[alwayshungry]

I just wanted to update this thread for completeness. I have been really busy moving but have been meaning to update this thread. 
STAX finished the repair of my SR-009s in about 3 weeks. They said that there wasn't any problem over the phone (I can't read the repair paperwork as it is all in Japanese) but they did burn in the SR-009s for 2 weeks straight.
 
I am not experiencing any channel imbalance problem through the same setup nor through a SRD-7 PRO energizer. The serial number is the same.
 
I am sure that when I sent them in that I was a channel imbalance but unfortunately I did not get a chance for anyone else to help me verify. They sound absolutely perfect now with no signs of imbalance or decreased response in either channel. When I got them back I burned them in for another 40+ hours or so continuously.
 
One of the benefits I had is that they sealed everything back in their packaging that I sent and it was like opening a brand new pair. Anyone that has unboxed a pair of these knows the obsessive attention to detail that is spent on even the most minute details of the packaging. 
 
I did not mean to cause panic and I hope that nobody else experiences this issue in the future.

 

[CybDev]

Thanks for the update alwayshungry

Oh, and mine are still working perfectly

 

[Shep]

Sad to report my SR-009 have developed this imbalance.  Been getting worse for 2 months, now R is -7dB.  SN 1773.  Will keep you posted.

 

[CybDev]

Ouch... sorry to hear that

Mine is still working perfectly

 

[spritzer]

Going by the pile of PM's I keep getting about the imbalance it is a real problem and Stax haven't solved it.  Now all electrostatic headphones can develop an imbalance due to a parasitic charge on the diaphragm but this doesn't appear to be the case with the 009.  Two reasons, the imbalance can be changed with outside influence and it is way too common.  Doesn't appear to be any easy solution to fix this but I haven't received a busted set to try out yet. 

 

[CybDev]

Haha, I get so nervous every time I see a new post to this thread
I keep hoping someone will say they solved it before the 19xx run
Just hoping mine won't develop the imbalance issue... that would suck something awfull

 

[eric65]

Hello,
 
In France, two problems of imbalance L/R (> 15 dB) recently found for Stax headphones : for a 507 (mine : immediate default) and a 009 (one of Pierre : default after 30 hours of listening).
 
For now my 009 works well.
 
Eric

 

[spritzer]

A brand new set from Japan went bad recently so it hasn't been fixed.  It's definitely a connection issue but where it is, that's the problem. 

 

[CybDev]

Come to think of it, my SRM-323S does have two separate volume controls, one for each channel.
I can't remember if the other stax amps have a similar function, but the volume knob was of the same type iirc...
Perhaps intended to compensate for the imbalance issue?

 

[spritzer]

All Stax amps (save for the small ones) have had this since the early 70's.  It's to adjust for small differences in sensitivity between the left and right ears, not the channel imbalance in the transducers. 

 

[arnaud]

I finally took some time to measure my Omega 2mk1 yesterday and also re-measured the 009 to check for consistency / repeatibility. While I didn't notice anything last time, it would appear the right channel of the 009 is 1-2dB down from the left side. The omega 2 seems just fine and I could reproduce the imbalance using different measurement method (on urethane backed plate or using in ear microphones).

So, while I haven't processed the data yet (just was looking at the time traces / peak meter in audacity), it would seem my 009 has also gone south a little. Will report back after I get done with the number crunching.

 

[arnaud]

False alarm... No channel imbalance with my 009 after all. I double checked the RMS levels with Audacity, no issue.
 
- Here's a new measurement of the 009, repeted 3 times, could be cleaner but not terrible:
 

 
- On the other hand, the miniature in-ear mics are a real letdown, what a pair matching and SNR below 50Hz... This post is going to be forwarded to tech support soon...

 

 
- Here is a comparison of SR009 measurement (on a urethane lined plane baffle using EMC8000 mic): yesterday vs. last august. I believe the differences at high frequency is more due to mic placement (else the amplifier has totally different transfer characteristics as a function of volume - I do not test at specific SPL - yet):
 

 
Arnaud

 

[spritzer]

That's with the 727?  Then volume is an issue given the non-NFB design and lack of power to pull it off properly. 

 

[arnaud]

Hi birgir,

Yes, that's off the stock 727A... I wondered why Tyll didn't include measurements when he did his recent comparison of different amps.

I will probably try to repeat the measurements at different volume levels, using a sound level meter to calibrate it (for instance 60-100dBA by 20dB step).

 

[spritzer]

Because it is very hard to measure electrostatic amps. 

  Tyll's test equipment can't do it so he needs highly specialized tools just for this.  Then there is the issue of what to test, personally I'd echo my advice to Tyll when he was doing the review and torture the amps to their limits.  That's how Stereophile tests normal amps, utterly to the limit and they have had failures on the test bench.