A S.E.X. for Stax. Putting the E back in sEx :)

[xcortes]

Awesome,

Now, can you tell us why you chose th 507s? I've never heard electrostatic amps but based on my experience with the Quad esl I want to try a pair.

PJ, could this experiment be done with a Mainline? Thanks

[johnsonad]

IMHO, all headphones have a slightly different flavor and the 507's worked best for my wife and myself (I dragged her up to listen to them).  I spent a couple of days at the 5555 headphone shop in Tokyo before leaving Japan listening to all of the current line of Stax earspeakers and their amps.  The 507's beat out the 407's, 307's and Omega II's on Stax amps in sound.  The 009's sounded better to my ears than the 507's but are very expensive.  Given you can find Stax for half the listed American price in Japan, it was a no brainer. 

I hope to find a pair of Sigma Pro's and maybe a pair of 4070's someday. 

There is probably a Stax dealer around you somewhere Xavier. You would need to track down the importer to find the dealers through.

[HF9]

Hi Aaron, I was wondering if you might be able to go into a little more detail about how the specially modified Crack lines up against other Stax amplifiers. I was hoping you might be able to compare it to the Cavalli eXstata if you've happened to hear it.

Regarding the hum, I thought you might be having some magnetic flux issues as the outputs are so close to the power transformer, but it sounds like you got that squared away.

Great work, by the way!

[FraGGleR]

This is too cool.  I like the aesthetic decisions as well. 

Do you mind sharing the total cost of this amp project with us? 

[HF9]

Do you mind sharing the total cost of this amp project with us?

I looked up the iron and it would be over $500 USD to have a pair of the Sowter OPTs (non-custom) shipped to the U.S, shipping was about $85 pounds 
I think the Spritzer board runs about $60 last time I checked

[FraGGleR]

Do you mind sharing the total cost of this amp project with us?

I looked up the iron and it would be over $500 USD to have a pair of the Sowter OPTs (non-custom) shipped to the U.S, shipping was about $85 pounds 
I think the Spritzer board runs about $60 last time I checked

Oof.  Thanks for posting that.

[johnsonad]

At HF9, my sonic memory isn't the best so unless they were all side by side I woudn't want to say how different it sounds from the current Stax offerings.  I did compare it against my power amp to the Stax SRD-7 transformer box tonight and the S.E.X. still has some break it ahead of it.  I don't think this project is going to be the end all be all of Stax amps but does offer something a little different.  I'm still happy with how it sounds but it isn't there yet after only 24 hours of burn in.  I may roll some caps in the future to fine tune the sound.

The transformers were originally intended for the new SR45 design and still may move over to that amp when it is released.

At Fraggler, HF9 has it pretty close on cost.  They were not cheap.  There is no extra charge for the zero gap version. If I end up finding a better amp to try them in then the S.E.X. will go stock form. 

[johnsonad]

48 hours of burn in and the sound is improving.  My biggest grip is with the highs and upper midrange. After doing some reading it seems Jon L ran into the same thing with the Audio Cap Theta's and bypassed them with Russian FT-1 Teflon caps.  I ordered a few today and will report back as to how it makes an improvement.  I'm considering using the ClarityCap MR series if the bypass doesn't give me the top end I'm looking for. 

Tonight I listened to Bat For Lashes, The Haunted Man and Junior Boys, Begone Dull Care through this combo and both CD's sounded nice. This is very easy to listen to for extended periods of time.

[tdogzthmn]

any new updates on your project?  I've been looking into a 507 or vintage Omega for myself and wondering if a converted Bottlehead amp will be the route I take.  Maybe a modded mainline will yield better results.

[Doc B.]

I think I might take a very different approach to an ESL headphone amp than modifying one of our existing designs. I'd have to do some calcs, but I should think the power bandwidth of something as small as a headphone panel wouldn't require much current. I'm thinking like a voltage quadrupler for volts and maybe like some 6BK4s for drive.

[johnsonad]

Four days of break in and it's opening up nicely. It's very easy to listen to and has about as much top end as I would want. Transients and "air" could be a little better (but not much better) and I hope the  FT-1 bypass caps will take care of that. I also ordered a pair of 18uF ClarityCap SA for the power supply.

I've owned a dozen high end pairs of headphones but got out of the revolving cycles a few years back. This is the first combo I've enjoyed for extended periods since my first combo (WA6/HD650) in 2006.  I nit pick the details but I'm very happy with this combo and will continue to make small tweaks.

@Dan, PB had another design in mind using EF86's. I went with the S.E.X. because I needed something....... It would be cool if you guys could come up with a kit for the Stax crowd at some point. If you can afford Stax you can afford a nice kit  

[tdogzthmn]

That would be awesome Doc! Of course an circuit optimized for ESL headphones would be the ideal route but I have no expertise in designing electronics.  If you and PB were able to cook up something im sure there would be interest here and on headfi.

[johnsonad]

I put in a pair of MQ high nickel grid chokes tonight. Zero hum or noise pick up (lucky!). Listening impressions tomorrow.

[johnsonad]

So grid chokes, from reading through past posts I was very worried about noise and hum pickup but in the S.E.X. they are quite easy to place.  In my case I just super glued them to the plate chokes centering and lining up the laminations.  In a standard S.E.X. they would mount on the OPT as an option.

Sound wise they increase resolution.  Like getting a new prescription from your optometrist, you didn't realize things were a little fuzzy around the edges until you get the new glasses.  The grid chokes are the new glasses.  Decay, note sustain and air sound more realistic.  They don't make a huge difference but they do make a difference for the better.

This still has a way to go. My SS amp and speakers continue to sound better than the S.E.X./Stax combo.

[johnsonad]

Rio (my wife) and I were having issues with the sound today going back in forth between the speakers and headphones. Voices were great but piano in the 300-500Hz range was off as were strings in the upper range.  As I'm waiting on caps to roll anyway I swapped the 0.47uF Audio Caps for the 1uF Auricaps. This made a large improvement in the overall sound. I never thought cap rolling could be fun until now