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EDIT: Bad pot made me think my 077s were distorting

Johnny_Law

Johnny_Law

o.O
Subscriber
EDIT:

It was one of my mid pots. I had it sitting on a dead spot. I thought it was the tweeters!

ORIGINAL POST:

My 077s are distorting. They have the original blue diaphragms.

Is this a common failure symptom of bad original diaphragms? Or some other cause? Or is this unusual?

Here's a video ... you can hear distortion when the treble comes in. I've swapped in my Thiels and the distortion on the same song is totally gone (so it's for sure not the source / pre-amp / amp / anything else causing it).

The song is "Black Coffee" by Delacey if you could please compare to your own setup, so you can hear the difference to my 077s which are distorting / ringing / sounding horrible.

 
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Both at once? I don’t believe in coincidences, has something happened to them recently or has something changed? Have you checked the trimpots?
 
It's my first time really listening to them - they've got a questionable history and were in horrible shape when I got them. Wouldn't shock me if both went bad some time before I got them.

I noticed the right one over the last couple days ... and chalked it up to bad recording, my bad hearing, etc.

Today the left one started doing it too. That got me curious enough to make a recording of the sound, and swap in the Thiels. The Thiels don't have any issues at all.

So unfortunately yes, both are doing it.

Background: I just barely started listening to the L300s. I've had them for a while but was busy restoring the cabinets. During the restoration, I cleaned all four pots and measured the resistance sweeps, all good. I also swapped the woofers and LE85s into and out of my old L200Bs to make sure they are good; and, they are. I measured the DCR of the 077s and both measured OK, but I didn't have any way to test them before I had the L300s back together. Something sounded off from day 1 - it's just now I'm putting my finger on it.
 
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Are the Mids OK? Highly unlikly they would both go bad. were they previously ok?
 
If I were you I would pull them out, check the readings, see if you can find a 1 or 1.5 uf Capaciter to play them directly. low power only, and listen to it.
 
I cant tell from the playback
but my experience with Tweeters, horn drivers, is that when one goes bad they just quit! I never heard a JBL 075,6 or 07 play with distortion. they would just Quit
Im thinking either a bad conection could be corosion or something with the xovers
 
Relative to my L200/300 with 2405s, it sounds like you have no highs, or even upper mids for that matter. I have seen "shattered" diaphragms with pieces broken out of them from abuse.

How about a different recording with more duration? Something that has some cymbols in it.
 
Thanks! Have any suggestions - a song you know well?

(The recording is only as good as my Pixel 2 cell phone...)
 
I suspect they may need to be disassembled, and the magnet gaps (where the voice coil fits into) cleaned out with compressed air and sticky tape in the gap.

A bit of rust, dust or other particles in there, can make tweeters sound quite raucous, sometimes. And, with the age of these- if they haven't been cleaned, there could be all sorts of errant stuff in there, that's collected over the ages...

Regards,
Gordon.
 
I had a beater pair of L300’s a few years ago with similar issues. Most of my issues were the stinkin’ L-pads. When I took them apart, I saw the coils were corroded. I sprayed the crap out of them with contact cleaner and scrubbed them with a brass brush. That cured the problem for me. Unfortunately, you have to remove the foilcal, sucks, to get to at least one of the screws.
 
Johnny, did you ever figure out what's going on with your 077's? easy enough to unscrew the horns from the cabinets, and pull them, check the back to be sure they have not had the foilcals disturbed, then unscrew the mounting plate and horn, noting the orientation. Then you can see the diaphagrm and phase plug and inspect for grit, grime, and other debris on the outside of the ring diaphragm. Look closely at the connections to be sure they are not corroded. DO NOT BRING ANYTHING METALLIC CLOSE TO THE DIAPHRAGM as the magnet can pull it in and destroy the diaphragm. If they still don't reveal your troubles, then ship them to Edgewound at Upland Loudspeaker or Bao at Speaker Repair Pros in Garden Grove for servicing.

Otherwise, investigate the L-Pads again as Jenkster did or replace them with new from Parts Express, same with the speaker wire, contacts and connections to the crossover. Use DeOxit D5 plus Gold after cleaning. You may also consider replacing the caps and resistor in the HF crossover section.

https://manuals.harman.com/JBL/HOM/Technical Sheet/L300 Summit ts.pdf
 
Even when a 077 is working properly they sound harsh and are very irritating. But imagine what you are hearing is failure do to the caps changing in the crossover which could also allow the ringed diaphragms to be compromised. If the adhesive has failed causing the issue only replacements will correct part of the issue. You still need to rebuild the crossovers or the problem will return quickly. Even then I would look for the 2405 replacement tweeters with a much smoother and lower distortion type sound.
 
twiiii said:
Even when a 077 is working properly they sound harsh and are very irritating. But imagine what you are hearing is failure do to the caps changing in the crossover which could also allow the ringed diaphragms to be compromised. If the adhesive has failed causing the issue only replacements will correct part of the issue. You still need to rebuild the crossovers or the problem will return quickly. Even then I would look for the 2405 replacement tweeters with a much smoother and lower distortion type sound.
Click to expand...

So what makes it harsh and irritating, the lucite center vs aluminum or the blue diaphragm? I've not heard a difference, aren't they the same design and same specs other than impedance?
 
Thank for all the comments. I haven't had the time lately to get these back into the garage, or even listen to them, so they remain a mystery. Really appreciate all the discussion.

The L-Pads have already been removed and cleaned thoroughly (and resistance-checked to confirm they work correctly).
 
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twiiii said:
Even when a 077 is working properly they sound harsh and are very irritating. But imagine what you are hearing is failure do to the caps changing in the crossover which could also allow the ringed diaphragms to be compromised. If the adhesive has failed causing the issue only replacements will correct part of the issue. You still need to rebuild the crossovers or the problem will return quickly. Even then I would look for the 2405 replacement tweeters with a much smoother and lower distortion type sound.
Click to expand...

Do the N333 caps generally go bad? I have debated re-capping, but after a ton of searching didn't find many / any discussions talking about out-of-spec caps in these networks. Are they electrolytic in there?
 
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