onix in the JR149 system as they are rebuilt with new Falcon units so are repairable and it is very, very good, just how I remember my first one from back in the mid-80s! I posted some comments on the long JR149 thread in the classic room yesterday as to how it stacks up against my fully rebuilt Leak Stereo 20, but to summarise it is in no way disgraced.
 
Nigel said:
I have an Exposure X, had it recapped by the factory, after about twenty two years of being left constantly on, apart from going away on holidays. Never noticed much difference in sound quality. How does it stack up against your main amps? Could you live with it in your system?
Click to expand...

After selling my Naim gear I ended up with an Expo Super XX. 15 years old and with unknown ebay provenance (obviously).

Enjoyed it so much I sent it for recapping(after 4 years of ownership), more for longevity than any issues with the sound.

Plugged it in and I sat gob-smacked (I really don't use this term lightly) at the improvement. I wasn't expecting much, if any, change to the sound.
Just tons more detail on the top-end and mid-range(precis) and much improved stereo depth and width - goes with the former I suppose.
 
Whenever I recap, I normally fit higher capacity or quality items than what was in there originally, as modern caps are much smaller than the ones available at time of manufacture. Tony - you should check the value and size of those BHCs - you will probably find higher quality and higher capacity modern equivalents in the same form factor nowadays - a lot of manufacturers were governed by the physical size of the cap to dictate the value.

The only thing I have like for like recapped was a recent Cambridge Audio CD3 - for the first time I replaced every electrolytic with same values, except for slightly increasing those used to decouple the 4x TDA1541As. I sounded great afterwards...truth be told it sounded great before :)

One other item - if you have sent your amp back to the factory to be recapped, note that SQ differences might not only be related the caps - I would fully expect a manufacturer to reset bias, and this can also have a major impact on SQ.

Richard
 
I'm a firm believer in preventive maintenance - and therefore a regular recap. Case in point I have a NAP 90 on the bench right now. It was working fine until it wasn't. Now I know it wasn't Naim's finest hour in terms of design but the reservoir caps were all shot - and leaking badly and corroding the coating on the MB to the point i is not repairable. Had it been done a few years ago that amp would most probably still be working today.

I also just recapped an XPS for someone - not a cheap piece of equipment. All rail voltages measured normal but i refused to power up its companion CDX2. The problem - 3 of the 6 reservoir caps had gone open so the power rails would all collapse under load. No downstream damage done but again 20 year old caps that Naim say should have been replaced at 12-15 years failed.

I know there are people out there and reading the above posts is witness that even Naim caps can last significantly longer but how do you predict which units will be effected and when?

Just two of the cases I have seen that lead me to believe in "prevention is better (and cheaper) than cure"
 
Again I'd argue Naim are atypical as the kit is left cooking 24/7 so it is obviously going to dry out in a fraction of the time of say Rob's vintage Pioneers. Its the same with tubes; there are plenty of Stereo 20s, Quad IIs around with some or all of their original Mullard or GEC valves as they were only turned on when in use. 24/7 use would have burnt through them in under a decade. I do understand caps are different as they have a non-use shelf life and a little use actually extends life (re-forming), but even so I'd expect normal kit (Quad, Pioneer or whatever) that people just turn on to listen to music for a few hours a week and then turn off again to last many multiples of the Naims. Same with vintage analogue synths etc, there are loads out there with some/many/all of their original caps. They certainly don't need replacing every ten years!
 
Precis of things I've posted before here several times...What absolutely kills electrolytic capacitors (such a main PSU caps) is temperature. This is the caps' internal temperature, which depends on ripple-current far more than just the temperature inside the amplifier case. And with large/low-impedance transformers, the ripple current can be 5-6 times the idle DC current drawn by the amplifer: dissipating a watt or so inside reservoir caps is entirely possible, even in low-bias amplifiers. It all adds-up

A typical modern electrolytic cap will have it's lifetime specced by the manufacturer at something like 2000hrs at 105degreesC. On paper just 3months at full load and temperature!

However the actual useful lifespan - usually specced by capacitor manufacturers as 'to the point where rated Equivalent Series Resistance' doubles - essentially follows the Arrhenius equation in being related to running temperature: with lifespan doubling for each 10degreeC drop below rated temp.

So at 40degC that same cap should last 64*2000 or about 14years in continuous use. Try that at 45degC and perhaps one can see why Naim's rule of thumb of replacing main PSU caps at 7-10 years is about right - it really is about the useful lifespan assuming for full ripple current, 24hrs a day, at around 45degC internal temp. This is basic physics - not some Salisbury scam. 7-10 year replacements for a low-bias amp run 24/7 is just prudent.

Stick that same cap inside, say, a Class A amp exposed to heavy ripple (due to the constant high idle bias) and so running at 60degC and it will only last , on average, 3years or so - but you'd never leave such a thing on24/7, maybe 4hrs a day of use and suddenly the caps again might well last 10-12years or more. Equally, a low-bias amp used 4hrs a day might well be fine at 20-30years plus, if the cap seals have held and not lost electrolyte. Use a newer cap rated 3000hrs at 105egC instead and the goal moves back nearly 50% pro-rata; cheap or free when you are replacing the parts anyway.

(For my own amps I started with reservoir caps rated 60000hrs at 105degC - and film for everything else; so >40yrs left, really...even if left on 24/7.)
 
Looks a nice one that Tony. Caps are datestamped 1995 so that's your vintage. I've looked at a few oa21s for people on here over the years and the main fault has been the input switching relay under the phono board going. Easy enough to replace. Look after the ribbon selector switch as they are notoriously unobtanium. May be worth emailing Tony Brady at exposure for his thoughts. He may well just say leave well alone unless something breaks.
 
That is very interesting. I knew it was a very late one as it has a gold logo and the same type of speaker terminals as the OA401 & 601 power amps, but I thought Onix were long gone by ‘95!
 
martin clark said:
....Stick that same cap inside, say, a Class A amp exposed to heavy ripple (due to the constant high idle bias) and so running at 60degC and it will only last , on average, 3years or so - but you'd never leave such a thing on24/7, maybe 4hrs a day of use and suddenly the caps again might well last 10-12years or more. Equally, a low-bias amp used 4hrs a day might well be fine at 20-30years plus, if the cap seals have held and not lost electrolyte.....
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Class A amplifiers often have a fairly large bridge conduction angle, so the rms ripple current is not as large as you might expect.
Oversized transformers are the killer as the conduction pulse can get very short and very high. Naim like big transformers, hence the lifetime
 
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