[shipsupt]

Bias was 588V!?  So higher than pro-bias?  I guess we're safe then to try the Kingsounds from any pro-bias amps.
 
I wonder if I should take a bias measurement on the tube amp?  If the specs are that far off from what you measured, I wonder if there is any consistency between amps?

 

[kevin gilmore]

here is a close up.
http://gilmore.chem.northwestern.edu/m10-1.jpg
and I measured it this morning with my 6.5 digit lab grade instrument just
to make sure.
The top line between R203 and R242 is the main B+ and is regulated 588V
goes first to R108 which is 1.8 meg
then to R141 which is 1.5 meg then to
R142 which is 1.8 meg then to
C122 which is .01uf and then to
the headphone jack.  Which is 5.1 megohm from 588V
 
removing R108 and moving it to R110,R111,R140 would change the bias voltage.
(463,346,229)
 
The person that measured the bias voltage on the tube amp probably measured from the wrong
place.

 

[shipsupt]

Not sure if someone else measured the bias voltage on the tube amp, but I gave Spritzer the B+ voltage from the tube amp as 585V.  Is the B+ going to be the same as the bias voltage?

 

[kevin gilmore]

need to trace the bias wire back to the power supply. if its the same cap and resistor directly to
the supply then its the same voltage. or measure with a dvm with known impedance and
calculate the real voltage that way. usually dvm's that are not damaged are 10M impedance.

 

[kiertijai]

Bias was 588V!?  So higher than pro-bias?  I guess we're safe then to try the Kingsounds from any pro-bias amps.
     Can we make a conclusion now that we can use the Kingsound with the pro-bias stax amplifier?  (If it can be driven
by DIY T2 safely)
 

 

[kiertijai]

Please also compare to 507 and Koss ESP950

 

[spritzer]

The amp circuit from the first pictures appears to be a Stax SRM-1 Mk1/SRA-12S circuit almost part for part.  Not a bad piece of kit in 1972 but now... you can so much better.  The PCB will get very, very hot as it acts as the heatsink for the output devices which is not a good idea. 
 
Quote:

Not sure if someone else measured the bias voltage on the tube amp, but I gave Spritzer the B+ voltage from the tube amp as 585V.  Is the B+ going to be the same as the bias voltage?

 
The bias supply is a voltage divider but I can't see where it gets the raw DC from.  If you look at where the bias wire is terminated, look just a bit to the right (in the pic you sent me) and there is a via going to the other side of the board.  That feeds the voltage divider. 
 
The bias supplies in these amps appear to be clones of old Stax ones and aren't really compatible with the newer models from Stax despite the voltage used. 

 

[spritzer]

So here is the "final" schematic of the M-10:
 
http://gilmore.chem.northwestern.edu/m10.pdf
 
Compare to Stax from 1972... 
 
http://i.imgur.com/Ua44Us1.jpg
 
Now the active components are naturally different but it is very, very similar. 

 

[MacedonianHero]

Quote:

The amp circuit from the first pictures appears to be a Stax SRM-1 Mk1/SRA-12S circuit almost part for part.  Not a bad piece of kit in 1972 but now... you can so much better.  The PCB will get very, very hot as it acts as the heatsink for the output devices which is not a good idea. 
 
 

 
Exactly, definitely not a good thing for thermal cycling the amp. The hotter it gets it expands more in the Z direction (and I seriously doubt that they're using low Z pre-preg...typically used for aerospace/MIL only). So this will only stress the plated through holes and wear them out sooner than later.

 

[kevin gilmore]

There is just so much fail in the solid state amp. Taking a 40 year old stax design, swaping the output bipolar out
for a mosfet and then surface mounting everything with modern construction techniques, such a waste of time.
more than 40 degrees phase shift at 100hz relative to 1khz. All the bass boost (which makes it even worse)
is not going to fix that issue. At least they could have taken the srm252 design and done the mosfet outputs
to that. Would have been much better. Like another has done.
 
The headphones on the other hand, I kind of like. Reminds me of sr3 physically. But not built as well.
Sound quality on par with cheaper stax, and esp950. Slightly different presentation.
 
