2 plus 2, Interfaces, bad capacitor

Read more on the Acoustat 2 plus 2 in our home audio section

John2004-02-23 22:21

I noticed one of my speakers ( Acoustat 2+2\'s) sounding very poorly and have narrowed the problem down to a bad cap in the transformer on the back of the speaker. The caps however have no values on them and I\'m not sure what the values are, can you help me find a schematic, or by chance can I be directed on how to find the value of the cap ( two identical large ones underneath the only circuit board ) ?? Thank you, John.


Andy Szabo2004-02-23 22:21

Identifying the capacitor is easy. It is either C4 or C5 on the schematic. Both are the same value: 0.01-uF, at 6000 volts. This capacitor connects the output of the high frequency transformer to the panels. A bad capacitor in this position can certainly make for bad sound. A schematic of the MK-121 interface is available from this site as part of the owner\'s manual.

Finding a replacement capacitor is not so easy. The 6000-volt rating is what makes it difficult. If you can find one in a polypropylene dielectric, that would be the best choice (that\'s what Acoustat used in the later years of production – your unit may have another type of dielectric). If you can\'t find polypropylene, the next best choice would be Mylar (i.e. polyester) or polycarbonate. Once you find a suitable replacement, I strongly suggest you replace all four. Not only will this reduce the possibility of other failures, but assuming that you don\'t find an exact replacement, you\'ll want all the same parts for matched sound characteristics.

Several possible sources are listed under Refurbishing, Available Parts. Others have successfully found replacements; hopefully you will have similar success. Note that the 6000-volt rating is a minimum: it is acceptable to use a higher voltage rating, as long as they are not physically too large.

Incidentally, some people have asked about using multiple capacitors in series/parallel combinations to obtain the proper capacitance/voltage rating. I don\'t recommend this practice. Placing capacitors in series to increase effective voltage rating is not safe: there is no guarantee that the voltage will divide evenly among the capacitors in the string. Also, the physical mounting of multiple capacitors can get tricky, especially with the close proximity of other high-voltage components. You\'re really best trying to find a single capacitor with the proper ratings.

Sylvo Schroeder2012-12-03 11:21

I have refurbished my 1+1 myself - basically changing the HF unit with a German compact unit after removing the old factory fitted one.

All the signal Caps are all ERO KP 1832 range at 1.6 KV - i have seen that 6000 volts is required but I have no problems with these - getting hot or fusing - although not easy to get.

After rolling Mundorf - VCap etc the best - and anybody would love the price.

Since I have done all that the 1+1 are performing very well with a definite improved response - soundstage - imaging and so on.

This is my last set of speakers - simply the best.

Sylvo Schroeder New Delhi 2012

Acoustatanswerman2012-12-28 19:13

Sylvo - Good news that you are happy with your capacitor modifications. However, I will stress again my advice not to use capacitors with such a low voltage rating. My guess is that you are using a small amplifier or that you don’t play them very loud. If you were to play the speakers anywhere near their limit, you WILL have problems eventually. By the way, the capacitors won’t get warm as a result of their low voltage rating. If they fail, they will do so abruptly, and possibly with explosive results.

Sylvo Schroeder2012-12-28 23:31

Dear Acoustatanswerman - thanks for your note - I will surely follow your advice - the only problem I have is to find a source where I can order the required caps - with high voltage capacity and similar audio performance as mine now - do you know a source?

Acoustat Answer Man2012-12-29 21:41

I should have been more precise in my advice, since you did not say which capacitors you replaced. Of the capacitors in the audio signal path, only the 0.01-uF capacitors on the printed circuit board should be rated at 5-kV. These are identified as C4 and C5 on the schematic. I do not know of a source for higher quality parts of this type. The original Acoustat capacitors were custom made.

The other capacitors on the primary side of the transformer may be rated as low as 100-volts.

Sylvo Schroeder2012-12-30 01:00

Yes I have understood - since it it only about C3 and C5 anyway - i am a little skeptical about getting the same audio performance as I have now when replacing these with the 5-kV ones.
Anyway thanks for your support.

Sylvo Schroeder2012-12-30 01:10

ohhhhh sorry - I mean to say C4 and C5 - thanks.

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