Replacing electrolytic caps in crossovers - what voltage rating to use?

[system7]

100V, 600uF plastic film (MKT) will be mighty big and mighty expensive if one cannot locate a special offer.

Back in the day, you might have had an interest in protecting a bass unit from subsonics, mainly thumps from your footsteps picked up by the tonearm from a turntable. These days, a CD output simply doesn't have subsonics.

So the series bass capacitors are no longer needed, IMO. Still a terrible design though.

 

[AndrewT]

Back to your comment:

They hardly do anything.

 

[maty tinman]

You can search here: Capacitors | Hifi Collective

600 uF is too big with "audiophile" caps. 270 + 330, and expensive.

Mundorf Mcap EVO Capacitor

-> http://www.hificollective.co.uk/catalog/-c-61_68_428.html

Jantzen Cross Cap

-> http://www.hificollective.co.uk/catalog/jantzen-cross-cap-capacitors.html?page=1

Jantzen Bi-polar Electrolytic Capacitors

-> http://www.hificollective.co.uk/catalog/-c-61_68_463.html

 

[eriksquires]

At 600uF times four, yes anything but electrolytics will be excessively expensive, and I anyway gather that the quality of woofer caps isn't all that critical. Would you agree?

The bypass is interesting. Do you mean to parallel the bipolar electrolytic cap with a film cap of something like 10 or 22 uF? And why is that good?

Please see this blog, and look below at the section labeled "Bypassing"

 

[maty tinman]

Next week I will to try to bypass the tweeter capacitor of my KEF Q100 monitors. Of course, spending a minimum: 6.5 €.

KEF Q100 Uni Q bookshelf speakers. 5.25" coaxial with front bass reflex. - Página 4

To English -> https://translate.google.com/translate?sl=es&tl=en&js=y&prev=_t&hl=es&ie=UTF-8&u=http%3A%2F%2Faficionados.foroactivo.com%2Ft342p45-kef-q100-uni-q-bookshelf-speakers-5-25-coaxial-with-front-bass-reflex%2316155&edit-text=&act=url

And after I will change the original capacitor and resistance of the crossover with Jantzen Superior Z-Cap and Mundorf M-Resist Supreme 20 W.

Step by step, I will check by myself into a system that sounds great now.

If I do not notice improvement that no one doubt that I comment on it!
​

 

[sreten]

Hi,

FWIW series caps on a sealed bass unit are a well known technique.
Not very popular nowadays, but can hardly be called useless.

Done right it reduces bass Q and offers some subsonic protection.
Can be modelled with the free version of Basta!.
http://www.tolvan.com/index.php?page=/basta/basta.php
See : http://www.humblehomemadehifi.com/download/Humble Homemade Hifi_Black Box.pdf

Popular in quite a few Kef models and notably the Goodmans Maxim 2.

If you omit the capacitors increasing box stuffing is a good idea.

rgds, sreten.

 

[Tom4s]

Thanks for all of your useful suggestions, ideas, opinions and links!

I have a turntable that is still used sometimes, and I don't want to stuff more wool into the speaker. The amp's max rail voltage is just under 100V, so I'm looking at using 2x330uF 100V bipolar electrolytics from Jantzen. Maybe bypassed with 6.8uF Jantzen std z-cap...

It's interesting that the polarity of the tweeters and mid-bass has been reversed. This is what the sales brochures called 'phase aligned' back in the day!

When looking at the schematic for what values caps I need, I discovered an error for the tweeters. It says "3.16uF (.33+.33+2.2)" ...it doesn't add up! I have to open a speaker before ordering those caps. Oh well. I probably should replace the screws holding the woofers with bolts.

 

[wdecho]

I have found lately that motor run capacitors are the best sounding of all the ones I have tried including PIO. Be sure and use the oil filled ones. Very high AC rating which makes them 1.4 times that value for DC, a film capacitor, generally a low ESR value and can be found a very reasonable prices especially on Ebay. There is not much to not like.

 

[Tom4s]

Where's the smiley? That is a joke, right??

If not a joke, how have you tried them - in series or parallel with the speaker element?

 

[ICG]

Back in the day, you might have had an interest in protecting a bass unit from subsonics, mainly thumps from your footsteps picked up by the tonearm from a turntable. These days, a CD output simply doesn't have subsonics.

