How to fix Technics SB-T20 Speakers? - diyAudio
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Old 10th September 2012, 06:35 AM   #1
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Default How to fix Technics SB-T20 Speakers?

I have a pair of these speakers, and they've been great. I picked them up at a thrift store a number of years ago. The bass on one has become very distorted and I think I may run into the same problem as described here: Technics SB-T20

I have never repaired a speaker before, but I would like to try to repair them rather than just ditching them. They work fine otherwise. Any help would be much appreciated. Total DIY Audio noobie here. Thanks.
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Old 10th September 2012, 08:53 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Click the image to open in full size.

Bayonet mounting is like a camera lens, usually rotate counterclockwise
to remove, used quite a bit in that period, its not common now at all.

Some points on the driver that would allow this are a clue to it being the case.

rgds, sreten.

apologies to the OP in the other post, don't know why I didn't reply.
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Last edited by sreten; 10th September 2012 at 08:59 PM.
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Old 4th February 2014, 03:42 AM   #3
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Unhappy I got the woofer out

I'm still having the problem with the woofer. It buzzes, is the best way to describe it. I tried connecting a different set of speakers and the problem disappeared, so I know it's not my receiver, a Marantz 2250.

I managed to get the woofer off. The metal grill on it can be pried off with a flat screwdriver. There are two indentations in the edge of the grill at about 5 o'clock and 7 o'clock. I didn't see the indentations at first, and just stuck a screwdriver under the edge of the grill. Once that is off, there are four screws to remove. The woofer has a rubber gasket around it, which might be lightly glued to the cabinet, but it did come off with not too much effort. Once out, there is simply a positive and negative connection. I took a bunch of pictures of the circuitry inside the cabinet, and of the woofer, but I don't seem to be able to upload them.

I sprayed the contacts with contact cleaner, checked to see that everything looked good. Nothing seemed loose or torn. I noticed on eBay someone is selling a manual for these speakers, I was considering buying it. I'm not an audio technician, nor do I know electronics, so I think I'm at the end of my options for DIY fixing. It's a seven-inch woofer, and I'm thinking I might just be able to pop in any seven-inch woofer in place of the one in there. It's too bad, as the sound was really exceptional, and maybe more important, I like the way they look. They are the same exact height as the cabinet I have my TV and stereo on, with the same fake walnut finish. I would love to get a replacement for that one speaker. I guess I'll just have to keep searching eBay and thrift stores.
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Old 5th February 2014, 12:36 AM   #4
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Sometimes the leads between the terminals and the voice coil get displaced enough to slap against the cone. There's probably a conventional cone driver under that flat front, I have a version of these, so there's an extra layer of stuff that might have come unglued enough to buzz. Anything that was glued together, including the crossover, can buzz. Good Luck!
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Old 5th February 2014, 06:53 AM   #5
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Default Glue-gun woofer

It turns out the foam surround on the woofer was completely split. The whole centre part wasn't connected to the outside edge. I don't really know anything about speakers so it wasn't until I compared it to the other one that I realized it wasn't supposed to be torn all the way around. It's a very thin type of foam that must have just worn through eventually. Seeing as it was basically toast anyway, I ended up hot-gluing it back together. It seems to be working fine. So far. I don't think the speakers are rated high enough for my receiver. I must have blown them.
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Old 5th February 2014, 07:55 AM   #6
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Speakers not being rated high enough usually ruins the voicecoils by slamming them into the magnet system. What you have is common on older speakers, the foam rots away. Nothing to do with being used hard.

You can buy refoam kits for many different speakers and there are some good guides on youtube - the priciple is the same for all speakers.
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Old 5th February 2014, 09:14 AM   #7
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Thanks! It's good to know I'm probably not to blame. I'm realizing how much there is to know about this stuff. I wonder, what would be a good set of speakers to go with a Marantz 2250 receiver? I use it for listening to music and movie audio from my computer via a mini-to-RCA jack. I have my TV set attached as well, as a secondary sound source. I've been thinking of getting a surround system or at least a digital-only HDMI input receiver, but I like the Marantz a lot. I've managed to cobble together an all-Marantz system of receiver, turntable and two tape decks, but I really only use the receiver.
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Old 5th February 2014, 09:26 AM   #8
Lojzek is online now Lojzek  Croatia
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Chellspecker,

if you are going to get new surrounds for the drivers of yours,
look for softer ones. Too stiff would shift resonant frequency
much to the right on the scale and make it sound weaker in
bass.
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Old 5th February 2014, 09:34 AM   #9
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Is there anywhere I could get replacement drivers of the same model as in the original speakers? I've done a search for them by model number but can't find anything. And failing that, what would be a good replacement? Do you really think I can resurrect them with new surrounds?
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Old 5th February 2014, 09:47 AM   #10
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If you can't put new surrounds in, just don't bother with anything else. Trying to put in replacement drivers will likely mean work to the mounting hole and the crossover will probably be wrong.

Depends how fussy you are though, some people are happy with the result of this kind of bodge.

Technics tended to use custom drivers, I doubt you will be able to find OEM replacement.
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