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Selecting Replacement Capacitors

sKiZo

sKiZo

Hates received: 92644 43.20°N 85.50°W
So ... which is more important? Voltage, or audio grade?

Working up to restoring a Sansui QRX-9001. I can find "audio grade" capacitors for all values, but the voltages are a bit of a problem. For instance ...

3.3uf - The unit requires 13@16v, 8@25v, and 8@50v. I can only find them in 50v in audio grade, but exact matches are available as general purpose caps.

Fish or cut bait?

I'm told that even new stock general purpose caps tend to be a big improvement over what was available back in the day. Also, rumor has it that capacitors need to operate at a certain percentage of their rated voltage to load up properly? There's also the argument that the mfrs did tend to undervalue their caps regularly to reduce costs. Size and fit doesn't look to be an issue, as same voltage new caps tend to be much smaller anyway.

My choices (sticking with the 3.3uf example) are then:

- Match the spec'd voltage in all cases. Audio grade when available in the correct voltages, then general purpose.

OR

- All Audio grade and up the voltage to the next available value if an exact match isn't available. That would mean replacing the original 16v with 50v and running them in circuit at something like a third of their rated voltage.

Hep me! Hep me please!!
 
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If we are talking about 3.3uf polarized electrolytic's, then the value is small so manufacturers are not going to make low voltage ones as they would be tiny, 50v would probably be the lowest ones they make.

It would be fine to use those if they fit.

Are you sure it uses so many 3.3uf's?
 
HypnoToad said:
50v would probably be the lowest ones they make. It would be fine to use those if they fit.
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I've always thought that. Just did a QR4500 that way, and that wasn't my first. But ... this is THE box I've always wanted and I want it to SING! That and the amount of work that will be involved wants me to get it right. Anyway - I can find exact matches for value and voltage (even the 16v), but they're not audio grade, hence the question.

HypnoToad said:
Are you sure it uses so many 3.3uf's?
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Don't know if you're familiar with the QRX9001, but I hear tell it has somewhere around 260 electrolytic capacitors total. Somewhere there's a rubber room full of gibbering audiophiles who took refurbing one of these things on. Not being a glutton for punishment, I only plan to replace around 177 of them. <G>

I'm also trying to pin down how many critical electrolytics in the audio path would benefit from the addition of a polyproplene bypass cap. I'm thinking around 60 there.

And that's only the start of the fun. The rig is also (in)famous for having issues with failing pass thru connections on one of the double sided boards. Mine exhibits some of the classical signs of this problem. There's 50 of those that need to be desoldered and pinned - something Sui should have probably done in the first place.

Should pretty much kill a good bit of the winter I'd think.
 
Ah. Found it.

Here's a link to the post that got me scratching my head here.

http://www.audiokarma.org/forums/showpost.php?p=2925403&postcount=2

Caps work best when used somewhere at around 75 to 95% of their rated voltage (I shoot for about 85% when I have that luxury to allow for line voltage fluctuation). Used at much lower voltages (like 50%), they cannot manufacture the oxides needed to develop their rated capacity.
Click to expand...

Problem being - that's the only reference I can find that addresses the issue.
 
I've read that several times, about electrolytic, that they work as designed when they are at the rated voltage.

But anyway I'd choose Audio grade instead or general purpose. I recapped my mid-fi Philips, full of general purpose caps, replaced all of them with Elna Silmic II, Now it's Hi Fi. It sounds much better now.
 
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Interesting. I see those also cover the other smaller values @63v that I couldn't find in the Elna Silmic II list. If as you say voltage isn't an issue with these in the circuit, the 63v would be the smallest package available.

I glanced at those earlier and wondered if the pin spacing would be an issue. They look like a fixed width peg mount (5mm) and I was wondering how flexible the pins were for mounting? I do know the smaller electrolytics typically are 2.5mm spacing, but then you just bend the legs as needed. Not sure if I'd want to kludge the WIMAs into the boards by stretching the pins. Yet more joints to fail ... you run into any fitment issues on yours?

roger2 said:
EDIT: I should add that the leads on these are short, so lead spacing would need to match the PBC pretty closely.
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I'll see your edit and raise you one. <G>

About what I'd earlier figured. Seems they WOULD be usable if I were to add .047mf polypropylene bypass caps to the chain where ever I used the WIMAs. Those have long legs - run those into the board and attach the shorter pins in the film caps to those.

Probably a stupid question - they ARE polarized? Also, I see they're polyester. I was under the impression that was verbotin in the signal path?
 
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avionic said:
Digikey also stocks the Elna SilmicII's.
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Sure about that? I just checked DigiKey and couldn't get a match. Only thing I saw was some general purpose stuff from Elna America.

Then again, DigiKey's search engine seems to suck ...
 
EchoWars said:
Silmic II is sort of a marketing name. The industry name is Elna RFS Series.
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Thanks for the heads up. I was able to find that on Digikey, but drat ... they're also missing the values everyone else is missing. They have 3.3mf, but only in 100v - which I guess brings me back to my original question. How close should I be matching the voltage?

