Capacitor replacement on my Linn equipment?

My Linn Kairn Pro pre-amp is approximately 20 years old now, similarly my Klout, although a very late one is now about 15 years old.

At what point should I consider giving them a re-fresh/service with new electrolytic capacitors?

The forums seem to be full of people raving about replacing the big electrolytics in their older Naim gear but you hardly ever read about the same with Linn.

I purchased both units second hand so I've no idea how much use they have had.

Both units sound *fine* to me but I haven't heard any other Kairns or Klouts so it's impossible to know if they could be better still.

 

If it still sounds good to you, might as well leave it be. But I would expect at 20yrs+ replacement is worthwhile. I keep meaning to pop up a short page on acoustica about this overall, so here's a rough draft of the core content:

Three things matter to the lifespan of electrolytic capacitors: ripple current, time, and temperature.

The ripple current is the big one - if an amplifier runs heavily into Class A and near-maximum power dissipation all the time, this means maximum internal heating in the reservoir caps (thanks to Iripple^2*esr) and so the shortest life. But for light loads like preamps and cd players where ripple currents are small, c.1-200mA roughly, this is not usually a guiding issue, becasue light currents do not drive up the caps internal temperature wildly.

Anyway, you'll typically find many new electrolytic caps are rated for 2,000 hours at 85 degrees Celcius or thereabouts - check their datasheets. You can often find 105degC rated vesions, too, and it is worth choosing these if they will fit as you'll see.

Electrolytic capacitor life basically follows the Arrhenius equation, where a change of 10degC roughly doubles or halves the rate of reaction. So while a 2-or-3000hr rating is usual for capacitors at full rated temp (to the point where ESR doubles from 'new' value), the reality is rather better at lower (internal) temperatures. Suppose your cap runs at about 35degC inside a well-ventilated case, or a lightly loaded piece of equipment (preamp/cd player):

Based on a rated life of 2000hrs at 85deg C that suggests a useful life around (2^[85-35/10])*2000hrs at 35degC = 2^5*2000 = 7.2yrs.

- Now you can see why Naim recommend service at 7yr intervals, based on 24/7/365 use. It's spot-on for prudent replacement.

Now, you'll find that caps rated at >>2000hrs at 105degC are now available at a very small premium. This might place high-quality reservoir cap replacements into the 'fit-and forget' category , with a realistic 25yr+ life at moderate ambient temps. (I like the Evox-Rifa PEH169 and PEH200 series for such things. They sound good, too. There are others of course.)

Note a capacitor manufacturer's rating is to a given criterion e.g. typically, to doubling of ESR. Which may have little or no audible effect in our uses! - depending on a given amplifier's sensitivity to component values. A given or predicted lifespan certainly does *not* mean the wheels suddenly fall off! But - to pick an instance - for Naim perhaps it does make very good sense since their classic amplifier design has a slightly lower PSRR than some other designs. A bunch of caps in a preamp, which see no significant riuple current and run at constant tempeature might easily and usefully last 2-3x as long without notable degradation. All a matter of design choices and trade-offs.

 

Sorry to hear about your knackered PSU Tenson, switch mode PSU's seem to be harder on capacitors what I've read.

Martin, thanks for the excellent post. Most of it goes over my head but I think I get the gist.

The Kairn is the older unit at about 20 years old but being a pre-amp I assume the capacitors aren't so heavily loaded. The Kairn also runs cool and never feels significantly above ambient temperature.

The Klout is younger at about 15 years old but I assume that being a power-amp the capacitors are much more highly loaded than the Kairn. The Klout also runs pretty warm, certainly not hot but always warm to the touch. When I got it I was surprised that it runs noticeably warmer than the LK140 despite the whole case effectively being one giant extruded heatsink.

All things considered my best guess is that it is probably worth doing the Klout first despite it being the younger of the two units.

I've been doing a bit of reading around on other forums and it seems that the small electrolytics are typically the first thing to fail on a Klout. From what I've read the big filter caps seem to hold up pretty well. Having said that if I've gone to the trouble of dismantling the unit already I'd be inclined to replace them too, if only for peace of mind.

 

"Having said that if I've gone to the trouble of dismantling the unit already I'd be inclined to replace them too, if only for peace of mind."

So true. I once serviced a DPA 200 power amp, and that was very much along these lines - by the time I'd go the damn thing apart, I did it all over just to never have to fault -chase the damn thing again...


Simon - yes SMPS are hateful devices. Owing to the high current ripple/RF switch rates you need the lowest esr caps you can arrange on the output side possible. But then you find, sometimes, not too low or they won't start-up...grrr. Try something rated 105degC min, or 130degC, and low-esr... once you get the thing working I've got away with usually adding-on some less-extreme regular electrolytics on the output for bulk reservoir use.

Input reservoir caps must be 450vdc rated min, and preferably high temp rated, too.

Theoretically these things could be great, practically.... just horrible imho.

 

Excellent post Martin. Definitely be good to see that expanded into an article.

On cap characteristic changes over time, much depends on where the cap sits in the circuit. An already way over specified electrolytic simply acting as a circuit coupler with very low dc across it can drift wildly with no effect on circuit performance. In high impedance applications as is typical for coupling, drifting capacitance and ESR matter little if at all.
Different matter in a PSU of course.

Manufacturers will often spec a cap to the nearest 'popular' value because those caps are very inexpensive to bulk buy. So if a circuit demands a 1uf coupling cap to meet a target response limit, you'll often see 10, 47 or 100uf used because the manufacturer has high stocks, or they are cheaper to buy.

