The Stax Thread III

[eric65]

  Hello everyone,
 
Always, for information.
 
SRM T2 amp listening seems to be improving "hot".
 
 
 
 

 

 

 

 

 
Here an direct comparison for SRM T2 Vs SRM 727 on 009 and an indirect comparison for SRM T2, Vs SRM 727 Vs RKV-WEE on 009 (with not shunted and shunted Wee transformers)
 
See links (in french)
(you can use google translator)
 
http://www.homecinema-fr.com/forum/post177810847.html#p177810847
 
http://www.homecinema-fr.com/forum/post177811772.html#p177811772
 
PS : It used SRM T2 is currently for sale in France
 
http://www.casques-headphones.com/les-bonnes-affaires/381-stax-srm-t2.html#

 
Amp SRM T2 sold this morning (at a Polish)

 

[spritzer]

The pots on the SRM-600 are correctly labeled so standard T1 biasing setup is all you need.  In the T1 the labels for the pots are reversed but the part numbers are correct:
 

 
This one has been changed to ECC99's but here it is quite clear that the balance and offset labels are wrong. 
 
The offset being at -70V makes no sense though after the amp has turned off.  The tubes have stopped conducting but if the anode resistors are shot then  that might account for it while the caps discharge. 
 
Quote:

  I have a modded SRM-600 Limited and think it sounds wonderful.  Some shots of the interior.
 

 

 

 
I'm so going to save these pics.  I love these utterly clueless mods which cost a pile and just degrade the perfomance.  Seriously, who thought it was a good idea to side mount the caps that are supposed to be close to the circuit? 

 

[realmassy]

^ yeah but the green is so nice -

 

[Pier Paolo]

Yes, 4 of the 8 the plate (anode) resistors were broken: 2 for each channel: 50%, like the statistic. I have measured them and 4 (2for each channel) were 29,5K but one was 1000k an three were 600-900k. So, I have bought 16 new standard resistors 15K/2watt/5% (the 30k ones are very difficult to find here) and next sunday I will mount then in series at the place of the old ones. I hope that this would be enough. Do you think that 2Watth and 5% would be fine?

 

[kevin gilmore]

That will be fine but the resistors should be non-inductive film resistors
For best performance

 

[tdogzthmn]

I can't comment on why he modded it in this fashion, I know he's not totally unfamiliar with energizer schematics but I can testify that I works and sounds fantastic with my SR-507.  Very clean and neutral without fatigue during extended listening sessions.  

 

[RedBull]

I'm so going to save these pics.  I love these utterly clueless mods which cost a pile and just degrade the perfomance.  Seriously, who thought it was a good idea to side mount the caps that are supposed to be close to the circuit? 

It looks that the 'hulk' caps are too tall to be soldered vertically?

 

[DefQon]

^ yeah but the green is so nice -

It's all about the green....except mine ain't as bad as that one and only rebuilt the sections of the amp that needed as spritzer likes to put it 'some TLC'.
 

 
I have a handful of these Russian K42Y-2 0.022uf 1kv caps and enjoyed having them in some of my other amps so why not, replaced the old ceramics that were in there. My mind might be playing tricks on me but the amp sounds brilliant with the SR-5's, the K42Y rolls off the upper registers just enough to tame some of the bright end treble of the SR-5, sounds bloody brilliant, enjoy this combo more so than anything else I've heard or owned.
 

 
BTW, does anybody here know what these particular 60's diode are called? (Definitely not selenium or germanium, early based silicon?)
 

 

[complin]

There must be something wrong with your T2 as it is by far the best Stax amp bar none! 
It must need a service or some refurbishment. It won't sound its best until it has warmed up so 30 minutes minimum an hour even better.
 
