JBL 123A-3 distortion @ volume

[slowburn]

I use a pair of 123As in my own vented boxes crossed via autoformers and caps to LE85s on 400hz Le Cleac'h horns and JBL 2405s rolling in above 12k. Recently, while blasting something, I detected some horrible distortion. Traced to one 123A, it only breaks up when turned up loud. It sounds fine at lower (normal?) volume. Power is via HK Citation 2, completely rebuilt, triode strapped KT88s, very clean sounding. What are best guesses as to what's wrong with this driver? Original cones and surrounds in fine shape. Might it be something as simple as having become demagnetized? Or has something failed utterly? Thanks!

[badman]

You could be exceeding Xmax, or the coil could be misaligned (or worse, coming loose from the former)

First thing first, try rotating the mounting of said driver 180 degrees then see if it persists- don't keep pushing it, just test to see if it still distorts, then back it off.

[fpitas]

Not sure if this is applicable to the 123A-3, but I remember a thread where the spider was coming unglued from the frame. You might take a look. The fix seemed easy, simply gluing the spider back down.

Francis