[SmellyGas]

Quote:

Originally Posted by 00940 /img/forum/go_quote.gif I dunno... maybe because it's a top of the line Stax design I simulated ? Maybe because many of those available stat amplifiers are still tubes based ? Maybe because there's a reason designers continue designing tubes based amplifiers (hint: high voltage and transistors don't mix well) ?

And many Stax designs are solid-state. The Stereophile reviewer of the original SR-007 preferred the solid-state over the tube amp. Kevin Gilmore has a well-regarded KGSS amp. (hint: "SS" stands for solid-state). So I'm not sure where you get off saying "high voltage and transistors don't mix well" because it's obviously wrong.

Quote:

I thought you were approaching this as a scientist... define "sound better". However, I would indeed suggest that most electrostat headphones amps have an unique distortion pattern (level and harmonic distribution) which can reach audibility levels. How else would I justify that different amps sound different ?

Well, first, you still have yet to establish that the levels of distortion in SOLID STATE amps are even close to the level of audibility, making a "unique distortion pattern (level and harmonic distribution)" otherwise irrelevant. According to Stax specs, THD is < 0.01% on their 727 solid-state amp at a reasonable output, which makes THD an unlikely cause of differences between SS amps. THD is certainly not apprecialy different among SS loudspeaker amps driven below clipping.

Quote:

You are over simplifying the argument. "Lots of power" must be judged wrt the available amplifiers. And obviously, some of those lack the power necessary to reach properly high sound level at high frequencies and thus probably distort already at lower levels.

I find it hard to believe that any commercially available electrostat amp (except for maybe a battery powered one, maybe) does not have the power to drive a typical Stax headphone at normal listening levels. Really, now.

Quote:

Oh really ? Please remove that "certainly cannot". I assure you it isn't so easy to design a solid state amplifier, with a correct frequency response, which can run on +/- 300V supplies and swing that much voltage/current properly. Ask the guys who just designed a diy stat amplifier. Sorry but you are making wild assumptions here.

Okay. It's not easy to design a loudspeaker amplifier that puts out 100W either, but engineers have seemed to figure that out too.

 

[00940]

It's quite easy to design a 100W solid state amplifier for loudspeakers as the transistors needed are commonly available and you can follow the usual, well documented topologies (those giving those lovely consistent results on the test bench).

On the other hand, high voltage transistors suitable for audio design are a rarity (some of those used in the KGSS are getting difficult to source or replace). Then comes the challenge of stabilizing amplifiers with huge gain (500 for stax, 1000 for KGSS), to which you must add more open loop gain for feedback. Kevin Gilmore chose to go with very little feedback (6db), stax with higher feedback.

End of the off topic on transistors and high voltage.


I just noticed that, beside the battery powered one, all stax amps are now quite power hungry (29W to 46W for SS ones, tubes are higher but the heaters factor in). The 10W srm310 is discontinued. 30W of total consumption seems right for managing 100db at highish frequencies with current Stax headphones (those amps are single ended class A, they cannot provide more current than at idle).

So, to summarize stuff:

- to reach realistic peaks of 100db at all frequencies (it doesn't seem overly crazy for a requirement), the current AC powered amps by Stax seem allright (starting with the srm323II). The 4W battery amps... I wouldn't count on it.
- it is quite probable that tube amps without (much) feedback have varying THD up to the level of audibility, depending on the design choices.
- I'm curious about the KGSS with his 6db of feedback, how does the THD wander with power/frequency. (simulations are difficult because of the lack of adequate transistors models...) On the other hand, it has lower output impedance than the stax amplifier for which I've the schematics (srm323).

 

[SmellyGas]

Quote:

Originally Posted by 00940 /img/forum/go_quote.gif End of the off topic on transistors and high voltage.

LOL okay. I don't disagree with what you wrote.

Quote:

I just noticed that, beside the battery powered one, all stax amps are now quite power hungry (29W to 46W for SS ones, tubes are higher but the heaters factor in). The 10W srm310 is discontinued. 30W of total consumption seems right for managing 100db at highish frequencies with current Stax headphones (those amps are single ended class A, they cannot provide more current than at idle).

People here are seem very certain that there are EASILY-AUDIBLE differences among various Stax amps, including the 310, 312, 717, 727, 006, 007, and KG's offerings. Their explanation has invariably been that differences in "sound quality" are due to differences in POWER. Do you think this explanation has any merit?

Quote:

- it is quite probable that tube amps without (much) feedback have varying THD up to the level of audibility, depending on the design choices.

This may be true, but tube amps for dynamic headphones and tube amps for loudspeakers have increasing THD with output as well.

Quote:

- I'm curious about the KGSS with his 6db of feedback, how does the THD wander with power/frequency. (simulations are difficult because of the lack of adequate transistors models...) On the other hand, it has lower output impedance than the stax amplifier for which I've the schematics (srm323).

The impedance of 160pf Stax electrostatic headphones can be estimated by the capacitative reactance, and is anywhere from 50kohms to 50Mohms = extremely high. Do you think that the differences in output impedance among the various electrostat amps really make a difference when driving such a load?