[jamato8]

Quote:

Originally Posted by bangraman Just curious to see if there have been any updates for this.

The latest word that I heard from Jan Meier is that the channel imbalance issue was located by Sennheiser, and can be repaired. It's not an amp issue at all. The later batches of the new HE90's already have the fix in place. If you've got one of the earlier new production HE90's and it has a channel imbalance issue with Stax amps, the fix can be applied. I do not know any details of exactly what is done to correct the issue. If your HE90 has no problems out of a Stax amp, you do not need to have anything done.

"If your HE90 has no problems out of a Stax amp, you do not need to have anything done."

Very old but not sure what this means. The Bias for the HE90 is 500 volts so what is being done here?

 

[Hirsch]

Basically, the 580 volt bias out of a Stax amp could cause the stator to stick to the membrane. In some of the then new construction HE90's, a small spacer (micron or two) was left out, reducing the gap between the stator and the membrane. No problem with 500 v bias, but a problem with the higher Stax bias voltage. Restoration of the spacer created sufficient distance between the stators and the membrane so that the headphone was no longer sensitive to the increase in bias voltage when a Stax amp was used.