[WilCox]

Stax specs their amps at rms volts and Justin specs his at peak volts. So, for an SRM-007 at 350 Vrms your would get about 480 V peak if you want to compare apples and apples.  I would like to audition a higher power Stax amp, but frankly, my 717 and 007 suit me just fine driving my O2s and are better than any dynamic rig I have ever heard.  I don't listen at high volumes so peak power is not an issue with me.  Other improvements in audio quality might be interesting though.
 
 

 

[WilCox]

 
Quote:

@ WilCox - where did you come up with that? Sumpin aint right...
 
Also FYI, HeadAmp's KGSS has 350V rail to rail, so 700V RMS swing. BHSE - 400V rails / 800V RMS swing, IIRC.

Here's from Justin's website on the KGSS:
 
[size=x-small]SPECIFICATIONS[/size]
 

[size=xx-small]Device Type[/size]	[size=xx-small]Solid State (JFET, Bi-Polar Transistors)[/size]
[size=xx-small]Frequency Response[/size]	[size=xx-small]5Hz-45KHz +/-0.1dB[/size]
[size=xx-small]Signal-to-Noise Ratio[/size]	[size=xx-small]inaudible[/size]
[size=xx-small]Total Harmonic Distortion[/size]	[size=xx-small]<0.008%[/size]
[size=xx-small]Gain[/size]	[size=xx-small]1000x / 60dB[/size]
[size=xx-small]Input Impedance[/size]	[size=xx-small]50K ohms[/size]
[size=xx-small]Output Voltage[/size]	[size=xx-small]1200 Volts peak to peak[/size]
[size=xx-small]Inputs/Outputs[/size]	[size=xx-small]1 XLR input, 1 RCA input, 1 Stax Pro-bias output[/size]
[size=xx-small]Bias Voltage[/size]	[size=xx-small]580VDC (adjustable)[/size]
[size=xx-small]Operating Voltage[/size]	[size=xx-small]100VAC, 120VAC, or 230VAC[/size]
[size=xx-small]Power Consumption[/size]	[size=xx-small]80 Watts[/size]
[size=xx-small]Chassis Dimensions[/size]	[size=xx-small]16.5 (L) x 16.0 (W) x 4.0 (H) inches[/size]
[size=xx-small]Weight[/size]	[size=xx-small]18lb / 8.0kg [/size]

 

 

[deadlylover]

The KGSS should be able to swing 1400V p-p with it's 350V rails, but it doesn't, so he rates it honestly at 1200V p-p.
 
The Stax amp at 350Vrms rated output will be swinging nearly 1000V p-p.
 
My head hurts again.....

 

[El_Doug]

from what I understand, it depends on how you bias the output device   the rails simply dictate the maximum potential voltage swing
 
Quote:

The KGSS should be able to swing 1400V p-p with it's 350V rails, but it doesn't, so he rates it honestly at 1200V p-p.
 
The Stax amp at 350Vrms rated output will be swinging nearly 1000V p-p.
 
My head hurts again.....

 

 

[deadlylover]

Quote:

from what I understand, it depends on how you bias the output device   the rails simply dictate the maximum potential voltage swing

I don't think you can swing higher than what the rail voltages allow, Justin is awsum so he takes into account some headroom.
 
ninjaedit: Yeah I'm agreeing with you =P, I forgot to add that it also depends on the circuits losses and any tiny DC offset. I *think* biasing the output device sets how much standing current you want at the ready, I'm unsure how it will affect the voltage swing apart from how linear the output devices will behave.

