Output capacitors

[-=Zepplock=-]

Hello,

I have an 1989 Sansui amp, which has leaking output(?) caps. They are rated 55v , 750mf.

What whould the best replacement for them?

p.s. the sound is ok except for high frequences.

[Jonathan Bright]

The standard advice in these situations is that you can't go too far wrong by replacing it with a capacitor of larger value and greater working voltage. so going to 1000uF at 63 volts would be a good start. (By the way I take it that 750mf is 750 uF.) That is not very large for an audio amp'. This is particularly so if you use 4 ohm speakers. Most of the capacitor coupled amps around will ususlly ragard 2,000 uF as a starting point. Zepplock, many people recomend running a small higher quality plastic/film cap in parallel with large electrolytics. It can reduce the higher impedence of electrolytics at high frequencies. That may assist the high frequencies.

[-=Zepplock=-]

Thank you for your reply.

So if I want to try to put 2 caps in parallel, what would be a general advice on the values?

If I take 1000uf/63v electrolytic - what's the parameters of plastic/film should be?

Thank you.

[Jonathan Bright]

Hi.Zepplock. I've been fairly cautious with that earlier response. Some people go mad on this stuff and use v.big values. I friend has an old English Sudgen that starts at 10,000uf. I suggest you take the old cap out of one channel and fit something bigger and then do a comparison between it and the old one in the other channel. Bigger cap will improve the bass, The rule is. always use the same voltage or larger. That's a safety thing. BTW the bigger electrolytic is "polarized" IE it has +ive -ive pins. Your new one should go in the same way as the original one or you will have problems. With the small film/plastic cap there is no rule about size or polarity. You can't fit it "back to front" okay? Try a 0.1uf to start with. Again, voltage above 50. As to the type, try these. The general preference these days seems to be Polypropolene, polystyrene, polycarbonate and lastly polyester. Tantalum and ceramics are getting "bad press" in some quarters. You can't do much damage in this area where you are working. Experiment and see what it sounds like. That's half the fun. (The other half is telling poeple you made it yourself and not paying a serviceman.)

[K-amps]

Also that cap needs to be Bipolar(actually non-polar). Two polar caps back to back would work technically, but I an not sure how they'd sound.

With 1000uF NP, I'd use 10-47uF further bypassed 0.1uF to 1uF.
The latter being Paper in Oil types.

[Jonathan Bright]

K amps, I think you'll find just about every output cap is a conventional polarized unit as there is usually half the supply voltage on the amp side. You only need bipolar in the xover network. As long as the new one goes in the same way as the old one he should be fine. How much are you paying for you Paper in oil cap?!!!!!! I agree about the quality though.

[K-amps]

I got them a while ago from some guy in East Europe selling Russian Military Surplus. I think his name was "Gintaras" and his eBay ID was kwtubes... but I am not sure anymore.

The 1uF PIO 250v was a 1.5" cube... Huge cap.

Ok found the guy, they were like this auction...

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

[hermanv]

Ok there is nothing wrong with improving a product. As an audiophile I too get lost in microscopic details but we are talking about a Sansui.

Not that there is anything wrong with Sansui per se but an oil filled bypass?

Older amplifiers occasionally took advantage of limitations of some parts to mask a problem with others. May inexpensive transistor amplifiers have a midrange grain or hardness that is actually improved by not having perfect power supply caps.

I agree bigger is probably better but a listening test is advised before going overboard.

[K-amps]

Sure but he asked what to use as bypass... you are surely entitled to your opinion.

By the way, as far as schematics goes, some Sansui's have a more sound topology than some high-end amps I'd care to mention. The high end amps do usually have better selection of quality components though.

As far as sonics go, caps sound different, you can use a PIO and get harsh mids or use a Tantalum and get creamy mids.... No absulute truths in using caps in signal paths... have seen em all.

[-=Zepplock=-]

I think I'll take Jonathan Bright's advice and start with experimenting on the one channel.

I'll put some 1000uF/63v caps that I saw in local radioshack and then maybe 1uF caps and do i listening test.

Thanks to all who participated.
I'll post results.