Found these guys too :

http://www.partsconnexion.com/capacitor_ele_elna_rfs.html

They did have a few more of the exact matches I needed.
 
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sKiZo said:
Thanks for the heads up. I was able to find that on Digikey, but drat ... they're also missing the values everyone else is missing. They have 3.3mf, but only in 100v - which I guess brings me back to my original question. How close should I be matching the voltage?

Found these guys too :

http://www.partsconnexion.com/capacitor_ele_elna_rfs.html

They did have a few more of the exact matches I needed.
Click to expand...

Good source but in Canada so shipping is a little longer and a little more $. Try and get your oder right the first time and get everything you need in one order. As mentioned you can go up in voltage but watch the size so you dont have to re-order.

Cheers,
Bob
 
sKiZo said:
Thanks for the heads up. I was able to find that on Digikey, but drat ... they're also missing the values everyone else is missing. They have 3.3mf, but only in 100v - which I guess brings me back to my original question. How close should I be matching the voltage?
Click to expand...
So? Go to a 4.7uf (don't use the 'm' for µf, it confuses things...use ALT+230 for the 'µ', or just a lowercase 'u').

Voltages...try to match, but if you can't, jumping up one or two steps isn't a real big deal.
 
To ensure maximum reliability many manufacturers employ military deratings for electronic components used in their products. For electrolytic capacitors the maximum recommended in circuit voltage stress is 80% or less of the component’s rated voltage. The actual voltage stress is usually much less than that. Electrolytics are notoriously non-linear. Their capacitance decreases as voltage and frequency increases. The capacitances of Polypropylene types are not as voltage and frequency dependent. It is this stability makes them better suited for audio. If you can fit a higher voltage cap in place of the older one its ok. There’s no harm in it.
 
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I've got my Elna Silmic at partsconnexion.com (canada). To argentina it was the cheapest shipping.

I've got Nichicon FG in those values where Elna was not available.

Many people suggest Panasonic FM series for the bigger caps (power supply caps). they are 105º instead of the regular 85º caps.

I've added 2.2 , .3.3 or 6.8 film by passes only to 1000 uF caps or bigger
 
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EchoWars said:
So? Go to a 4.7uf (don't use the 'm' for µf, it confuses things...use ALT+230 for the 'µ', or just a lowercase 'u').

Voltages...try to match, but if you can't, jumping up one or two steps isn't a real big deal.
Click to expand...

My bad on the mufµ thing ... I'll try to watch myself. I got most of em right up till then. <G>

The one or two steps never bothered me - can't get 6.3v? 10v should do. 16v would be kinda pushing it according to some as it's more than twice the rating spec'd and <could> have issues ... once again, according to some. Problem being, I was only finding cap voltage values of triple or MORE. Even that never bothered me much before, but I so want to get this one right.

Some good info here tho - I'm real close to a Plan B. Come to find out, I can get exact match for most of what I need in the Elna Silmic IIs, and supplement those with the WIMAs when all else fails. Those ARE non-polar AND voltage isn't an issue as it would be with an electrolytic. Yes, they ARE polyester vice polypropylene, but is that really a problem?

My major concern then would be fitting the WIMAs to the boards. They're short and stout ... at least we've got that in common. I did find some info on using molex posts to stretch them if needed. Crimp and solder, insulate, then solder the molex pin to the board. Kewl if it works.

Anyway ... I think I'm making progress here. Baby steps ... baby steps.

PS - any truth to the rumor that the Elna Silmic and WIMA caps give a "warmer" sound? I do miss that from my QR4500. QRX9001 does certainly run rings around it for power and quad output, but tends a bit towards shrill comparatively. Wouldn't mind fattening it up some while I'm in there.
 
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elnaldo said:
I've added 2.2 , .3.3 or 6.8 film by passes only to 1000 uF caps or bigger
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I was working under the assumption that the bypass caps were even more important from around .47µf to 4.7µf to smooth transients?

There, I've seen recommendations for adding either a .047µf or 1µf in parallel ... and that voltage rating on those isn't critical, and that polypropylene is preferred, but polyester is fine.

See? I'm not quite as confused as I once was. That almost made sense to me! <G>
 
Plan c

EchoWars said:
So? Go to a 4.7uf (don't use the 'm' for µf, it confuses things...use ALT+230 for the 'µ', or just a lowercase 'u').

Voltages...try to match, but if you can't, jumping up one or two steps isn't a real big deal.
Click to expand...

Interesting ...

Pulled out my calculator and did some math. I hate math, but you gots to do what you gots to do.

3.3µf +20% = 3.9µf
4-7µf -20% = 3.8µf

OR

... an overlap of .3µf assUming high end of range tolerance on the 3.3µf and low on the 4.7µf, or a 14% chance of being right on the money, once again assUming Sui factored in the tolerance when designing the circuit.

Did I mention math isn't one of my strong points? Maybe I'm overthinking this. <G>

** Some of us DO tend to overlook the wide tolerance of smaller caps ... not to mention temperature characteristics.
 
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