Why do caps have to be replaced?

ricohman

ricohman

Adventure Rider
This is a total newb question, but why?
Are "caps" capacitors?
And do I need to replace these in the Mach One's or the STA2000 receiver?
Or if it's working just leave it alone? I notice that a lot of you replace these when obtaining a new (to you) piece of equipment.
Although I am a mechanic, I seem to have zero knowledge about electronics!
 
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Electrolytic capacitors have a shelf live, about 20 years, before the dialectric starts to break down, which changes the electrical characteristics of the component. So filter caps in power supplies and crossover caps in speakers that use electrolytic caps need to be replaced to bring them in spec.

In power supplies, its dangerous and damage to the rest of the unit can occur.

In speaker crossovers, the frequency that the circuit was designed for changes, and never for the better.
 
If you plan on using those speakers a lot (or as your main speakers) I would recap those for sure. Like specialidiot says, changing the intended crossover points can never be a good thing.

As for the 2000, it might be okay, but as many people have experienced, vintage capacitors DO eventually go, and when they do there could be some damage done to the unit.
 
Replacing Xover caps is a walk in the park.....compared to recapping an amp.
Unless you can do the work yourself.....expect to spend a couple of hundred for a tech to do it.

Steve
 
Thanks for the tips.
I would like to recap the mach ones first.
I need to search and find what parts I need so I can get it done.
The amp I may take to a shop and have it done.
 
The GOOD part is that modern electrolytic capacitors are very cheap compared to their cost several decades ago.
And modern ones are much smaller, so you can always easily fit them into tight spaces.
An annoying thing though is that you can't easily get axial types anymore (wires comming out of opposite ends of the barrel), so you have fudge things to fit in radial types.

Beware - there are a lot of *really crap* chinese caps out there; they will give you 6 months to a year of use before they fail. If you let someone else recap your stuff, be sure they put in reputable brands.
Vintage caps usually dry out gradually & slowly - they fail invisibly. Cheap modern junk caps usually burst & leak.
 
The concern about capacitors is real, but somewhat exaggerated.

Electrolytic capacitors do not age at the same rate, and film capacitors age very little.

High currents relative to internal wire size and proximity to other parts, usually power resistors and regulator transistors, are the main causes of electrolytic failure (along with the fact that some parts are simply very cheap and fail because they are poorly constructed and/or use inferior materials.)

* * * * *

A "basic recapping" on a receiver involves replacing the capacitors in the signal path, and the capacitors in the power supply that show signs of aging as measured with an ESR meter.

* * * * *

I prefer 105-degree capacitors from Xicon or Nichicon. Panasonics are also good. Mouser and Digi-Key are preferred sources.

* * * * *

Many folks will replace the main power supply electrolytics first. Generally these caps are less in need of replacing than the caps listed above.

* * * * *

As much as possible, try to keep to the original voltage and microfarad values. You will have people advise you to go up in voltage. Don't. Increasing microfarad values will change the frequency response, and will often lead to oscillations.

* * * * *

Look at how the original parts are mounted before you remove them. Do not rely on the "silkscreening" on the circuit boards -- this nomenclature is sometimes wrong!!! Remove and replace parts one by one. Do not pull all the caps at once, and then replace them en masse. This can lead to technical errors.

* * * * *
 
steerpike2 said:
The GOOD part is that modern electrolytic capacitors are very cheap compared to their cost several decades ago.
And modern ones are much smaller, so you can always easily fit them into tight spaces.
An annoying thing though is that you can't easily get axial types anymore (wires comming out of opposite ends of the barrel), so you have fudge things to fit in radial types.

Beware - there are a lot of *really crap* chinese caps out there; they will give you 6 months to a year of use before they fail. If you let someone else recap your stuff, be sure they put in reputable brands.
Vintage caps usually dry out gradually & slowly - they fail invisibly. Cheap modern junk caps usually burst & leak.
Click to expand...

Mouser has plenty of radial and axial caps! :thmbsp:
 
Increasing microfarad values will change the frequency response, and will often lead to oscillations.
Click to expand...

But just one point: electrolytics typically have a tolerance range of -10% to +150% or greater, so if you can't match *exactly*, not a calamity.
 
Thank you for the tips.
I stopped by a supply house to get some Deoxit ($20.00!) and asked about replacement caps. I was told that caps run anywhere fro 20% below and 30% above their ratings? He did say that a better cap may "sound" better but that may be the listener "thinking" he is hearing better quality.
He also said I could pretty much get whatever I brought in. I am going to start with a cheap pair of speakers before I tackle the Mach One's.
Then I will have a look at the STA2000.
 
Caps are cheap. The work is tedious and often difficult. Get one in backwards, or make a solder bridge, or break a wire, and you will likely have to be an experienced tech to find the problem and to fix it.

If the cap fails on an ESR meter, you will have had to take it out to measure it. Having done the hard part, why put the old one back in, since caps really are cheap?

One-by-one, triple-checking polarity on the board, with respect to silkscreen markings, and checking the operation of the unit after every board (as an aid to fixing it if it doesn't work right any longer), etc...all good counsel.

Enjoy,
Rich P
 
Fred Longworth said:
Look at how the original parts are mounted before you remove them. Do not rely on the "silkscreening" on the circuit boards -- this nomenclature is sometimes wrong!!! Remove and replace parts one by one. Do not pull all the caps at once, and then replace them en masse. This can lead to technical errors.
Click to expand...

Great advice Fred. Here's the PCB from a recap I did of my Yamaha C-2a preamp. I did them all at once and I kind of wish I had done them one by one, but I didn't have a schematic so I had to get the values somewhere.

I labeled each location on the board and plainly marked polarity. In the tighter areas, I also made a sketch on a notepad with locations, values, and polarity.

c2a1.jpg


merrylander said:
Then of course there is the old maxim - if it ain't broke . . .
Click to expand...

Which IS an old maxim.

However, I think in the case of crossover caps especially, often times you don't know what you are missing because you don't hear it. A refresh of those caps is easy to do and often reveals the true nature of the speaker in ways that are quite pleasant.
 
I asked this elsewhere but is there any sonic difference in switching film caps for electrolytic in the signal path where possible? What are the pros/cons? I'm prepping to recap my HK680i in the next few weeks.

Thanks,
Michael
 
shimniok said:
I asked this elsewhere but is there any sonic difference in switching film caps for electrolytic in the signal path where possible? What are the pros/cons? I'm prepping to recap my HK680i in the next few weeks.

Thanks,
Michael
Click to expand...

As a rule, film caps sound better than electrolytics. There are some exceptional electrolytics like Blackgate that might sound better than some film caps. The biggest cons for replacing electrolytics with film caps are 1) size - electrolytics are much smaller for the same value 2)price - electrolytics tend to be much cheaper
 
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