So the series bass capacitors are no longer needed, IMO. Still a terrible design though.

The capacitors are part of the bass design, the high pass flattens the bump in the bass and reduces the needed volume of the box, it lowers the Qt. To leave them out makes the speakers boomy and unprecise. The excursion will increase too. So it's not advised to leave them out, especally if you want to listen loud, because of the latter. The impedance in the bass will drop further too, also not necessarily something one would want at this speaker.

 

[Tom4s]

So it's not advised to leave them out, especally if you want to listen loud, because of the latter. The impedance in the bass will drop further too, also not necessarily something one would want at this speaker.

I have ordered four MOTOR START CAPS! Voltage rating is fine, and they're cheap so no big deal it they don't work out.

One of the woofer voice coils is marked 2 Ohms, in parallel with a 4 Ohms vc, so you're quite right about not wanting to decrease the impedance!

The schematic is correct about 3.16uF for the tweeters. It's made from three caps: 0.33 + 0.33 + 2.5uF (and not 2.2uF as written in the schematic). I'm replacing this with 0.47 + 2.7uF, because I can't find any 2.5uF caps from the good brands.

Cheers,
Tomas

 

[ftpols]

Elko BP electrolytics are about 1/2 the size of the equivalent Bennic caps and won't break the bank.
See https://www.intertechnik.de/Shop/Cross-over-parts/Capacitors/Rough-foil/1768,en,606

 

[Tom4s]

Elko BP electrolytics are about 1/2 the size of the equivalent Bennic caps and won't break the bank.
See https://www.intertechnik.de/Shop/Cross-over-parts/Capacitors/Rough-foil/1768,en,606

Thanks for the tip, but I am concerned about the voltage rating "ELKO RAUH 100Vdc/35Vac rated range"...

These are to be used in series with one 4 ohm voice coil and the other a 2 ohm voice coil, to block subsonic signals. There can in theory be up to 100 V AC from my amp.

To use electrolytic caps, I think it would be better to connect two large caps in series and reverse polarity (i.e. create my own bipolar caps). For the two speakers, I would then use 8 caps. Here are 12 for a good price: clicky link

 

[Tom4s]

I have ordered four MOTOR START CAPS! Voltage rating is fine, and they're cheap so no big deal it they don't work out.

Those caps took a long time to arrive. When I was later checking them out, I noticed there was something rattling around inside three of them. I complained to the seller that I expected caps to have no moving parts inside... Still waiting for replacements to arrive.

 

[TMM]

Those caps took a long time to arrive. When I was later checking them out, I noticed there was something rattling around inside three of them. I complained to the seller that I expected caps to have no moving parts inside... Still waiting for replacements to arrive.

I often use 250Vac fluorescent lighting capacitors as a cheap source of polypropylene caps. Rattling caps is very common as the 'can' is just a casing to protect the metallised slug inside and often the fit is not as snug as possible. I guess rattling is not such a problem for a lighting installation .
The 'can' is usually plastic on the ones that I buy so it's easy enough to pop the end off and drop some hot melt glue or epoxy in there to secure the slug. Looks like the ones you have might be a crimped metal can like they would use for an electrolytic capacitor - it may still be possible to open the end (uncrimp or cut open) and see if you can do the same to stop the rattling.

 

[Tom4s]

it may still be possible to open the end (uncrimp or cut open) and see if you can do the same to stop the rattling.

These are all metal cans. I tried to open one, but it seems it won't be possible without destroying the can (with the tools I have). The rattling comes only from near the top. I suspect there are some nuts or metal scrap thrown in to add some dead weight; a common technique in Chinese manufacturing to trick the QA stage...

 

[canvas]

Those caps took a long time to arrive. When I was later checking them out, I noticed there was something rattling around inside three of them. I complained to the seller that I expected caps to have no moving parts inside... Still waiting for replacements to arrive.

How are your large starter caps? Are they better than electrolytic in crossover?

 

[Phenoholic Anonymus]

I often use 250Vac fluorescent lighting capacitors as a cheap source of polypropylene caps.

Highly appreciated! The motor run capacitors are mostly 450Vac and way to big for most replacement use.