The Stax thread (New) - Page 50

The transformers in the SRD-7 have a turns ratio of 24:1 and the Lundahl transformers have a 14.4:1 turns ratio. A 300 watt (into 8 ohms) amp is developing about 50 volts across the load. Just multiply the turns ratio by the voltage and you get the output voltage to the stats. In either case the voltage is higher than any SRM made by Stax. It would be LOUD and possibbly enough to arc the stat elements (I do not know the arc voltage of the O2). The transformers would be over their watt rating and overheat also. I would think 75 to 100 watts (rated into 8 ohms) would be plenty with either trans.

AudioD

I don't know of anyone who's compared them directly side by side. I own the O2s and Carl owns the 4070s and recently we did a week long swap but of course that means neither had both on hand at any one time to compare directly. A benefit though is that we did get to use them with our own systems eliminating most other possible points of difference that would trouble a comparison.

In my opinion the decision should come down to how much isolation you require, the 4070s isolate more in both directions. They'll bother other's less and you will be bothered less by external noise. Both headphones are great once they've got a good charge but I did find I had to put the volume higher for the 4070s for them to really do the trick. The level of refinement of both is very high.

Which did I prefer and why? To me the O2 has superior frontal headstage and imaging which I suspect is due to the large round driver and shape of the pads. The 4070 headstage sounded more two dimensional extending out around the ears but very little seemed to come from in front of my face the way the O2s manage. I also find the O2 a little better at dynamics. There were times I was just wanting the 4070 to deliver just that little extra oomph for me to be 100% happy. What I'm talking about are those moments when you're really into the song and you're thinking "Oh, I love the bit coming up next" but when it got there it was just a little less magical than you were expecting. When I say a little less I really mean a little. It was clearly noticeable to me but a small difference all the same. I think it's best said in the form that the O2 has superior dynamic resolution but the 4070 is definitely in the same ball park. There are differences in the frequency response too and which you prefer will come down to taste. I believe the metaphor Carl used was that the 4070 was a little "flat chested" in comparison which sits well with me. I think this is where the "good for monitoring" aspect of the 4070 comes in but anyone thinking the 4070 is not musical would be mistaken. Indeed the 4070 is very enjoyable to listen to.

I'd like to stress again though that these points of difference are by and large small, I certainly don't want to exaggerate them so that people think these are vastly different headphones in completely different leagues. Both have a similar character and level of refinement. To my ears neither have significant weaknesses but I do find the O2 has the edge, especially given my tastes in presentation. This is why in my opinion the need for isolation is the main factor I would use to guide a buying decision between these two.

I can't comment at all on the R10 as I've never heard it.

Welcome to the light, that's why I sold my Stax amps, even the ancient and lowly SRD6 sounds awesome through a decent amp. Or even a really cheap decent amp in my case. I love the t-amps with the SR-X

You can just use the schematic above and skip the transformer. It's not recommended but Stax all other makers of electrostatic headphones didn't use a transformer for the bias supply. This doesn't apply to the self biased types but they are driven of the audio trafos secondary.

Thanks for your impressions; it looks like only you and Carl have done some kind of meaningful comparison between the two. Isolation is not really a factor for me, since I have my own room.

I will now wait for Carl to chime in

With all this talk about output voltages I put together the following list. If some amp is missing it's because I couldn't find the right specs. All voltages are RMS

Stax
SRA-3s 270v
SRA-8s 350v
SRA-12S 350V
SRA-14S 400V

SRM-1 370v
SRM-1 Mk2 370v
SRM-3 300v
SRM-T1 300v
SRM-X 270v
SRM-T1S 300v
SRM-T1W 300v
SRM-T2 630v
SRM-Xh 280v

SRM-212 280v
SRM-252II 280v
SRM-310 350v
SRM-313 350v
SRM-323II 400v
SRM-717 450v
SRM-727II 450v
SRM-006t 300v
SRM-006tII 300v
SRM-007t 340v
SRM-007tII 340v

WooAudio
GES 420v

Rudistor
Entire line of amps 250v(*)

Headamp
KGSS 495v
Blue Hawaii 565v
Aristaeus 425v

Sennheiser
HEV70 425v
HEV90 400v

Koss
E/90 600v

Singlepower
ES1 w/EL34 output tubes 565v

(*) The specs Rudistor has on his page are plainly wrong. The Standard Egmont is rated at 630v the same as the SRM-T2 with a 6SN7 output tube.

