Need help fixing broken rheostat in JBL 3114a crossover network in a 1973 JBL 4315A

[JBL Nicholas]

Hey everyone,

I have been restoring a pair of JBL 4315A speakers... I have finished all the work on the driver's and electronics and had them fired up for an hour of testing.

They sounded amazing... For one hour :(

I need to replace the rheostat that controls the attenuation of the 8" JBL 2108A driver.

Please help me out with advice guys! Thank You!
70361

[Doctor_Electron]

https://www.google.com/search?q=61594+l+pad&ie=UTF-8&sa=Search&channel=fe&client=browser-ubuntu&hl=en&gws_rd=ssl#channel=fe&hl=en&q=61594+l+pad+16+ohms

Wow, 4315's. I would "drool" over them in the Warehouse Sound catalogs (San Luis Obispo, CA) back in the mid seventies. You have a worthy project, best of fortunes with it.

Regards, "dOc"

[300_Summit]

You can get new L-pads from parts express. I believe the 16 ohm L-pads come in 3/8" shafts. You'll need 1" shafts. So what you'll have to do is by the 8 ohm L-pads (with the 1" shaft) and swap them to the 16 ohm L-pad. There is actually a detailed thread showing this. Do a search on L-pad and you'll find it. But it's pretty straight forward.

[JBL Nicholas]

Thanks guys! Now I just need to figure out how to rewire the crossover network to allow for biamping... Any ideas?

[300_Summit]

Thanks guys! Now I just need to figure out how to rewire the crossover network to allow for biamping... Any ideas?


Do a search within this forum. I'm sure there is info out there on that particular subject.

[mech986]

the control in question is actually part number 51594, not 61594. It is a common part used also in the JBL L300 / 4331 / 4333 midrange crossovers, and likely with the 434x midrange or 2420 upper mid.

You might call JBL Professional and see if they still have it available (just checked - none) or check Ebay for the controls, however, those would be used and old. the PE new units would be your best choice in new products.

[grumpy]

Thanks guys! Now I just need to figure out how to rewire the crossover network to allow for biamping... Any ideas?

2nd set of terminals direct to LF

Might need to put in a resistor where I've shown a short to emulate
the impedance of the 52uF/2.2mF at the crossover freq (say 4-8 ohms)
so the remaining filter response doesn't change shape much. In that case,
disconnect at least one lead of the 52uF cap.

It's just a starting point... and only one of several ways to "bi-amp".

What I've shown assumes a 12 dB/oct electrical crossover prior to the amps.
If you use a different slope, you'll likely need to connect the LF
out of phase vs what's shown in the schematic.


70400

You -could- just run four amp channels and leave -all- the passive filters in,
just separating the LF filter input from the rest and bringing the leads out
to an additional pair of terminals. Simpler, if not better (and less destructive).

Have fun.