Stax Driver Comparison

Has anyone compared SNR of the Stax SRM-006tII and SRM-007tII to older Stax tube drivers such as the Stax SRM-006t? I want to evaluate 24 bit digital systems using Stax earspeakers and so starting with the quietest Stax drivers will be a good start.

I have an older solid state Stax driver and am interested in upgrading to either the SRM-006tII or (if there is a huge difference in sound) the SRM-007tII. I haven't heard either one. I have SR Lambda Pro earspeakers and wouldn't mind getting a newer earspeaker model either, but first I'd like to know that I have a new quiet driver.

Stax says the new tube drivers use DC heater supplies rather than the older AC heater supplies, reducing power supply hum and thereby improving SNR. They made further other changes (such as extending frequency response) to better match the capabilities of SACD and 24 bit DVD Audio. Yet I haven't found any information on their website or in a review about what the SNR was in older units, and what it is in newer units, or at least how much of an improvement in SNR there actually is in their newer drivers.

Part of the reason might be that they hand-pick front-end FETs for low noise, so what they select could vary from one batch to another and they can't commit to an absolute SNR limit. That's just conjecture though.

By being better able to match the capabilities of SACD (effectively 20 bits per sample) and 24 bit DVD Audio, does that mean their older drivers did not have, say, approximately 120 dB SNR to at least match 20 bit digital samples but that their newer drivers do? Is the SRM-007tII significantly quieter than the SRM-006tII?

Does Stax have a solid state driver that is quieter than the SRM-007tII?

Thanks for any comments.
Not sure of 120dB SNR, seems to be unrealistic in any ways especially in tube equipment, but going from AC to DC heater supplies does improve SNR.
As to comparing SNR vs. solid state driver, SS wins. What you gain with tubes is holography, speed and slam.
Thanks. I guess I'll look at the SRM-717 or SRM-727 expecting them to have a lower noise floor than the tube drivers. It would be nice if Stax could spec some sort of EIN.

I know and love the tube sound well. My preamps and amps are all tube-based. I prefer tube sound but in this case I want the lowest noise floor possible to evaluate the noise floor of other equipment. If I knew that the noise floor were low enough, I could consider getting the SRM-006tII or SRM-007tII and leaving it at minimum gain.
You might be better off with one of these. They are reviewed much higher than either of the Stax amps.
Besides the SS and tube offerings from the site above, if you go with tubes you can also check out the WES from
KGSS is not on sale : it's a DYI
Judging by the dates of this thread, it may be too little too late but I feel compelled to make a comment. I owned the same solid state Stax combo as the poster of this thread, for about twenty years and was very satisfied until I finally bought an SRM-T1 tube driver unit with Lambda Signature phones here on Audiogon. It was a huge difference, owing to the tube driver unit, I believe. I keep thinking I'll buy some 007 or 009 phones but, at more than twice what I paid for this combo, I always hesitate to pull the trigger. I will buy one soon. But, back to your issue, you might look at some of these new orthodynamic units from HiFiMan or Audeze, they look promising and sound great!
Via a posting on headfi about a STAX factory visit, STAX still uses the SRM-T1 as a reference in developing their current top of the line headphones.

The problem with the SRM-T1 is finding super low noise NOS tubes from the 60's and 70's for best results.

Try Tube World, they sometimes have the RCA clear top NOS tubes that are best.

You also need to re-bias the driver. See Headfi for info.