But when you compare $, not really a bargain as a system.
 
usa price with amp  $1k  more with the tube amp
stax 2170 price $850, price from japan $550
esp950 price $650 to $800
 
So buy the headphones definitely for $500 and hook them up to your favorite stax amp.

 

[analogsurviver]

Quote:

There is just so much fail in the solid state amp. Taking a 40 year old stax design, swaping the output bipolar out
for a mosfet and then surface mounting everything with modern construction techniques, such a waste of time.
more than 40 degrees phase shift at 100hz relative to 1khz. All the bass boost (which makes it even worse)
is not going to fix that issue. At least they could have taken the srm252 design and done the mosfet outputs
to that. Would have been much better. Like another has done.
 
The headphones on the other hand, I kind of like. Reminds me of sr3 physically. But not built as well.
Sound quality on par with cheaper stax, and esp950. Slightly different presentation.
 
But when you compare $, not really a bargain as a system.
 
usa price with amp  $1k  more with the tube amp
stax 2170 price $850, price from japan $550
esp950 price $650 to $800
 
So buy the headphones definitely for $500 and hook them up to your favorite stax amp.

ESL amps are forgotten/overlooked/misunderstood species. There are TONS of useful info in Heymeyer and Sanders' series on ESL amps originally published in The Audio Amateur and later reprinted in Speaker Builder magazines. Stax ESL amps, although decent, are far from the end of the road. From your description, King Sound version is even much less than that.
 
ESL amps are the most expensive thing to make right - as they simply force you to use whatever best you can  possibly lay your hands on - and even then it is just barely enough. Try real x00 V/uSec rise/fall time - with load attached. Getting decent phase response in the low frequencies is a simple matter of either DC ( heroic, potentially dangerous if any insulation fail ) or AC ( large(r) value high quality caps , $$$ ) coupling - far easier than getting the same in the treble, where only prodigious and unfortunately lethal amounts of voltage AND current will do the trick. That is why Stax (and most other ESL amps ) are specified with frequency response from X to Y Hertz at much lower level than full output - they can not output full level at the upper extreme, even not under severe distortion. And I have yet to see published phase shift for an ESL amp driving its intended load in the treble... - essentially, it is the thing one is paying for, just listen to the difference with say SRM 252 and any "full size" Stax model. 
 
It would take an amp of infinite power to allow for 0 degree phase shift in the treble under capacitive load - an obvious impossibility. Back when MOS FET output power transistors came out, their essentially capacitive inputs had to be first equalized for capacitance ( P and N types have meaningful difference in input capacitance ), then usually a much lower resistance was used in parallel to that input capacitance, so that over bandwidth of interest input of this "composite MOS FET" behaved essentially as resistor ( offering no or very low phase shift ) - BUT it required driver that was essentially lower powered power amplifier ( approx 20 or so W ) to drive the output devices properly.
 
No such thing as free lunch - but King Sound amp as described does not seem to justify the price.

 

[spritzer]

For 300$ this amp was not worth it, for 500$... ehh go buy something else. 

 

[Miracles]

So I just went to Moon-Audio's page to look at the specs again and I found that the price for the headphones are now $625. Add solid state amp total is still $1000, so I guess only difference is that if you buy the cans by itself its now $125 more. Considering the initial impressions it looks like a cheap Stax might be a better option so far.

 

[spritzer]

Just got my KingSound setup and the phones work just fine off Stax Pro bias.  The M-10 data sheet clearly says bias of 580V and the headphone leaflet (well card) says they were designed for "Professional" amps and the M-10 and M-20 are optional extras. 
 
As for the sound, early impressions are not promising.  This is off a KGSSHV...

 

[MacedonianHero]

Quote:

Just got my KingSound setup and the phones work just fine off Stax Pro bias.  The M-10 data sheet clearly says bias of 580V and the headphone leaflet (well card) says they were designed for "Professional" amps and the M-10 and M-20 are optional extras. 
 
As for the sound, early impressions are not promising.  This is off a KGSSHV...

Interesting Birgir...I didn't think one could run these off a Stax pro bias? Well, the KGSSHV is definitely not limiting these headphones that's for sure. Looking forward to more impressions.