Listening to the Stax SR-009 and Great Headphone Amplifiers Ray Samuels A-10 Thunderbolt
Ray Samuels Audio A-10 Thunderbolt ($6500)
Bristling with features, the Thunderbolt is both an electrostatic headphone amp and a pre-amp. This amp is an all-tube design for the audio section with a separate solid-state power supply, and uses matched pairs of 5687 tubes for the headphones, with matched 6SN7s used for the analog outputs of the pre-amp. Two balanced inputs, three unbalanced inputs, and a tape and pre-amp output (both with balanced and unbalanced connections) grace the rear of the main electronics unit, which can rest atop or aside the separate power supply.
At normal listening levels, the A-10 seems the punchiest and most dynamic sounding of the amps. Bass notes are fairly tight and well integrated with the mids. The presence area of the upper-mids seem slightly emphasized relative to the rest of the midrange giving the vocals an up-front feel. The treble is articulate and well proportioned, but there seemed a slight "Ssss" emphasis in the mid-treble. The overall feeling I got from the A-10 was fun, sparkly, and a bit hyped up. It's not the type of sound I generally prefer, but it did seem to do it quite well and should satisfy listeners with that taste...at normal listening levels.
Like so many of these amps, cranking up the Thunderbolt brought out some of the above characteristics in a less pleasant light. To be fair, it did far better than the Stax amps, and somewhat better than the Woo with loud listening levels, but in the end the sparkle and hype got to be overbearing and gritty on most music, and downright painful on crunchy guitar tracks.
If you like your tunes a bit on the exciting side, this might be the e-stat amp for you. I'd be cautious of hard driving rock and metal, where the Thunderbolt may get too agressive, but with acoustic jazz and classical it will bring some added zazz some might like.
I'd say the more difficult question to resolve is whether you want to build your entire big rig around the A-10's pre-amp function. (Sorry, I didn't have time to check it out as a pre-amp.) It's certainly got the right look for it, but with all the tubes on all the time I would worry a bit about using up tubes when they're not actually being listened to.