 

[livewire]

Quote:

 

Here's from Justin's website on the KGSS:
 
[size=x-small]SPECIFICATIONS[/size]
 

[size=xx-small]Device Type[/size]	[size=xx-small]Solid State (JFET, Bi-Polar Transistors)[/size]
[size=xx-small]Frequency Response[/size]	[size=xx-small]5Hz-45KHz +/-0.1dB[/size]
[size=xx-small]Signal-to-Noise Ratio[/size]	[size=xx-small]inaudible[/size]
[size=xx-small]Total Harmonic Distortion[/size]	[size=xx-small]<0.008%[/size]
[size=xx-small]Gain[/size]	[size=xx-small]1000x / 60dB[/size]
[size=xx-small]Input Impedance[/size]	[size=xx-small]50K ohms[/size]
[size=xx-small]Output Voltage[/size]	[size=xx-small]1200 Volts peak to peak[/size]
[size=xx-small]Inputs/Outputs[/size]	[size=xx-small]1 XLR input, 1 RCA input, 1 Stax Pro-bias output[/size]
[size=xx-small]Bias Voltage[/size]	[size=xx-small]580VDC (adjustable)[/size]
[size=xx-small]Operating Voltage[/size]	[size=xx-small]100VAC, 120VAC, or 230VAC[/size]
[size=xx-small]Power Consumption[/size]	[size=xx-small]80 Watts[/size]
[size=xx-small]Chassis Dimensions[/size]	[size=xx-small]16.5 (L) x 16.0 (W) x 4.0 (H) inches[/size]
[size=xx-small]Weight[/size]	[size=xx-small]18lb / 8.0kg [/size]

 

I knew you were gonna post that worthless p-p spec from his site.
Looks good on paper to woo the masses...
The RMS  "rail" voltage is what does the "heavy lifting" (work).
Have you ever seen the inside of a KGSS?
The power supply board outputs are clearly labeled 350V.
 
 

 

[milosz]

Quote:

So, can anyone tell me why there are 2 headphones in in the Stax 007tII amp when it is designed to be paired with the higher-end Stax phones which are power hungry and need all the power of the amp (and some here say that its not even enough to drive one pair of 007's, incl. me).  I understand in some of the other Stax amps one out is normal and the other is pro, but here we have 2 pro outs!  This is the 3rd time i've posted this but no response.... it probably is a very stupid question!

Stax headphones are not power hungry.  In fact, they use almost NO power.  They want VOLTAGE SWING, which is NOT the same as power.
 
You can plug in 2 Lambdas, it works OK.  Stax headphones don't really use any current.... just voltage. Two sets of Lambdas won't load it down, really.  (or 407's 0r 507's etc)
 
And 2 sets or SR-007's will work about as well as one set; which is to say, you get sound but really they need more voltage swing  than the usual Stax boxes can provide.
 
Voltage is not the same as power.  With dynamic headphones, they actually consume power - with Stax headphones, they want voltage but use hardly any current.  That's the same as saying they don't really consume much power.  So adding a second set does not significantly load the amplifier down.  Voltage swing with a single Lambda Pro from an SRM-T1  is virtually unchanged when driving 2 Lambda Pro's.  Also, for that matter, driving 2 SR-007's, the voltage swing will be about the same as with just one pair.  With SR-007's, that voltage swing is not quite enough, but one pair or two, there's almost no difference.

 

[svyr]

Stax headphones are not power hungry.  In fact, they use almost NO power.  They want VOLTAGE SWING, which is NOT the same as power.
 
You can plug in 2 Lambdas, it works OK.  Stax headphones don't really use any current.... just voltage. Two sets of Lambdas won't load it down, really.  (or 407's 0r 507's etc)
 
And 2 sets or SR-007's will work about as well as one set; which is to say, you get sound but really they need more voltage swing  than the usual Stax boxes can provide.
 
Voltage is not the same as power.  With dynamic headphones, they actually consume power - with Stax headphones, they want voltage but use hardly any current.  That's the same as saying they don't really consume much power.  So adding a second set does not significantly load the amplifier down.  Voltage swing with a single Lambda Pro from an SRM-T1  is virtually unchanged when driving 2 Lambda Pro's.  Also, for that matter, driving 2 SR-007's, the voltage swing will be about the same as with just one pair.  With SR-007's, that voltage swing is not quite enough, but one pair or two, there's almost no difference.

I think what people are having a problem telling apart is the 'voltage swing' from the max output voltage (L+- and R+-), from the rated PSU voltage (R-R or peak or RMS?), drawing a distinction between these would help...

