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Multi-Way Conventional loudspeakers with crossovers

Technics  SB-10 Crossover Questions
Technics  SB-10 Crossover Questions
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Old 6th February 2018, 01:39 PM   #1
TechnicsSB10fan is offline TechnicsSB10fan
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Default Technics SB-10 Crossover Questions

Greatings Ladies and Gentlemen,

This is my first post on diyaudio

I have just been happily reunited with a pair of Technics SB-10 speakers and a Technics SU-V9 amp.
I had the same equipment back when they first came out, so when given the chance to acquire again I did not hesitate.

I since have been reading about vintage equipment and how the capacitors decay over time.
I see this as a opportunity to upgrade those electrolytic ones that can cause problems.
The speakers will be a lot easier to attempt so I will start there first.
After a week of reading on the net I am a "little" bit more knowledgeable, but need a few hints;

There are three electrolytic capacitors in the crossover on the Bass circuit;
One 47uF 100v electrolytic in parallel with a 0.47uF 100v metalized polyester film C1 and C2 on the diagram. (is this configuration called a bypass?)
Two 330uF 50v in parallel with each other and in series with the Bass speaker.C8 and C9.
The 47uF 100v appears to be an easy swap for a polypropylene film cap of the same 47uF value but 250v. I am thinking of using the Clarity Cap CSA would this be a good choice?
When it comes to the two 330uF 50v electrolytic caps I am stumped, there does not seem to be a match in a polypropylene film type. Probably have trouble fitting them in anyway.
Should I just use quality electrolytic caps of the same value? If so any suggestion on the maker?

Below is a schematic of the crossover, (hope it is legible) any advice on the design and possible upgrades would be a great help as my knowledge in this area is not great. I would appreciate any advice given.

Best
Regards
A confused
Technics SB-10fan

Specifications
Type 3way 3 speaker system
Woofer: 32cm honeycomb dicc
Midrange: 8cm honeycomb disc
Tweeter: Leaf Tweeter (full surface movement type)
Impedance: 8 ohms
Input Power: 150 W, Music
100 W, DIN
Output Sound Pressure Level: 87 dB/W ( 1.0 m)
Crossover Frequency: 400 Hz. 4000Hz
Frequency Range: 28Hz~125 kHz (-10dB)
Dimensions: 40.2(W) x 71.1(H) x 31.8 (D) cm
Weight 32.0 Kg

Last edited by TechnicsSB10fan; 6th February 2018 at 03:23 PM.
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Old 6th February 2018, 01:49 PM   #2
Mooly is offline Mooly  United Kingdom
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Technics  SB-10 Crossover Questions
Welcome to diyAudio

Yes, adding a smaller film cap across an electrolytic is a form of bypass, the film cap maintaining a low impedance as frequency rises and any self inductance effects and losses of the electrolytic come into play.

ALL the electrolytics in the speaker will be non-polarised or bi-polar types meaning they are not polarity conscious. Do not attempt to use ordinary polarised parts for these.

You can make a bi-polar cap by connecting two caps in series joining either plus to plus or minus to minus (it doesn't matter which) and choosing the caps to be twice the value of the original. So two 680uF 63V caps would make a 340uF bi-polar.

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Old 6th February 2018, 02:11 PM   #3
Mooly is offline Mooly  United Kingdom
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Technics  SB-10 Crossover Questions
Attaching images directly to the forum is easy and is the preferred option as they then remain with the thread:

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Old 6th February 2018, 02:31 PM   #4
TechnicsSB10fan is offline TechnicsSB10fan
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Thanks for the quick reply Mooly, yes I get the bi-polar being necessary
330uF 50V are readily available in electrolytic.
As the two 330uF 50Vs are in parallel therefore they must be bi-polar, correct?
The originals are radial, so would it be acceptable to use an axial in a vertical position with one short leg in the board and the other long leg running down the side of the cap to the board? I see some Jantzen bi-polar 330uF 100V axial caps. would 100V vs 50V matter? so many questions...
not being able to see the schematic, I need to find another way of getting this up?
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Old 6th February 2018, 02:48 PM   #5
TechnicsSB10fan is offline TechnicsSB10fan
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Thanks Mooly,

SB-10 crossover schematic


IMG_20180206_221411[1].jpg
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Old 6th February 2018, 06:02 PM   #6
Mooly is offline Mooly  United Kingdom
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Technics  SB-10 Crossover Questions
Yes they are bi-polar, as are all the electrolytics in a crossover. Swapping radials for axials is fine as long as they are secure (dab of hot melt glue to stabilise them but don't use quick curing silicone rubber as it gives of acetic acid and will corrode metals) and the leads not liable to short to anything.

Higher voltages are fine as long as the cap doesn't get to large physically.

Those variable controls might be worth a look at and a clean. They can typically go intermittent as tarnish builds up on the wiper and the resistive wire being swept by the wiper.
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Old 6th February 2018, 07:03 PM   #7
picowallspeaker is offline picowallspeaker  Italy
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I would ditch the overvoltage circuitation; also the fuses ( resettable ones..)...well, I would first keep the crossover outside the enclosure. The variable L-pads, too.

The capacitor(s) before the woofer indicate that the closed enclosure ( pneumatic suspension ) offers a load specific for the woofer in a way that it behaves differently than without those. It's a matter of capacitative behaviour of the impedance argument before Fs and inductive type after Fs ( somehow, maybe inverted, ha !! )
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Old 6th February 2018, 08:58 PM   #8
TechnicsSB10fan is offline TechnicsSB10fan
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Thanks for the tips guys.
I will pull one of the variable controls and see if it will come apart for cleaning.
I was a little concerned that mounting a cap with one long lead exposed that it may pick up some electrical noise, read that somewhere
Thanks Mooly.

I can see your point picowallspeaker regarding the excess circuitry and it would be nice to dismiss it all, but I am a little concerned, for now that I would be removing a line of defense which could save me from destroying one of these very hard to replace speaker units, especially with me making modifications to the capacitors etc. I would consider doing that last if all other modification prove successful first. An external crossover makes a lot of sense and I would consider that too if I was building a complete crossover from scratch but I would have to learn a lot lot more before I would consider that.

Interesting is picowallspeaker`s explanation of the capacitors before the woofer, yes indeed the enclosures are a sealed design.
I get the part, I think, about capacitance behavior of the impedance, and therefore I probably should keep it the same value to keep the woofer behaving correctly?
I am not following the second part, quote "...impedance argument before Fs and inductive type after Fs ( somehow, maybe inverted, ha !! ) "
Could you please expand on what you mean here this is all new to me, and I am not understanding this part.

Thanks for the input gentlemen I am making progress now, I think!
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Old 7th February 2018, 03:58 AM   #9
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A picture of the SB-10 crossover, with the 3 electrolytic caps in blue.
I guess those are not air coils?

IMG_20180207_125459.jpg
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Old 7th February 2018, 07:50 AM   #10
Mooly is offline Mooly  United Kingdom
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Technics  SB-10 Crossover Questions
The controls may not come apart without damage, but they be an 'open' type construction that allows a suitable cleaner to be used.

If they were a bit noisy and intermittent, and if you normally 'set and forget' then they could be replaced by fixed resistors to make up a standard L pad attenuator.

There is no real problem with noise being picked up because all the impedances are (in the scheme of things) so low.

Those look like ferrite cores with the number such as 682 and 471 being the value in micro Henry's. The last number indicates the number of zeros to add.

So 682 = 6800uH or 6.8 milli Henry. 471 would be 470uH or 0.47 milli Henry.
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