Ray Samuels Audio A-10 Thunderbolt II

General Information

There are 26 A-10 Thunderbolt IIs in existence right now (excluding 2 Ray uses as his personal systems). Mine was picked up earlier in December 2020 leaving only 2 possible A-10 left to be produced by Ray.

Below is a summary of the A-10 Thunderbolt II design from Ray Samuels himself in a Head-Fi thread:

The A-10, Electrostatic Amp/Pre-amp has a fully balanced input to output circuitry, with two balanced inputs, XLRs, and three SE, RCAs. The input/gain stage incorporates two 12AX7 tubes that handle balanced input signals via four section balanced DAC attenuator. In the Pre-amp mode, the signal is passed to two 6SN7 tubes, via relays, which are used as pre-amp output stage ONLY. If electrostatic phones have been selected, the input of the two 6SN7 is grounded to minimize noise and the signal is routed to four 5687 tubes, via relays, which are used as drivers for the phones. When a single ended signal is used, it is routed, via relays, to a single 12AX7, center tube. This tube is used as a phase splitter with a gain of two for both channels. Then the signal is routed to the balanced attenuator which passes it to the two 12AX7 in the gain stage. Because of this design the preamp XLR output will always be in balance even though the SE input source has been used. Also the SE outputs will be available at all time. The A-10 has a balanced and a SE tape loop. The selected source input will be present at these outputs without pre-amplifications to the signals.

The four 5687 tubes are configured in a SRPP topology, each tube drives one phase of the signal. When the Pre-amp is selected the inputs of all four 5687 tubes are shorted to ground to minimize noise. All resistors used are of the highest quality 1% 3 watts film resistors by Vishay. The A-10 also incorporates caps made by Hoovland, the Musicap are the best sounding polypropylene caps in the audiophile world, they are use where needed with a great result. The A-10 uses the mil specs boards that are meant to last a life time, these boards don’t come cheap, with these boards, a mil specs solder is used. All parts are hand selected, matched and soldered. There are no cut corners when it comes to the method of implementing the parts. We match them 100% value wise in all four sections of this amp.

All signal paths and power lanes are separated from each other. They are laid the proper way to ensure that the signal travels clean without any noise added to the output. Parts that are not used during the pre-amplification their inputs are shorted to ground the same is true when electrostatic phones are used, all pre-amplification inputs that are not used are shorted to ground thus the amp becomes a dedicated amp to the mode you select.

The A-10 is designed to work with HE90, HE60, SR007 and the Jade. It is capable of driving all these headphones with utmost authority and control to levels beyond what the human ear can handle without any hesitation, clipping or distortion. You can run two phones at the same time without any problem of loss in quality of sound reproduction.

There are four different voltages in the power supply of the A-10. The bias voltages are fully regulated, no changes as the AC line fluctuates. The A-10 power supply hosts many stages of rectifications & voltage regulation to ensure that the A-10 is always ready to deliver the right voltage & current when needed. There is no compromise when it comes to the heart of the power supply, as we implemented a custom built, to our specs, Toroidal transformer from Plitron.
All the resistors used in the power supply are of the highest quality with Mil specs and 1% tolerance. We also used the high temperature Panasonic electrolytic caps as filters.

Both chassis are made from solid aluminum. They cost a lot. Every part is made to our specs with ultimate accuracy and 100% precision.

Latest reviews

A-10 Thunderbolt II
Pros: Provides the SR-009 / SR-009S with a full musical spectrum
Includes full function preamplifier section for 2 channel systems.
Cons: Only supports electrostatic headphones
Expensive (requires NOS for best performance)
Only 2 left to be built
On March 29, 2009 Ray introduced the A-10 Thunderbolt II to Head-Fi. The 1st post of the earlier link describes Ray's design for the A-10 Thunderbolt II. Since then, Ray has continued to improve the A-10 as even the early A-10 had some of the same electrostatic restrictions as other similar electrostatic amplifiers. It had the speed and clarity but in my opinion they all still lack really natural sub-bass and bass and just left you wanting. As I looked back through that thread, I saw I was extremely excited about the A-10 but found myself hesitant about going down the electrostatic rabbit hole. For over 10 years I was able to keep myself out of electrostatic systems even while listening to them at meets and shows.

Fast forward to October 2019 and I found myself up at Ray's workshop having my Apache tested out. As I talked with Ray about what he has been doing since slowing down in the headphone amplifier world, he told me he made some changes to the A-10 and I should hear them. I really didn't want to since I had avoided this rabbit hole for over 10 years but ended up going upstairs to his home and listening to his personal A-10 Thunderbolt with his Stax SR-009. Ray mentioned he had focused on the pairing of the A-10 with the Stax SR-009 and with these latest improvements felt the SR-009 actually was exceeding the sonics of the HE-90s and as such he had sold those. I said "what, you sold your HE-90s? Those and your R10s are the best out there." As many know, Ray just smiles and hands me the SR-009 to have a listen. As they say the rest is history. I could not believe what I heard. My regular day to day listening had been with the Apache and the Focal Utopias. I honestly didn't think it was going to be close but I was wrong.

The SR-009 had the speed and clarity one comes to expect but the entire musical spectrum was now in the presentation. The sub-bass and bass were there in full. They weren't boomy but instead they were at the same level as the speed and clarity of the mid-range and treble. Everything just came together and really pushed this beyond any expectation I had. It really does not seem to matter what I listen to. I can put on a Qobuz playlist and I just sit back and enjoy the music, even if I am not familiar with it. Okay, well not all as there are a few genres I just can't find myself getting into.

I have also had the opportunity to compare the A-10 Thunderbolt II with the SR-009 to his B-52 using either his Sony R-10s or my Focal Utopias. There is no doubt his latest improvements took the SR-009 to a level I never expected.

I spent over a year trying to talk myself out of going down the electrostatic rabbit hole but obviously I failed. For those Star Trek fans, "Resistance is Futile" so I broke down and ordered the A-10 and purchased a pair Stax this year.

This isn't your typical review, just my story of how a headphone amplifier and pair of headphone impacted me and I wish others had the opportunity to experience. This truly is what Summit Fi is about. This listening experience just creates such an emotional connection to the music and brings out so much realism.

As I write this summary on New Year's Eve, I wish everyone a great new year and hope your search for musical connections can be fulfilled as mine has been with the A-10 and the Stax headphones.
Last edited:
Audio Addict
Audio Addict
In follow up to @John Massaria comment, my updated Apache to revision 4 shipped back today.:)

PS:. I did not think the S2590s would fit in the two outside DIP sockets??
Audio Addict
Audio Addict
Just a quick update. Even with Revision #4 to the Apache paired with my Utopias and the DirectStream DAC, this setup still falls short of the A-10 Thunderbolt II / Stax setup.
iFi audio
iFi audio

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