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Speaker crossover capacitor advice - Technics SB C-250

H

Hifibythekg

Super Member
Have just acquired a pair of Technics SB C-250 vintage speakers.

Generally they’re positively reviewed and I’d like to get them performing at their optimum.

Questions:

-What is the key quality one should seek in capacitors being used in a loudspeaker crossover (low leakage? or something else?) Please feel free to recommend a brand and series name.

-Also, has anyone changed the caps in this particular speaker or any others and heard a clear improvement?

Actually, if the existing caps test ‘ok’ on a cheap transistor tester.. is there any benefit to changing them?
 
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Capacitors should be bi-polar film types, 100V (or higher). Shunt capacitors larger than 10 uFd will be quite large for your crossover board so you may have to use electrolytics. They will be difficult to find in a radial lead configuration so you would have to stand the axial lead caps on end if you plan on using the original crossover circuit board. My preference for reasonably priced film caps would be the red Audyn Q4's. Available from Parts Express.
 
Since the parts are on a pcb you are stuck with what fits. You will not be able to get film caps that fit in that form factor, so just order Panasonic or Nichicon non polar electrolytic caps, radial, same capacitance same or higher voltage. You will not have much of a selection for impedance, leakage or ESR.
 
Hifibythekg said:
Have just acquired a pair of Technics SB C-250 vintage speakers.

Generally they’re positively reviewed and I’d like to get them performing at their optimum.
Click to expand...

I am not familiar with them. So, I have no opinion.

Hifibythekg said:
-What is the key quality one should seek in capacitors being used in a loudspeaker crossover (low leakage? or something else?) Please feel free to recommend a brand and series name.
Click to expand...

As noted above, crossover caps are non-polarized.

I find it best to visually inspect the crossover before ordering caps. If the original caps are still installed, I replace them with the same capacitance value. The voltage rating must be the same or higher. To get the exact capacitance value, wiring caps in parallel results in an equivalent capacitance of the cap values added together. That is, two 2uF caps in parallel is equivalent to a 4 uF cap. If the resistors and inductors look undamaged (no signs of physical damage or discoloration, such as from overheating), I leave them be and reuse them.

As for the type of caps, that is a divisive topic here. The least inexpensive option is to replace the caps with the same type - generally electrolytic. I only do this for cheap speakers not worth spending money on because of the cost. For example, I got some Radio Shack speakers for free. These particular RS speakers are not known for having high SQ, so I am recapping with electrolytic caps.

The next option is to recap with metalized polypropylene caps. I use poly caps for all caps, even the larger value caps if the speaker is worth it. Poly, film, and foil caps range from the inexpensive Dayton metalized poly caps up to those costing >$100 each. Some advocate adding a 0.3 to 0.5 ohm resistor in series with poly caps to account for the ESR difference from the original electrolytic caps. This is not necessary if the speaker has mid/tweeter attenuation control.

Decide how much you want to spend and shop accordingly. Parts Express is my go-to source for caps.

Hifibythekg said:
-Also, has anyone changed the caps in this particular speaker or any others and heard a clear improvement?
Click to expand...

In almost every case I hear a significant difference when recapping vintage speakers. Generally, I recap one speaker and then compare how it sounds to the other, un-recapped speaker. Out of dozens of speakers, there have been only two times where I could not hear a difference from recapping.
 
Hifibythekg said:
Actually, if the existing caps test ‘ok’ on a cheap transistor tester.. is there any benefit to changing them?
Click to expand...

Capacitors are susceptible to failing as they age. Electrolytic caps have an expected lifetime of 20 to 25 years and that is calendar age, not necessarily use time. As caps age, their capacitance values will change, often drifting upwards. The higher capacitance lowers the crossover frequency for high pass filters. Sometimes caps fail catastrophically, resulting in an open circuit (and no sound from the tweeter).

The equivalent series resistance (ESR) also increases as electrolytic caps age. For caps in high pass filters, high ESR is audible as a loss of highs, and, in severe cases, the speaker sounds muffled, as if a blanket is thrown over the speaker. The change in ESR is often more noticeable than the change in capacitance value.

I do not bother measuring caps when recapping speakers. The caps must be removed from the circuit to test. If you are going to that trouble, might just as well install new caps instead of re-installing the old caps.

Also, most inexpensive capacitor testers do not measure ESR at the frequency of interest (the crossover frequency and driver FR). The most audible parameter is ESR, more so than slight crossover frequency shifts. If crossover caps are going to be tested, then ESR is the parameter that should be tested and tested properly.
 
Haha, wow just wow!
Thanks for the learning resources link.
Also @RTally have you found, almost invariably, poly caps to sound better than electrolytics?
Or have a set of new electrolytics in some cases, and unexpectedly, provided a better sound quality?
 
Hifibythekg said:
Also @RTally have you found, almost invariably, poly caps to sound better than electrolytics?
Or have a set of new electrolytics in some cases, and unexpectedly, provided a better sound quality?
Click to expand...

