L20T3 recap advice and driver resistance

[Nostoppin1]

Hello all, this is my first post here. I love this website and, having found myself here multiple times as a result of internet searches, figured it was time to join in.

I'm looking for wisdom on the DCR of my drivers and recommendations for which caps to choose for replacements.

I just picked up a pair of L20t3's to use one as a center channel for my L100T's. Planning to recap the unused speaker, I removed the 035TiA and 115H-1 to more easily take the X-over out.

As a lark, I put the ohm meter on the drivers and I'm a bit bummed out. The DCR min-max on the 35Tia is 3.5-4.2 ohms, and mine is 4.1. Right on the edge.

The 115H-1 min-max is 3.8-4.6 ohms, while mine is 4.9. I replaced the batteries in my meter and retested, seeing a .1 ohm drop to 4.8. Still out of range.

How bad is this? What makes driver resistance change over time? Would it mean using different cap values for the new ones?

as far as caps: the little .01µF ones. My friend google says these are bypass caps and should be film. Would you agree? what tolerance?

The 100µF electrolytic: replace with film? would it matter which type of film - polypropylene? there's so many types!

The big yellow one: I get the value, 4 ohm. I get the K being +/- 10%. it's the CEC that confuses me. is it ceramic? internet searches don't seem to have the answer, or I'm not asking the correct questions.

Thank you for your time! Peace!

 

[powerman]

Hello and welcome, here is my take on your issue. First using the L20T3 as a center channel would not be the best fit sonically. In practice the center channel is usually matched to the Left and Right speakers in this case L100T’s. If you play it loud with movies or music the L20T3’s will come up short on output compared to the L100T’s. Your DCR values are OK as they are of an average value and the one reading high is not bad. The crossovers JBL made for them with cost considerations at the time. Solen capacitors will work and made in the values you need 12 mfd and 4 mfd. Now if they will fit on the board is another question. For cost they used polyester .01uf bypass. There is no 100 mfd cap what you are reading is the working voltage 100V.
Tolerance of 10% on their caps was standard the Solens are listed at 5% which is better in matching. Another L100T would be best for your center and use the L20T3’s for your rear or side fill. You might find just replacing the 12 mfd is all you need with a poly cap for an improvement.

 

[SaturationPt]

It’s a 40-year-old speaker, I’d be concerned with the suspension on the mid-woofer, and the damping in the HF driver, and the EL cap. The film caps are probably in fine condition. I have a few of the mid-woofer around here and the response from them can be wildly different as the suspension becomes much less compliant with age, as all butyl/rubber/poly surrounds do, and they’re much more difficult to replace (especially on a poly cone) than foam surrounds on pulp cones. The 035Tia foam isn’t too bad to service, be careful with the leads when unplugging however as the terminals do come loose.

Unfortunately drivers with “rubber” style surrounds are mostly not repairable and depending on the environment, no longer operating to spec after 10, 20, 30+ years and likely are trash. The T3 have the Tia tweeter and the tweeters are likely worth as much without the rest of the speaker, most of these are harvested for the 035Tia.

 

[Nostoppin1]

Hello and welcome, here is my take on your issue. First using the L20T3 as a center channel would not be the best fit sonically. In practice the center channel is usually matched to the Left and Right speakers in this case L100T’s. If you play it loud with movies or music the L20T3’s will come up short on output compared to the L100T’s. Your DCR values are OK as they are of an average value and the one reading high is not bad. The crossovers JBL made for them with cost considerations at the time. Solen capacitors will work and made in the values you need 12 mfd and 4 mfd. Now if they will fit on the board is another question. For cost they used polyester .01uf bypass. There is no 100 mfd cap what you are reading is the working voltage 100V.
Tolerance of 10% on their caps was standard the Solens are listed at 5% which is better in matching. Another L100T would be best for your center and use the L20T3’s for your rear or side fill. You might find just replacing the 12 mfd is all you need with a poly cap for an improvement.

wow, another L100T for a center channel? That blows my mind. I chose the T3's hoping that, being of the same era and series, they would match sonically. I'll give some thought to this!

So for the 4µF cap, any wisdom on what the CMC actually translates to?

 

[Nostoppin1]

It’s a 40-year-old speaker, I’d be concerned with the suspension on the mid-woofer, and the damping in the HF driver, and the EL cap. The film caps are probably in fine condition. I have a few of the mid-woofer around here and the response from them can be wildly different as the suspension becomes much less compliant with age, as all butyl/rubber/poly surrounds do, and they’re much more difficult to replace (especially on a poly cone) than foam surrounds on pulp cones. The 035Tia foam isn’t too bad to service, be careful with the leads when unplugging however as the terminals do come loose.

Unfortunately drivers with “rubber” style surrounds are mostly not repairable and depending on the environment, no longer operating to spec after 10, 20, 30+ years and likely are trash. The T3 have the Tia tweeter and the tweeters are likely worth as much without the rest of the speaker, most of these are harvested for the 035Tia.

Thank you

I've done the L100T's 035Tia foam, with my breath held hoping to avoid breaking them. I'll keep in mind the potential trashing of these L20T3's to sell for the HF driver.

What would you chose for a center chanel here?

 

[Chris Brown]

I don't think that the L20t3 is a horrible choice for a center channel, but it's not as good of a match to the L100T as you might expect despite being from a similar series. The only similar driver is the tweeter. The 035Ti in the L100T is crossed over at 4kHz. The 035TiA in the L20t3 is crossed over at 3kHz. A center channel speaker is all about vocals. The most important vocal frequencies are between 500Hz and 4kHz or so, which means the majority of the output from the center channel will be handled by a woofer (115H-1) that has many different characteristics compared to the 104H-2 midrange in the L100T. But that isn't to say that you shouldn't try it anyway, since you already have them. You would have to step-up to at least a L80T/L80t3 to get the 104H-2 midrange as the lower models are all 2-way.

 

[Nostoppin1]

I don't think that the L20t3 is a horrible choice for a center channel, but it's not as good of a match to the L100T as you might expect despite being from a similar series. The only similar driver is the tweeter. The The 035Ti in the L100T is crossed over at 4kHz. The 035TiA in the L20t3 is crossed over at 3kHz. A center channel speaker is all about vocals. The most important vocal frequencies are between 500Hz and 4kHz or so, which means the majority of the output from the center channel will be handled by a woofer (115H-1) that has many different characteristics compared to the 104H-2 midrange in the L100T. But that isn't to say that you shouldn't try it anyway, since you already have them. You would have to step-up to at least a L80T/L80t3 to get the 104H-2 midrange as the lower models are all 2-way.

Thank you Chris, I hadn’t thought things through and this makes perfect sense. That also explains some of the modern center channel speakers with multiple midrange drivers.

 

[bmnathe]

I'm also recapping my L20T3 (waiting for delivery of the 3.9uf caps) and chose a Clarity PUR for the 12uf and a Clarity CMR for the 4uf (3.9 replacement). The reason I'm recapping is that there is no measured capacitance for the 12uf on the right side and none for the 4uf on the left side. I think I had a power surge that killed the 12uf and took the woofer with it.

The curious thing about the Clarity PUR is that the leads are strands, which in total are a bigger gauge then the original (so they don't fit through the PCB). Instead of looping around to the backside of the PCB, I cut about half of the strands of each and fed them through the PCB - I think this is fine because it's relatively low voltage.

I should have everything received and assembled in a couple days - looking forward to it.