PDA

View Full Version : 1969 JBL C 70 Alpha 1 Crossover Help



thundermud
01-11-2013, 09:04 AM
Just picked these speakers up the other week and I am loving the sound, however I am wondering how much more I could be lovin the sound with a crossover restoration?I have re-capped crossovers before but not on ones like these. Also, the LPads make a little noise when I turn them, should I spray deoxit from the inside? Anyone have any suggestions on how to go about replacing the crossovers? Thanks!57921

Mr. Widget
01-13-2013, 01:56 PM
Not to be overly critical of your speakers, but the networks in them are particularly primitive. I am quite confident that a more advanced design could be beneficial. That said, it wouldn't be a trivial undertaking. I doubt that simply swapping caps would buy you much. Certainly if the L-pads are noisy, a bit of contact cleaner can't hurt.



Widget

thundermud
01-14-2013, 11:29 AM
Yes, they are shockingly primative! The speakers do sound very good at the moment but I would like them to sound their best. Do you know of anyone who could help build me a pair of crossover? Of course I would pay for their time, labor and shipping. I can not find any info/schemactics for these speakers. Thank you!

thundermud
01-14-2013, 12:04 PM
5793157932

JeffW
01-14-2013, 04:45 PM
And to muddy the water even further, read This Thread (http://www.audioheritage.org/vbulletin/showthread.php?23181-JBL-C70-Alpha-I-crossover).

Giskard says that LX30 schematic is for a different system, but posts links to a different LX30 network. Pretty confusing, but not surprising.

In particular, read posts #3 and #8, and the links #17 and #18 in post #3.

On the bright side, the LX30 Alpha 1 network couldn't be much simpler and doesn't need a tapped inductor. On the downside, it's pretty primitive as Widget mentions, and building a better mousetrap might be a long and painful road to follow.

thundermud
01-14-2013, 08:25 PM
Well then it seems I got my answer. I suspected this would be a lot more difficult than it's worth. I am happy with my speakers as they are. I really appreciate everyone's input, thanks again!

grumpy
01-14-2013, 09:50 PM
Thanks Jeff... I should have known better as the tapped inductor + LE20 should
have been a red flag that something was awry with that PDF. Glad you
found the reference to the earlier confusion.

JeffW
01-15-2013, 07:08 AM
Well then it seems I got my answer. I suspected this would be a lot more difficult than it's worth. I am happy with my speakers as they are. I really appreciate everyone's input, thanks again!

I think you just got spooked by the different LX30 tangents. IMHO, there can't be a much simpler 3-way crossover to build than the one for your system. You could keep the stock crossovers original and build up a pair of fresh ones for little of nothing if you just wanted to see how the speakers would sound with new components. The hard part would be designing and integrating a more complex crossover that would work with your drivers/cabinets. Keep it original design and it's not a big deal.

Take a look at the actual schematic:

thundermud
01-15-2013, 08:53 AM
I think you just got spooked by the different LX30 tangents. IMHO, there can't be a much simpler 3-way crossover to build than the one for your system. You could keep the stock crossovers original and build up a pair of fresh ones for little of nothing if you just wanted to see how the speakers would sound with new components. The hard part would be designing and integrating a more complex crossover that would work with your drivers/cabinets. Keep it original design and it's not a big deal.

Take a look at the actual schematic:


Crossover design is not my specialty but I feel like it makes sense to make a new 3 way crossover. I am not sure even if I had a more complex crossover made if it would be any better. I would like to keep the distinct sound of these speakers without overmodification, if that makes sense. Anyone willing to build me a 3-way crossover for me? Of course I would pay, just send me a message.

4313B
01-15-2013, 08:55 AM
Anyone willing to build me a 3-way crossover for me?They would have to have your loudspeakers to measure them before designing you a pair of networks. Anyone who tells you otherwise is just blowing smoke up your...

And maybe that's ok! I'm not going to judge. :rotfl:

thundermud
01-15-2013, 10:21 AM
They would have to have your loudspeakers to measure them before designing you a pair of networks. Anyone who tells you otherwise is just blowing smoke up your...

And maybe that's ok! I'm not going to judge. :rotfl:

Could I measure the speakers?

Mr. Widget
01-15-2013, 11:12 AM
Could I measure the speakers?You need test equipment... the Woofer tester is relatively inexpensive and will get you much of what you need. http://woofertester.com/


Widget

thundermud
01-17-2013, 03:10 PM
Hmmmm....does anyone live in NJ? I'd rather bring my speakers to someone.

Mr. Widget
01-17-2013, 09:27 PM
I'd suggest stop worrying about it and enjoy what you have. ;)


Widget

thundermud
01-18-2013, 06:23 PM
Not worrying at all? Just having fun. Thanks