 

[livewire]

Ok, I'm no EE but I will try to explain this voltage relationship in a fairly simple manner.
Using the KGSS design as a reference point, we will start with the power supply output which is
+350 volts DC and -350 volts DC referenced to 0 volts (ground).
So here we have a total direct current (DC) "voltage swing" potential of 700 volts.
 
These voltages, +350 and -350 are connected to the amplifier board.
We use the term "rails" to denote the individual "voltage highways"
that the positive and negative voltages travel on. Some use the term "buss" instead.
 
Inside of the amplifier board is where all of the voltage transformation magic occurs.
The DC voltages from the power supply are turned into "quasi AC voltages"
that conform to the audio signal that is applied to the amplifier input terminals.
 
The amplifier's job is to magnify the small (~2V) audio input signal, then output it to the headphones.
The KGSS employs four "gain stages" to do this along with a volume control that "attenuates"
or cuts back on the maximum possible gain to control the outputted level to something that is comfortable for listening.
For more reading on the KGSS theory of operation, please click on the following link and read "How it works":
 
http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=gilmore2_prj.htm
 
Getting back to the "quasi AC voltages" mentioned above,
The small two volt audio signal (from the source) is an alternating current (AC) voltage, also known as a varying sinusoidal waveform. (sine wave)
Inside the amplifier, this low voltage AC audio input is superimposed over the DC high voltage that has been fed in from the power supply,
thus magnifying the AC input signal and turning the DC rail voltages into a "quasi AC" output voltage in the process.
 
This is where the concept of RMS and peak to peak (p-p) voltages comes into play, expressing the maximum peak potential for these varying AC sine wave voltage swings.
If one wants to learn about RMS, wiki explains it well: http://en.wikipedia.org/wiki/Root_mean_square
Suffice it to say that RMS voltage is the part of the AC voltage waveform that actually does the work.
Roughly speaking it comprises the lower 2/3's of the AC waveform,
the "peak voltage" comprises the rest and is of relatively short duration when encountered during extreme amplitude excursions of the audio signal. 
Good thing, because if it did persist and packed a "current punch", it would burn out the electrostatic drivers on the headphones.
Stat amps are designed so the RMS rail voltages do not exceed the bias voltage (current Stax = 580VDC bias) 
so as to prevent excursions of the diaphram into the stators, as that could cause arcing and burnout.
 
+350VDC to -350VDC = 700V DC voltage swing at power supply (not to be confused with AC voltage "peak to peak" voltage.)
Therefore ~~~~~~~~~~~700V AC RMS voltage swing inside of the amplifier ~= 1KV AC p-p voltage swing. (full waveform, positive and negative going phases)
 
FWIW, Stax and most manufacturers reference the DC or AC RMS rail voltages for their products. Not the less meaningful, although greater peak to peak values.
 
I'm sure that someone will come along to correct me in at least few aspects of my diatribe.
Please note that the concepts above are approximations to get an idea or three across. I have not referenced applicable test frequencies, etc.
 
 
 

 

[deadlylover]

The voltage swing rating we are talking about takes into consideration the maximum and minimum voltages of the stators.
 
In case of the KGSS with it's +/-350V rails.
 
+350 front to -350 back gives +700V front to back
-350 front to +350 back gives -700V front to back
 
Which results in a maximum voltage swing of 1400V p-p. Note that a circuit can't actually swing all the way to it's rails, and a DC offset will lower this further, hence Headamp's rating of only 1200V p-p, which takes these losses into account, and perhaps leaving in some headroom.

 

[Electrostax]

This thread is approaching 1.000.000 views! ....    

 

[Duggeh]

Carl would be proud.

 

[edstrelow]

Quote:

Carl would be proud.

If you add the old Stax thread it is well beyond 1,000,000.
 

 

[wink]

Stax of viewers.................

931,523 of us wretches.....

 

[jcx]

you'd think if some people had gainful employment they could buy Stax systems for the time they've spent reading about them