Caps can have lots of non-critical characteristics in many circuit positions.

 

I just spent £150 on capacitors for the Klout.

Yikes!!

 

The £25 at Farnell wasn't too bad. It was the £130 at Hi Fi Collective that stung!

Basically I'm getting all of the smaller capacitors from Farnell but for the big filter caps I wanted nothing but the best. I'm not going to do this twice.

In the end I opted for Mundorf M-Lytic AG. They are about £16 each and I needed 8 of them!

I looked at the Evox Rifa caps which Martin suggested but they don't come in the right dimensions/specs for my Klout. Actually they are about the same price as the Mundorfs.

 

Guess what I did this afternoon...



Stunning build quality!

 

Rob, I'll pull it together soon - spent an hour or two this weekend digging-over some interesting graphs from some of the industry standards...

Spot-on.

I also re-read the datsheets for the Evox beercans I used in recapping the DPAs - 60,000hrs at 85degC, no that's not a typo! Even at a hot-bath 45degC that indicates a ~109year life indicated to replacement when left on 24/7 - so they weren't so expensive after all, may even see me out

 

This morning I got up to find that my television freeview box had died in the night.

I suspected some bad caps so I took the capacitors out of the PSU section and tested them. Most were OK but one small 22uF electrolytic was at half capacitance and had an ESR of 20 ohms.

I replaced the offending cap with one of the old ones which I just took out of the Klout and the Freeview box is now working perfectly.

A free fix on a freeview box can't be bad.

 

The Klout is now back together and sounding fantastic

Here are the details:

All of the small electrolytics came from Farnell along with the single large 10,000uF capacitor which is located on the separate PCB in the centre of the Klout. I did not alter any of the capacitance values but some of the voltage ratings of the new caps are higher than the originals. I tried to choose capacitors with the best possible lifetime specs, 105 deg C rated where possible.

I've had good experiences with Panasonic and Rubycon capacitors which did influence my choices.

Below is a list of what I chose including the Farnell order code:

Rubycon YXF 100uF 63v (x16) product code 114-4638
Rubycon YXF 220uF 16v (x4) 114-4615
Panasonic FM 68uF 35v (x4) 184-8393
Panasonic NGH 22uF 100v (x2) 969-3149
Panasonic TS-UP 10,000uF 63v 119-8724

The bid Panasonic is 35mm in diameter and the original is 30mm but don't worry it fits just fine.

For the eight large capacitors mounted vertically on the two PCB's either side of the Klout I decided to push the boat out. I re-mortgaged the house, sold a kidney and then ordered eight of these:



They are Mundorf M-Lytic AG 10,000uF 63v and they are 30mm in diameter x 50mm in height. This makes them slightly too tall to use in an upright position hence the single Panasonic mentioned above.

I got mine from the Hi Fi Collective, order code (MLGOAG-080)

The Mundorf caps have a self adhesive sticky pad which makes fitting them super easy. The sticky pad keeps them nice and tight against the PCB while you solder them in.



Lots of nice shiny new capacitors:



Everything back together.



I must say, the build quality on the Klout far exceeds anything else I have worked on. When tank manufacturers want to describe something as well built they probably say "Hey this thing is built like a Linn Klout".

BTW Rob is right about about cleaning the casework with WD40, it works wonders.

 

It's starting do dawn on my just how many electronic goods get chucked in the skip when quite probably they could be fixed at a negligible cost.

I threw my last freeview box away when is stopped working. This time I fixed it with a 30p part.

The Klout has been on all evening and is sounding superb. I just need to decide whether it's worth doing my Kairn pre-amp next. The power supplies in the Kairn shouldn't get the same sort of hammer as in a power amp (I would think). But then again it is 20 years old. Hmm..

 

Very nice job!

About the parts cost - well you've just bought an amp like the one you had and liked but is as-new condition - or better - sounds wonderful and good for another 20yrs or more. Bit of a bargain for £150, really...

 

That's very nicely built. Much more substantial than some of the LK units.

Lovely neat rebuild.

 

Thanks guys.

 

Replacing tant beads?

A couple of weeks ago I finally got around to taking my Kairn to bits with the intention of carrying out a capacitor replacement service. My Kairn is an early Kairn Pro (the prop has no phono stage) and has a conventional transformer power supply.

There are three big BHC electrolytic 'cans' with the following specifications:

2x BHC ALP10 series 33,000uF 30v 40mm diameter x 55mm height 5 pole termination

1x BHC 22,000uF 16v 30mm diameter x 40mm height 10mm lead pitch.


On the PCB there are number of small electrolytics. On my Kairn these were all pale blue coloured Rubycons:

12x 220uF 16v
16x 22uF 50v


For now I have only replaced the small electrolytics on the PCB. I used Rubycon ZLH 35v for the 220uF caps (Farnell order code 8126690) and Panasonic NHG for the 22uF 50v (Farnell 9692932).

Replacing the small electrolytics gave a subtle but worthwhile improvement to the sound. Definitely worthwhile given the very modest cost of the replacements.

On the PCB there are also eight small tantalum beads which I have left untouched:
4x 2u2 (2.2uF?)16v
and 4x 22uF 10v

It seems to be very popular amongst Naim enthusiasts to replace tantalum capacitors during a service. However I was under the impression that 'dry' tantalum capacitors did not have a finite service life like electrolytics do so why bother replacing them? Am I missing something?