The Stax Thread III
Aug 22, 2014 at 7:11 AM Post #2,971 of 25,421
+1. Which is when Geoff stepped in.......

True. And hats off to Kevin G for his wisdom and generousity to the DIY community. I wonder if Stax have 'given up' the desire to market a Stat amp that aligns with their 007 and 009s? Even the lower models sound MUCH better when driven well by a BHSE or KGSShv. I have not heard the Woo Audio amps or the Eddie Current, but would bet they do the same as well.
Maybe Stax is still a small niche company who make probably the worlds best headphones. There are high end speaker manufacturers who don't make amplifiers, and who demo their gear with amps they deem having some synergy with their gear. I would think the market size for the 007s and 009s isn't big enough for Stax to survive, and they have to sell a 'system' with the headphones to be attractive to the general public.
It is interesting, that even with their IMO poor attempts at amplifiers, their headphone systems still sell well against none stats. It shows just how good the electrostatic headphones really are IMO.
Aug 22, 2014 at 8:24 AM Post #2,973 of 25,421
Just recently you were confused over the topology of the BH

Ehh? The BH is a KG amplifier, seems not relevant here. You know, you don't NEED to know the technicalities of this or that amplifier if you rate them with your ears.
The Stax 717 was not so bad an amp, but the cost v performance is not so good IMO. Better can be had IMO by going DIY or other none Stax amp routes. I spent 20 years 'stopping' at the SRM-313. I had to dig around the forums to realise there were other alternatives, and that is what makes these forums and this hobby so good.
Aug 22, 2014 at 9:39 AM Post #2,974 of 25,421
What is so fundamentally wrong with the topology of modern Stax amplifiers excepting non-NFB (727) and unregulated power supplies (virtually everything else)?

I would agree they are overpriced, but I think the same for all electrostatic driver units, first-party or third-party -- be it overhead, base cost of the BOM or some combination of the two.
Aug 22, 2014 at 11:01 AM Post #2,975 of 25,421
nothing wrong with the topology of current stax amps, and the 727 can be fixed and pretty easy too.
The issue with unreg power supplies is that of size. Cramming a fully regulated supply inside the
same size box is a big problem. And the extra heat is a problem too. Much easier to put big
external heatsinks on the box instead of inside the box.
Aug 23, 2014 at 6:52 PM Post #2,976 of 25,421
Hello to everyone!
Sorry for the stupid and probably frequently asked questions. 
For now I used dynamic and planar-magnetic headphones, and have interest in electrostats. 
Currently I have Hifiman HE-400 on Schiit Modi+Magni, followed by Beyerdynamic T1 on Bottlehead Crack OTL. 
I was thinking about Stax 2170 system, or 3170 as comparable headphones in price. 
Would it be step up, or something else?
Aug 24, 2014 at 3:38 AM Post #2,978 of 25,421
  I was thinking about Stax 2170 system, or 3170 as comparable headphones in price. 
Would it be step up, or something else?

I think better if you buy SR-407 and SRM-323. I have this system and it sounds good. But sometimes all stax phones needs a little bass boost at equalizer (I'm using foobar2000). I cannot recommend you 2170 system and 006 amp.
Aug 24, 2014 at 3:52 AM Post #2,979 of 25,421
  Hi Kevin,
How do we quantify the performance of an electrostat amplifier? What unit of measurement should be used?
Also, as it is a seeming consensus that the SR-007 has greater amplification requirements, how do we measure this? It specifies the same 100dB / 100V r.m.s. 1 kHz and a lower capacitance relative to other models.

You don't need to measure it to be convinced, us your ears. Anyone who has heard the 007s against the 009s and even the 507s will hear it needs more current to sing. The design of the drivers in the 007 was the first real attempt IMHO where Stax addressed the 'rest of the world' taste for some real bass, as apposed to transparency only. Maybe this was partly why it needed more current? The 007s is a great headphone, it was possibly a problem for Stax that none of their amplifiers available to the real public (no T2) was really capable of doing it any justice. 

Electrostats aren't like dynamic headphones - amp current capability has nothing to do with bass - only Vswing does
  Electrostats do react differently to increased current than the expectation formed from experience with dynamic transducers
Bass doesn't require current to speak of in ES headphones - for electrostats more current increases slew rate - ability to push high V amplitude at high frequency - not Bass
+/- 1mA output will drive 100 pF ES headphones to the amp's +/-500 V supply limits @1 kHz, requiring proportionally less current as frequency descends to any approximation of Bass
the vast majority of music has been found to have <~3kHz "power bandwidth", a good thing with SE 5mA biased output ES headphone amps being common

Aug 24, 2014 at 8:51 AM Post #2,980 of 25,421
Thank you jcx.
Would the ideal measurement be V/us @ 100 pF 20 kHz?
Is it possible to calculate the peak linear SPL of these amplifiers using their stated maximum output voltage @ 1 kHz?
Aug 24, 2014 at 12:56 PM Post #2,981 of 25,421
depends on your goal - its a signal you wouldn't want to listen to
but it would separate out some ES amps from others
that's the point of my music "power bandwidth" comment - above ~3kHz (~highest fundamental of  acoustic tonal musical instruments) the signal level in most music drops faster than the frequency rises, meaning the signal slew rate doesn't get any higher
even percussion is somewhat rounded, seldom has full amplitude and instant rise time - but that is where you would listen for a difference in ES amps vs output current capability
outputs that run at only a small fraction of their bias current can be more linear - another good reason for higher operating current than the minimum demanded by music averages
but whether you can hear differences in ES amps nonlinear distortion below slew limiting, clipping is not a simple 1:1 function of output bias current
Aug 24, 2014 at 3:05 PM Post #2,982 of 25,421
Got my SRM-727A for a while now, just wonder what is the "fix" on the 727 all about?
Aug 25, 2014 at 3:52 AM Post #2,985 of 25,421
Follow Arnaud, Frenchman in Tokyo, who has regular contacts with Stax :
On a french forum, he said Stax frozes amp's developpment because far too expensive for the SQ improvement.
To be continued...


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