Norman Lab Model 10 ~ Need Help Identifying Problem

[basicblues]

Just scored a pair of 1979 Norman Lab Model 10 speakers. One of them works great but the other plays but has a weak almost blown speaker sound. So I took both woofers out to test ohms which both tested good. Then I took a known good NL woofer spare that I had and hooked it up and it also produced same sound. Now I am thinking I may have a crossover issue. How do I test the crossover? or what would be the next step?

 

[lndm]

Try disconnecting the drivers and listen to them separately. The resistance measurements you performed suggest the woofers will work, but there may be a mechanical problem with them, also.

Once you know the drivers that are the problem, you can isolate the crossover components involved. You could put the driver in the other (good) cabinet or put the good driver in the bad cab. Then you should know if its the crossover or driver. Also, measuring resistance on the tweeters without the crossovers might make things easier.

In case you think this is risky, it isn't really. Keep the volume down all the same. Blown speakers (crossover shorts etc) can make amps unhappy, and blown caps can make tweeters unhappy. :thumbsdn:

 

[basicblues]

Thanks for the reply, I'll do some further testing to see if I can isolate the problem and post the results.

 

[beans]

I picked up a pair of Model Tens last night that have the polypro woofs. One of them has an issue apparently having to do with a circuit breaker. I noticed the one stopped playing at the same volume as the other so I checked the connections and tried pushing the reset buttons, which seemed to help.
Anyone else had this problem? I plan to try Deoxit on the resets before "going in".

 

[Westy56]

There is a good chance that the caps are bad. I think the ones that come with them are cheap ones from Mexico.(20uf 100v)?

Were you disappointed with the woofer basket build? I was.

Steve

 

[beans]

There is a good chance that the caps are bad. I think the ones that come with them are cheap ones from Mexico.(20uf 100v)?

Were you disappointed with the woofer basket build? I was.

Steve

I haven't removed any woofers yet, but I can see part of the basket through the cone, and they look kind of cheap-o... stamped metal I think.

So are you suggesting 20uF 100V, but better quality ones?

 

[Westy56]

I haven't removed any woofers yet, but I can see part of the basket through the cone, and they look kind of cheap-o... stamped metal I think.

So are you suggesting 20uF 100V, but better quality ones?

I am only to the point of disassembly.

There are 2 crossover caps from Mexico that are 20uF 100V.

There are also 3 (???) resistors (???) that are 2ohm 10% 5W.
Two of them are attached to the HF switch and one between the HF and one of the caps.

I can't make any qualified suggestions. I will be keeping my eye on this thread though.

Steve

 

[dan-c]

I haven't removed any woofers yet, but I can see part of the basket through the cone, and they look kind of cheap-o... stamped metal I think.

So are you suggesting 20uF 100V, but better quality ones?

What kinda woofs would you replace them with.

The more I read the more I'd like to rebuild the X-overs too. I guess I should wait until something happens but

 

[Phototone]

You should for sure replace all the caps. If you like, replace the resistors. If your X-overs have inductors, they usually don't go bad, or change over time, you can leave those alone.

 

[tensleep]

The poly woofers are actually very good quality woofers. I would hesitate to change them out without confirming they are shot. As far as the crossovers go, definitely recap. All of the circuit breakers can be bypassed as well when rebuilding. They are a good idea, but fuses would probably be simpler and more trouble free. There is also a circuit for attenuating the tweeters. This complication could also be eliminated with a fixed value circuit or possibly an lpad. I have studied my crossover, but have not modified it yet. Maybe it's time to get with it while so many other AKers are working on theirs. We can compare notes as we progress!