Gentlemen,
and now a nice little repair story and a testament of STAX build quality - or rather the lack of...
I have a pair of lambda pros which I got off german ebay along with an SRD-7 mk2 some time ago. Unfortunately they had quite a bit of channel imbalance - it could still be fixed with some balance adjustment but the right earspeaker was significantly too low and also slightly distorted and I had very rare cases of no sound at all after hours of listening which took some time powered off to fix.
Not too bad, they were very cheap... that's what I thought..
Today I decided to have a look into the SRD-7 mk2... and this is what I found:
So obviously STAX decided to solder the zener diodes ZL01-ZL04 from the schematics found here
http://www.head-fi.org/t/589430/lightbox/post/8038174/id/490157
directly to the pro bias jack 8-O
But it gets better... closer inspection showed that the contact for the pro bias (grey wire on bottom) was almost touching a piece of wire standing over from one of the right channel contacts and did actually make contact with some light tapping (or possibly by the unit getting warmer after some hours). I corrected this with wire cutters and some careful bending.
After reassembly the channel imbalance was still there but then I applied what had helped temporarily before - slight tapping of the right system made me dash for the balance pot to set it to neutral. Unplugging the phones and uncharging the bias (breath on your fingers to slightly moisten and touch contacts of the phone plug - no worry, doesn't hurt) and replugging showed the channel balance was still good...
So I guess the channel imbalance was caused by one of the right side leads occasionally shorting to the pro bias and partially fusing the diaphragm to one of the stators. Tapping the affected speaker managed to get the diaphragm free and with the short circuit removed it hopefully won't get stuck again...
Lessons leaned:
- If your energizer is acting funny, having a closer look on the jack contacts might be a good idea... BUT REMEMBER TO UNPLUG IT FIRST - LINE VOLTAGE IN THERE CAN KILL YOU!
- If your stax speakers show channel imbalance slight tapping of the low system might help... if the diaphragm is just stuck and not perforated.
Joachim