I have used both electrolytic caps and poly caps. New caps always sound better than old, worn-out and degraded caps. I only use electrolytic caps on cheap speakers that are not that great of SQ. Accordingly, I have never compared electrolytic caps versus poly caps in equal SQ speakers.

From an electrical engineering viewpoint (I am an EE) and based on physics, poly caps have better sonic capabilities than electrolytic caps. Poly caps also have less ESR, so, in some cases, a series resistor should be used to obtain the same voicing as the original configuration that used electrolytic caps. The series cap is used to match the attenuation caused by the original electrolytic cap.

I never use electrolytic caps on any speaker that I plan on keeping. The only reason I ever use electrolytic caps is when the speaker is cheap and not worth spending a few extra dollars for poly caps. For example, I bought some Polk S4 speakers for $20. I recapped with electrolytic caps. They sound good (better after recapping), but I am not going to keep them and they are not really worth much more than $20, even after recapping.
 
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Thanks @RTally for another well-considered piece of advice. Appreciated.

My speakers probably fall between two categories (not so high end that they would benefit from the best poly caps investment, but could sound noticeably better with polys instead of electrolytics.) Having said that, they’ve previously been compared to your quoted Polk S4’s which probably didn’t overly impress you.

Given my predicament, could I draw on your experience and ask you to name your, say, three or four favourite reasonably priced poly brands/series that would fit within these spatially restricted crossovers so that I can see if I can source them in the UK?

(I presume I could use axial ones if I shield the long lead on an upright cap with shrink wrap..)

Thanks again.
 
My go to source for caps is Parts Express. I use their Dayton branded poly caps. I also like Audyn Q4 caps.
 
Hello @RTally and @dr*audio and @teal'c and @homebrew and others..
Thanks again for your excellent advice on this recap.
Trying to restart the project I’ve discovered what may be a big problem.
The original caps fit into a space of 20mm height (please see photos.)
Every type of cap that fits the electrical specs is physically taller than this.
Please could anyone suggest any caps that would do the job and fit the space?
I realise that they may not be the brand or model that would be your first choice but otherwise I may have to leave the speakers with old caps.. and never know their potential.
Again, many thanks.

Btw, Hi Fi Collective in the UK suggested Mundorf ecapsl - great, but they’re 38mm tall.

https://www.hificollective.co.uk/catalog/-c-61_68_227.html

My other go-to supplier is Farnell at:

https://uk.farnell.com/c/passive-components/capacitors

Do these guys have anything that would fit and probably be better than 25 year old caps?Screenshot 2022-09-21 at 21.53.41.png
Screenshot 2022-09-21 at 21.53.23.png

Screenshot 2022-09-21 at 21.53.11.png Screenshot 2022-09-21 at 21.52.47.png
 
You can install the capacitor on the opposite side of the PCB. The cap does not need to be between the PCB and the terminal cup. You can extend one or both of the leads to better fit the cap.

I suggest that you make sure the cap does not touch the resistors. It is best to keep at least a 1/2" air space from the caps.
 
Thank you guys super helpful replies.
@dr*audio my apologies, I made a big mistake by not correctly stating the specs of the caps in my UK spec set of speakers.
They are:
Bipolar 10uF 50V
Bipolar 8.2uf 50V
Bipolar 56uF 50V
All have to be under 20mm high.
I’m based in the UK, could I trouble you to see what would be most appropriate on the UK Farnell site at:
https://uk.farnell.com/c/passive-components/capacitors
(Unfortunately Digikey would add something like $15 for shipping of 6 small caps.)
Thanks @rRTally great ‘lateral thinking’ (or longitudinal thinking?) providing for maintaining high quality options if neatly fitting caps can’t be sourced.
Thanks again guys.
 
Your picture shows a 4.7uF. Where did you get the values above? All you have to do is go to the Digikey site, use the search engine, search for the value and then narrow it down by "nonpolar," "radial", and size. Then copy the manufacturer part number and plug it into the Farnell website.
 
The speakers were fitted with different cap values according to distribution region. My photo, for illustration of the crossover’s dimensions, was pulled from the internet. Attached is a link to Technics’ schematic. (I’ve previously looked inside to confirm two out of three of the values.)

Thanks @dr*audio for taking the time to suggest a very good ‘workaround’ for sourcing the caps using Digikey initially.

Unfortunately, when I try to get all three values from Farnell the relevant caps either aren’t in stock, discontinued, or only available for bulk orders.

May have to go down the route of Mundorf eCaps and fit them atop the pcb? Somewhat disappointed as I’d hoped a more economical solution could be achieved by sourcing some polys.


https://www.hificollective.co.uk/catalog/-c-61_68_227.html

https://www.petervis.com/manuals/technics-sb-c250-and-sb-c350/sb-c250-and-sb-c350.html
 
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