[Sugano-san]

It is my understanding that the Stax 007t amp is basically a tube amp that has the additional ability to provide 580V of static voltage in to the diaphragms in the Omega II headphones (or 230V when taking into account the non-pro headphone output).

It is also my understanding that the amp itself (ignoring the static voltage for a moment) does nothing more than amplify the incoming signal, much like any other non-electrostatic amp. The amplified signal is fed to the two pairs of electrodes in front of and behind the charged diaphragms, which then vibrate in accordance with the amplified signal.

Assuming that the above description is correct (and if it isn't, please correct me), wouldn't it be possible to build an adaptor/cable or the like which connects the amplified output from an amp like the Stax 007t to a regular headphone but does not provide any conductor for the static 580V voltage.

That way one could drive a regular headphone with the output of a Stax (or similar) amp without ruining the headphones. If the amp is balanced, one would even take advantage of that feature as well with a regular headphone.

Is there a fundamental flaw in my assumptions?

Has the above ever been attempted? If yes, how does it sound?

Does any of the amp gurus care to reply? That would be most appreciated!

 

[kevin gilmore]

It is the required output voltage swing that prevents you from doing this.
Some of the amplifiers put out 500 volt peak to peak swings per side.
Other amplifiers like my blue hawaii put out 750 volts peak to peak per side.
These voltage swings are more than 100 times the voltage swings found
in dynamic amplifiers.

 

[Sugano-san]

Thanks for your reply, Kevin. On another note, would you happen to know if the Stax 007t is a phase-inverting amp or not?

Thanks.

 

[kevin gilmore]

It is not phase inverting from the unbalanced input. However from
the balanced input you can certainly flip hot and cold and get a
phase inversion. Or hook an unbalanced input to the cold side of the
balanced input and ground the hot side.

 

[Sugano-san]

Thanks again for your reply! I have one other and completely unrelated question, but since this is my thread, I can go OT as much as I want!

I found on headwize the following sentence, which may sound familiar to you: "My design ended up with a fairly large amplifier pulling significant amounts of power which results in a very smooth and extended frequency range from DC to over 200khz (-3dB at 400khz)." (emphasis added)

I read on head-fi your criticism of somone else's casual use of the expression "DC" in a comparable context. When I saw the statement above, I thought, it can't be such a grave mistake to say "DC", can it?!? Or am I missing something here?

Thanks.

 

[kevin gilmore]

My designs are fully dc coupled. They respond to dc signals as well
as ac signals. The phase shift of my amplifiers are absolutely 0 degress
at very low frequencys.

The other amplifier has an output capacitor between the output stage
and the headphones. No capacitor no matter how big can pass dc.

So when they say 0 to 50khz with less than 1db they are flat out
incorrect.

And when they say 0.01Hz to 0.1 Mhz within less then 0.5db
they are flat out incorrect again. With that capacitor and a 32 ohm load
the amplifier is actually 8db down at 10hz. And much more than that at
.01hz.

Why does it matter, because at low frequencys the output capacitor
causes significant phase shift. And electrolytic capacitors specifically
do all sorts of wierd things you would not expect at low frequencys.
Not the least of which is signifcant inductance.

 

[Sugano-san]

Thanks again, Kevin! This turns out to be a very educational thread!

One more question: Of the three different designs on headwize (tube, solid state, hybrid), which one is your [current] favorite? I think I remember you wrote that you prefer the solid state over the tube, but I am not sure if that was before or after the hybrid came out.

Thanks.

 

[kevin gilmore]

The blue hawaii is my current favorite electrostatic amp.
It is likely to stay that way for quite some time.

 

[Sugano-san]

Thanks again, Kevin.

I just looked again at the descriptions and photos of your amp designs on headwize. The Blue Hawaii's design is certainly very clean, and the result looks very impressive (especially with the separate PSU). I just can't imagine that this amp sound anything less than amazing (assuming its well executed).

Although I am not an expert, based on what you posted above, it also appears to circumvent the shortcomings of other, albeit more expensive designs. I would really like to compare it with a 007t, but even from just reading the description it seems that the Blue Hawaii is much more powerful and that fact would most likely be easily audible.