srx revisited

[mypasswordis]

Sorrodje/Ali-Pacha, I don't think anyone would mind if you posted some updated measurements in the Stax thread here.  Tyll only has a couple Stax measurements up on Innerfidelity, and some of us are big fans of vintage Stax. 

[Ali-Pacha]

@Jim L I don't have SR-L700, but you're right on the 10 staxens collection, which is barely acceptable for someone posting down there...hey, I'm no 007mk1 lover and don't have any clue in electronics, so be gentle.

Not so much to add to @Sorrodje's impressions. I could have written exactly the same statement on amp's ranking on HE60, as well as how far modded 727 stands from the two other contenders of the day.

My opinion is a little bit different for 009, as I would insert two or three more ">" between BHSE and SRX+. No mystery I'm 009 lover, HD800 are probably my favorite non stat, but my tastes aren't exactly the same as Sorrodje's, so I value a bit more kick in the low-end, control, amount of details and soundstage provided by the BHSE's. Q/P ratio remains always on the cheaper one, don't mistake me, worn-out diminishing returns platitude in audio.

SRX+ is not as "right" as BHSE, but there's something very funny and energetic in its presentation. Think about the low-medium kick and foot tapping thing you can get from SRD-7 + good ol' 2-channels amp, but with detail retrieval and soundstage you have on a very good dedicated amp, way way above modded 727 level even if some steps under BHSE's. When listening to 009 on SRX+, I was thinking about my Lambda Signature on steroids, kinda vintage sound, with 009 details and technicality (and Sorrodje loves Lambda Signature )

007 are another story, as my main concern with them is their lack of dynamic compared to what I like. BHSE raises them at pretty good level at last, but on the same amp, they can't compete with my other Staxen's regarding dynamics IMO (main exception : Lambda Nova Signature). So the transformer-like sound exhibited by SRX+ (again, with details and soundstage from top notch dedicated amp) may be my choice to get the best experience with those unloved ones.

Ali

 

Edited January 17, 2017 by Ali-Pacha

[blubliss]

On 1/16/2017 at 8:35 PM, JimL said:

blubliss, I thought you had a SinglePower ES-1 that had been modified to work properly?

I have an ES-2 which does work and has been modified but not in the manner presented here. The thing is it just sits unused.  I even offered it to someone for free pickup and he never came.

[Jon L]

On 1/16/2017 at 0:50 PM, Sorrodje said:

 

 

 

I bought a quad or french NOS Laradiotechnique 12AT7 and a pair of NOS GE but replaced it lately by a pair of 6SNGTB Chrome top Sylvanias and they improved the sound ( tighter , clearer , more transparent) significantly .  

Summary for HE60 : BHSE >>> SRX+ >>>>>>>>> 727. if the HE60 was my main headphone, I'd order a BHSE right now.

Good pairing but not as special as the HE60/BHSE one to my ears.

Surprise came from the SRX+ there... Honestly I think I'd choose the SRX+ over the BHSE for the 009, especially if I wanted to use a 009 on daily basis 'd see the ranking as this : BHSE>SRX+>>>>>>>>>>>>> 727 . the experience made me want a 009 to associate to my SRX+ ...more than a BHSE

 

Interesting read, as I own 009 and HE60, and I fully empathize that one amp that sounds "right" with one 'phone will sound suboptimal with the other 'phone.

As I stare at my big box of 6SN7 tubes, I can't help but sigh at the fact SRX+ uses 6SN7 GTA/B, which I have never found to sound as satisfying as the better 6SN7 tubes.  As I also stare at my big box of 12AT7's and another box of 12AX7 tubes, kind of wish SRX+ was in front of me to tube roll 'til cows come home, but oh, well..

[JimL]

Actually, you could run 6SN7GTs in the SRX Plus, you just need to cut down the voltage to, say +/-250 volts for B+ and cut down the output standing current to 6mA per section.  You would lose about 3 dB in ultimate loudness but if you listen at reasonable levels that shouldn't be too much of a problem.

[JimL]

There were a few reasons for using 6SN7GTA/GTB output tubes rather than 6SN7GTs.  First, a higher voltage and power rating, which means that  we are working in a more linear part of the tube curves, second, there are new tubes available for those who don't wish to mess with NOS,  third, the original GT tubes actually have lower voltage and power ratings than the 6CG7/6FQ7 tubes specified in the original SRX design, and fourth, NOS GTA/B tubes are still reasonably priced, whereas some 6SN7GT tubes are going for silly money these days.

Edited January 20, 2017 by JimL

[luca]

Hello Jim,

I'm building your own version of SRX amplifier and your shunt regulator PSU. Before ordering the transformer I would be sure of the necessary AC voltage.

On the shunt pcb there is AC700 CT

If VDC = VAC x 1.41

350-0-350VAC = 490-0-490VDC and if the shunt drop 20VDC I think the voltage is too high.

Then the transformer should be 260-0-260VAC, correct? (200mA be enough?)

Another question: how do I adjust the CCS shunt 10M90S-DN2540? What should I read on the 10ohm test resistor? 0.4V? 0.5V?

Thank you

[JimL]

The voltage depends on whether you use a choke input or capacitor input.  Basically, any transformer that would work for a KGST would work for the SRX Plus using a cap input filter.  If you use a capacitor input filter then the voltage is higher than needed - although remember unless you have a regulated AC line, the voltage may drop 10-20% in the summer with all the air conditioners, etc, so you need to allow for that.  When you do that, then the DC output from the cap filter could be 20% low, which would decrease it to around +/-390 volts.  In that case, if you are allowing for worst case 20% low, 700 volts would be ample.  On the other hand, if you are only allowing for 10% low AC line, then 600-650 VCT would probably work.  I haven't checked recently to see what is recommended for the KGST but it would work equally well for for the SRX Plus, since both can run on +/-350 VDC.

 

If you use a choke input filter, the voltage would actually be less than the AC voltage, e.g. around +/-330-340 volts, so that 800V-850CT would be a better bet.  On my build, the transformer was specified at 780VCT and I had to decrease the PS output voltages to around +/-315 volts to get enough headroom for regulation.

 

For the shunt PS, I would set the shunt so the 10 ohm test resistor has about 0.43-0.45 volts across it.  Remember that my most recent revision of the PS has moved the capacitor at the 431 regulator from between the reference terminal and ground, to between the reference terminal and cathode.  That is not reflected in the PS circuit board so you'll have to cut a couple of traces and solder new ones to the back side. 

[luca]

Thanks, Jim

 

I built this with the recent updates that you posted.

 

for this power supply what is the voltage that the transformer must have?

[JimL]

If you are using the on-board rectifier diodes on the PS board, you can use the same transformer as a KGST - same voltage, a bit less current needed.

 

On the other hand if you built a  choke input power supply as in my original schematic (P. 4 of this thread, posted 9/16/16, 3rd from the bottom) , which means the rectifiers are off-board running into a choke input, and the output from the chokes goes to the PS board, you will need 800-850VCT - I know my schematic shows 780VCT but that is actually too low.

Edited February 11, 2017 by JimL