[Currawong]

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This sounds like an excellent idea. The SR009 is comparatively very sensitive (feels louder) than my Omega 2mk1 at the same volume level and, as you mention, the O2mk1 sounds better at higher volume levels. I wonder then if having the O2mk1 plugged into the high bias and 009 plugged into the low bias would yield similar loudness (in the rare case where I listen with my wife or if were to use a realiser for movies playback through the phones).
 
Apart from the drop in gain (6dB?), any other drawbacks?
 
Anyhow, Justin, would that even be possible for me to consider (in place of the 2 pro bias stax plugs currently) at this stage of the build? Maybe two pro bias plugs but a different bias setting on each output? (In my case, I don't foresee using normal bias phones, or I'd simply look for a used T1 just for that).

 
yes, i can still do it.  this is probably the last batch where i will be able to.  too many combinations of jacks/colors/volume controls means i cant have someone else do that part of repetitive assembly without mistakes

 
Would have differing bias levels affect the performance at all? Or would it effect the same thing as having different gain on each socket?

 

[padam]

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Would have differing bias levels affect the performance at all? Or would it effect the same thing as having different gain on each socket?

Yes it does, reduced bass output and dynamics is what I noticed so in almost every case it is the native bias which is recommended to be used (e.g. from what I've read it is not a good idea to run a HE90 at 580V Pro bias instead of 500V).

 

[spritzer]

The HE90 is a special case as it is far more fragile than any Stax driver.  Sennheiser clearly state the max input voltage the headphones can handle but Stax would never publish that, simply no need for the Pro models. 
 
The bias sets the potential of the diaphragm or how much "grip" the drive voltages will have over it.  Since the grip is also tied to the D/S gap a Pro set used at normal bias sounds softer with less dynamic range.  The volume is effected but not nearly as much as a change in gain. 

 

[satorarepotenet]

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The bias sets the potential of the diaphragm or how much "grip" the drive voltages will have over it.  Since the grip is also tied to the D/S gap a Pro set used at normal bias sounds softer with less dynamic range.  The volume is effected but not nearly as much as a change in gain. 

Thank you Spritzer.
 
But I am still confused! Doesn't it make sense to ask Justin to change anything on the BHSE for the few times one wants to use the 009 and the 007 at the same time? Does the BHSE come usually with normal or with high bias?
 
Last question, which one is better (normal or high bias) when we leave aside the question of using two headphones at the same time? Is is true for 009 and for the 007?
 
Justin, do you have any recommendation? Should I just stick with the standard BHSE and deal with the small difference of volume (009 vs 007 for the times I used them together)? 
 
Many thanks.

 

[Asr]

^ I'd guess that if you don't specify which jacks you want, Justin would probably configure your BHSE with 2 Stax Pro jacks. You should use the SR-009 on a Pro jack. Just because it can work on a Normal jack doesn't mean you should use it that way.
 
If you have no plans to ever acquire Normal-bias headphones, then you should get 2 Stax Pro jacks for the reason that spritzer mentioned. Normal-bias jacks simply add the functionality so that 6-pin headphones like the old SR-X MKIII and SR-Lambda can be used with the BHSE. You shouldn't try to use Normal jacks as a "pseudo-Pro reduced-gain" type jack. They're specifically for driving 6-pin Stax, not 5-pin Stax.
 
Btw, for anyone else thinking about using Pro/Normal for the SR-009 and OII for simultaneous listening, it would actually make more sense to put the SR-009 on Pro and the OII on Normal, since the Normal jack has higher gain than the Pro. In other words, don't think of Normal bias as "low" and Pro as "high", because the Normal bias jack has a high gain compared to the Pro! In fact, if you theoretically plugged two OIIs into a Pro/Normal BHSE, the OII on the Normal jack would sound a fair bit louder than the one on Pro! When I mentioned reduced gain, I meant that only for the Pro jack, NOT as a reason to use the Normal jack for anything (other than 6-pin Stax, that is).
 
Perhaps this clarifies the result a little better: a Pro/Normal BHSE essentially turns the Pro jack into a low-gain jack and the Normal jack into a higher-gain one, as far as 5-pin Stax are concerned. Use the Pro for all 5-pin Stax and the Normal for all 6-pin. Again, I never said to use the Normal jack to drive either the SR-009 or OII - and if that's the idea that certain people got, then that was the wrong idea.
 
And for anyone wondering, yes I tried the config when I temporarily had the OII MKI and SR-009 simultaneously not too long ago.

 

[satorarepotenet]

^ Thank you for the clarification. -- Did you notice a big difference in volume when you tried the 007 and the 009 for simultaneous listening? Would you say that the difference is manageable, assuming that someone likes to listen at a slightly higher volume than the other person, or that it would be quite problematic (even for a couple of hours per week of listening with my wife)? 

 

[padam]

I think the volume difference significant - but you can always get a Lambda for secondary use (like the SR-407), which should be close enough.

 

[satorarepotenet]

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I think the volume difference significant - but you can always get a Lambda for secondary use (like the SR-407), which should be close enough.

Yeah, people seem to have different opinions about that. I am curious to find out what ASR thinks about that (from “barely audible” to “quite significant”).
 
Of course I am aware of that possibility (a pair of Lambda), but when someone mentioned the possibility of having a high and standard bias I thought that maybe it would solve the problem without me having to buy new headphones. 

 

[arnaud]

Thanks all for the comments, I think it's a case closed for me: two pro-bias plugs for me. Anyhow, I realized that the only chance I'd share the listening would be watching movies with my wife, but then I'd most likely invest in a realizer and would need to use two amps for two individual PRIR/HPEQ sets... 
 
Only potential thing: Justin, there is no way to set a different gain settings on both outputs? I thing it's no issue for me since I won't be using a stepper and the RK-50 apparently is great even at very low volume settings. But since I listen to fairly mild volume levels (esp. the 009), I wonder if having less gain (like 6dB) on one of the plugs would maybe be useful (also when I have both the O2mk1 and SR009 plugged).
 
Arnaud

 

[justin w.]

that is impossible as there is only one amplifier

 

[arnaud]

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that is impossible as there is only one amplifier

 
Ok, case closed then

 

[struggles]

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Ok, case closed then

 
Closed for me as well, 2 pro bias jacks it is. Thanks to all for the questions and answers on this. Think I have everything ironed out now, though fantasies do pop up every once in a while that are not silver...but then I get scared and goto the comfort zone.

 

[satorarepotenet]

Case closed here as well! Thank you all. 

 

[n3rdling]

Pro/Normal is where it's at.  It opens up the ability to listen to some pretty special headphones (SR-Lambda/SR-Sigma), as well as the old cheaper Stax stuff (SR-5/SR-Gamma/etc).  It's also more future proof: what if a manufacturer decides to get into stats and their headphones require a lower bias?  The normal bias jack would likely come in handy.

 

[arnaud]

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Pro/Normal is where it's at.  It opens up the ability to listen to some pretty special headphones (SR-Lambda/SR-Sigma), as well as the old cheaper Stax stuff (SR-5/SR-Gamma/etc).  It's also more future proof: what if a manufacturer decides to get into stats and their headphones require a lower bias?  The normal bias jack would likely come in handy.

I'd probably be happy driving a normal bias phone with a T1 and really only have the BHSE in mind for my O2 and 009. As for future proof, what if sennheiser actually go ahead and release a new totl stat product. Somehow, I feel chances it would share even just the bias with stax phones are slim. So, no need to think so much forward imo.
 
In any case, many thanks to all for the comments, it helps to figure these things out. Just need to wait for the spring / summer and and the good things that come with it .