I have had all the Stax amps vintage and new stuff and the only ones that come close to the original T2 are IMO Kevin Gilmores' designs.  The BHSE or the DIY T2.  I can't comment on the Electra as never heard one 
 
Quote:

   
So swapping the tubes helped a bit...
Just guessing here, replacing all of the old capacitors and a general "tune-up" would help as well.
Curious how the T2 performed with the Omegas?

 

[spritzer]

Yes, 4 of the 8 the plate (anode) resistors were broken: 2 for each channel: 50%, like the statistic. I have measured them and 4 (2for each channel) were 29,5K but one was 1000k an three were 600-900k. So, I have bought 16 new standard resistors 15K/2watt/5% (the 30k ones are very difficult to find here) and next sunday I will mount then in series at the place of the old ones. I hope that this would be enough. Do you think that 2Watth and 5% would be fine?

 
To echo what Kevin said, stay with either metal or carbon film.  Vishay makes some excellent 2W metal films and the Koa SPR2 carbon film units I use are also great. 
 

  I can't comment on why he modded it in this fashion, I know he's not totally unfamiliar with energizer schematics but I can testify that I works and sounds fantastic with my SR-507.  Very clean and neutral without fatigue during extended listening sessions.  

 
It's quite clear that the person who did this has no clue what so ever as to what the parts do and why they are there.  Measure this monstrosity against the stock amp and it will be far worse, there is no doubt about that. 
 

  BTW, does anybody here know what these particular 60's diode are called? (Definitely not selenium or germanium, early based silicon?)
 

 
"Silicon Diode-1"  :-D
 

 

There must be something wrong with your T2 as it is by far the best Stax amp bar none! 
It must need a service or some refurbishment. It won't sound its best until it has warmed up so 30 minutes minimum an hour even better.
 
I have had all the Stax amps vintage and new stuff and the only ones that come close to the original T2 are IMO Kevin Gilmores' designs.  The BHSE or the DIY T2.  I can't comment on the Electra as never heard one 

 
No chance a stock T2 sounds even close to spec after all this time.  The caps are all perished and it needs to be adjusted up to spec again.  Filament transformer is probably on its last legs too as they will all fail in the T2. 
 
Also T2 with the stock tubes...  wow they are bad. 

 

[Pier Paolo]

Hi Spitz, I have bought 16x15 kohm, 5watts, 2% non inductive carbon film resistor made in japan (i could not find the 30k and the 2w was only 14). Now I cant recall the brand, but it is the same light green that you used to upgrade a T1 to a 600ltd (i have read your posts). Tonight I will operate and install them. I hope this (and biasing) will solve.

 

[DefQon]

Hi Spitz, I have bought 16x15 kohm, 5watts, 2% non inductive carbon film resistor made in japan (i could not find the 30k and the 2w was only 14). Now I cant recall the brand, but it is the same light green that you used to upgrade a T1 to a 600ltd (i have read your posts). Tonight I will operate and install them. I hope this (and biasing) will solve.

Kiwame? They are also green and made in Japan, great resistors.

 

[Pier Paolo]

Yes, Kiwame. I have changed them tonight. Mounted in series 8 X (15k +15k).
Now I can set both DC balance and DC OFFSET NEAR TO ZERO (0,2-0,4 mV both and both channels), finally. After two hours the values were stable. The sound is perfect, all the distortion is gone. WOW!
The only thing that I can't understand is that I can measure near to 25 V offset also after having turned off the unit AND also unplugged. My friend said that it is normal because of the capacitors... Tomorrow I will check again after 12 hours unplugged. It is strange that STAX has not inserted a resistor to discharge the capacitors after switched off.

 

[DefQon]

I don't think bleeder resistors are required to negate/discharge the capacitors after power off in Stax amplifiers.

 

[Pier Paolo]

After 12 hours unplugged, DC offset is still +32V. Then I have measured the resistors again (unit off for 12 housr, without tubes) and the value is 28,8 kohm for each couple of two nominally 15kohm solded in series. After that I have plugged the ampli an measured again DC Balance and Offset: values ok and stable..