Passive Crossover Capacitor Lifespan ?

[Eric Natural]

I read that often vintage amplifiers need capacitor replacement to return to spec. They need to be "re-capped".
Is this also true of caps inside the crossovers ? I've just replaced the tweeters with new ones from Kevro - for my 30yr old Monitor Audio Studio 6s and they sound just fine . . .
TIA

 

[Verig]

Voltages and operating temp are quite different inside a power amp than a passive speaker. If the caps are a bit off spec it doesn't make the sound necessarily worse, they may be a bit off spec to begin with. I haven't personally ever seen problems with speakers but then again oldest gear I have is not that old, usually just 10-20 years. Except TT is 45 years now. But interesting question.

 

[Pareto Pragmatic]

I read that often vintage amplifiers need capacitor replacement to return to spec. They need to be "re-capped".
Is this also true of caps inside the crossovers ? I've just replaced the tweeters with new ones from Kevro - for my 30yr old Monitor Audio Studio 6s and they sound just fine . . .
TIA

I can't speak to the lifespan of all caps of all types. But I can say that I had some 37 year old speakers that sounded just fine. Then better when I recapped them with very inexpensive capacitors . Everything was just a bit sharper in terms of focus.

They were in heavy use, but iirc electrolytic caps degrade over time whether in use or not, which is what was in them. For that type of cap, 20 years? 10 if you are super picky?

If you can solder, this is one of the easiest things you can DIY, at least I think so.

 

[wwenze]

otoh capacitors in speaker crossovers are subjected to huge current and voltage swings, but that's why they are usually film caps to begin with. Except for that one high-value one which unavoidably has to be electrolytic unless your speaker costs $1,000

Anyway I've seen both die. Film caps in crossover as well as power caps (non-SMPS). Leaky power caps can actually go undetected for long since all that does is reduced max output capacity (more clipping), more noise, maybe more distortion (impedance too high for feedback to cover, again related to max output power). Defective film caps also go undetected if the distortion / FR change is small

 

[Martinvb]

Until recently, I was quite sceptical about replacing cosmetically OK caps in older speakers. Then I replaced the caps in Goodmans Mezzo II speakers (1968), with no audible effect (A/B) whatsoever–even though the drivers of this 2-way unit were in excellent condition. Replacing all electrolytic caps in a set of 50 year old Kef 104's (supplied by Kef spin-off business Falcon Electronics) resulted in clear audible changes: more clarity, somewhat improved sound stage, etc. Changes were not that great, but for me still worth the investment because I re-appreciated the quality of these oldtimers.
So if you are really fond of your vintage speakers (which should be of good quality to begin with) you might benefit from a cap swap–that is, if you can find proper replacements for the old caps. If you want to go that route, be sure to treat one speaker first and critically compare it with the untreated speaker (speakers in approximately the same position, mono signal, high resolution music, A/B setup): when you evaluate the end result in two treated speakers you might not remember the sound quality of the original speakers. In that case, you may be biased toward noticing sound improvement (size of which correlates with financial investment, the effort it took to replace the caps, or both ).

 

[Eric Natural]

Thx guys. I guess I'm surprised that this age issue isn't a known thing - some do, some don't, you gotta test . . . is what I infer from the feedback above.
The sheer number of hits w/few replies to my OP also indicate a level of uncertainty about caps aging don't you think ? Usually, if something is known, one of the brilliant EEs who frequent this forum would chime in against any obvious bad information.

 

[Martinvb]

User @ctrl once posted a very interesting study about replacing crossover caps with ‘high end ‘ (or ‘audiophile grade’) ones. A very sobering study, indicating that in terms of measurable differences there is not much (if anything) to be gained by huge investments in such fancy components. Like you say, this is a topic in audio that would deserve a more critical approach by consumers, particularly those who are interested in vintage audio and who want ‘the original sound’ back.

Thread 'Audible difference in high-end capacitors? - ABX samples'
https://audiosciencereview.com/foru...nce-in-high-end-capacitors-abx-samples.48703/

 

[AnalogSteph]

Fundamentally, there aren't very many things that can turn crossover electrolytics into a writeoff:
1. Drying out, when the seals haven't been doing their job properly. Smaller parts are more sensitive, as you may imagine. Measure ESR and capacitance to find out.
2. The electrolyte chemistry turning acidic over time, which has it attack the crucial oxide layer so the latter will never be stable again. (I presume that's what's happening with the notorious '80s/'90s blue Philips axials.) Measure leakage current after a reforming attempt to find out.
It goes without saying that capacitor make, series, value, production time, individual part history and sheer luck all factor in, so predictions are going to be limited in scope.

Any well-preserved smooth foil bipolar electrolytics are good candidates for reforming, once in both directions obviously. Charge to rated DC voltage via 1 megohm or so, while turning up the voltage slowly at first and monitoring voltage drop over the resistor (i.e. effectively leakage current by way of Ohm's Law - basically any cap worth its salt should settle below 0.01 CV, possibly an order of magnitude lower). One of the better tools for doing this would be a classic oldschool capacitor leakage tester, as lab power supplies rarely go beyond 30 or 60 V DC and high-voltage DC sources up to at least 200 V DC are not exactly growing on trees (not to mention that they should be handled with due care). If push comes to shove, there's always the option of using an existing power amplifier with variable input and a rectifier diode (e.g. 1N4007)...

 

[Eric Natural]

thx Steph !
I do remain a bit sceptical of the need to replace my caps. Lots of vibration for sure but don't think that there's not a lot of heat generated inside the box to degrade the components is there ? Could you or someone identify what a bad crossover capacitor might sound like ?
I could certainly, as you suggest, take the speaks in to my tech(Blackie is excellent tho, I've successfully used him before) for maybe $150 in testing incl the $95 bench fee. I would if I were to perceive distortion or poor balance woof v tweet but that's not the case & I'm grateful. They do sound pretty good . . .
Cheers

 

[Ron Texas]

15 minutes.

 

[wwenze]

Use your phone or something to measure the tweeter and woofer of both speakers. If they have the same FR your xo caps are probably good.

 

[Wolf11Man]

With such an old speaker, changing the electrolitcs is simply something you do, not discuss. It is an investment of maybe 5-15$ so ask your self, how much are your speaker worth to you. If you put in some certified 1:1 exchange tweeter, a must do. They may have failed because of such a capacitor.
On the other hand, if you just got some cheapo tweeter that fit's the hole in the box and you "think" is about similar, forget about it.

 

[Pareto Pragmatic]

Could you or someone identify what a bad crossover capacitor might sound like ?

It will sound more distorted/noisy. How much more depends on how bad they are.

Kind of like a bad fuel injector in a car. If the flow to the engine (driver) is off, the engine will run rough. The more the flow is off, the rougher things will run.