I see that Spritzer is an advocate of running these from a tranformer and large power amp. This may work, but I don't like tying up an amp that way. You would need to connect your speakers to the terminals on the transformer and that is not going to be good for the speakers.

I have just been listening to Sigma pros through a SRM-3, amp, the precursor of the current 313 and it is pretty effective. I would pay attention to power however, since these phones are less efficient than the Lambdas with which they were later replaced with by Stax. Some fairly cheap tweaks to get more power from your amps are: 1) use an upgraded power cord; 2) plug the amp directly into the wall, rather than use a power strip for them; 3) use a contact enhancer on all plugs, pin and IC's. I have used Progold over the years but am now more impressed by Mapleshades' Silclear, a silver-based product.

The STax 717 is significantly more powerful than the SRM-3 or 313 but also a lot more expensive. There are numerous other aftermarket amps now available.

spritzer,
Great List! Thanks.

AudioD

That's good info, thanks! From what I hear, arcing the stat elements IS a potential concern with the OIIs. The thing about big amps is, I believe, dynamic headroom. No doubt, you could hit 300 or more watts with a sharp peak under certain conditions, but, like a high-powered auto engine, you don't HAVE TO use all the HP/potential. Most audio amplifier just sound better when they have some breathing room at the top that is rarely, if ever, tapped.
Anyway, the formula indicates a potential swing of well over +- 1KV, plenty, I would say. And, using the 14:1 turns ratios would seem to keep things a bit safer, while reducing system efficiency.
Thanks!

If you look at the schematic for the SRD-7 Pro it has protection on the low voltage side to protect the transformers and some on the HV side to protect the stats. They are devices that should not hurt sound quality. They should be incorporated into any new design if you plan to push the envelope.

AudioD

That's quite a different perspective from where I was coming from focusing on different aspects and by and large I agree completely. Hopefully together they will give humanflyz a good feel for the differences between these two. The reproduction of timbre for vocals and individual instruments is very impressive on the 4070. Very clean and very real. I loved some of the Jazz I listened to on the 4070, made me wish I had more. Beautiful for double bass. I also agree that the O2s are also not a perfect fit with electronica and pop but when provided with enough voltage swing, the powerful dynamics can compensate to a certain degree, and a little EQ can take it even further. I listen to quite a bit of electronica and pop myself so it was important to me to get this right. I have found when I've got my pre-amp, amp and EQ set just right I'll even enjoy pop/electronica I wouldn't normally go near such as the Pussycat Dolls album PCD.

You and Carl both provided some very good information, but it hasn't helped me decide lol, which is a good thing I guess: more choices. I would've been happy with an O2+KGSS combo since I've heard that combo before and like it. But you know what they say: can't leave well enough alone, just had to be curious about the 4070, which receives very very little attention. But it seems to be picking up, as I've heard from both you and Carl, Gordie, and Wmcmanus have chimed in. What piqued my curiosity was that Gordie, who is a big fan of the K1000s, likes them a lot. And Wmcmanus wrote last night that in some areas, the 4070s might even have an edge over the Orpheus.

So Rudistor's stax amp should be quite ideal to drive the O2s? But they don't seemed to be favoured. I wonder why? Their amps do look gorgeous albeit not as compared to the ES-1 IMHO

Wow,the numbers are much lower than expected. I guess that I (and possibly others) were thinking the numbers on the KGSS(700v), KGBH(800v), ES-1(800v) ,etc WERE the RMS values. Are you sure the STAX amps are truely rated with the RMS value ??