This article is an attempt at writing a small guide for getting into the world of Stax electrostatic headphones. I personally just bought my first Stax system and I´ve never been this impressed by any gear so far during my headphone hobby. The world of Stax headphones can look a bit scary: confusing codenames for products, not many reviews out there and limited availability. I was completely confused when I first got interested in electrostatic headphones and did a lot of reading all over the internet. Personally I feel Stax gear is not really getting the amount of exposure they deserve, even though they have a very dedicated (and often vocal) group of fans. So yes, I´m trying to spread the good word :) And no, I have zero financial connections to the company.
First, some brief history about me. I started with a NuForce Icon HDP, but then quickly caught the upgrade bug (rumour has it it´s pretty common here). After that I went through two amps: Audio-gd Phoenix and Violectric V200. I´ve also auditioned the Lehmann Black Cube Linear, Benchmark DAC-1 and the Cambridge Audio DacMagic. The headphones I went through: Sennheiser HD 800, Audeze LCD-2, Sennheiser HD 650. While I loved many features these dynamic and orthodynamic (LCD-2) headphones had, none of them were good enough. There was always a critical flaw, something that annoyed me too much. In the HD 800 it was the treble-heavy sibilant fatiguing sound, in the LCD-2 it was the small congested soundstage and lack of high frequencies. Out of these, the HD 650 was my favourite as it had nothing that annoyed me too much, but it did not match the other headphones I tried in certain other features. So long story short: I still wanted more. I wanted a lot, but at the prices these high end headphones are sold at, everything in the end was a disappointment. Some more than others, of course. My main disappointment was the Audeze LCD-2. Anyway, out of all the purchases I made, almost everything ended up sold on various hifi forums as the quest for something close enough to perfection continued. The only thing that I was completely happy with was my first DAC purchase after the Icon HDP, the Audio-gd Reference 7. It´s still my source and I feel no urge to switch.
After trying the leading dynamic and orthodynamic headphones, I slowly become interested in Stax. They were a pretty big question mark for me. It was much harder to find information on them. Then I had the chance to audition a used Stax system (SRM-006 and SR-404 Limited, I´ll explain those later). Even though it was far from the most expensive Stax system out there, it left me really impressed. It managed something nothing else so far could do: a neutral sound that is highly detailed, yet still musical. And no treble roll-off was needed to make it easy to listen. It was just, as Steve Jobs would say, magical!
The basics:
Stax calls their amplifiers energizers, and their headphones earspeakers. Their earspeakers only work with special purpose (for electrostatic) amplifiers. So if you are coming from the dynamic/orthodynamic world, you will basically have to buy a new amplifier as well. Stax are not your standard dynamic headphones (see to see the operating principle in most headphones on the market). Stax is the one of the very few companies that still make electrostatic headphones. Sennheiser used to make them too, but for unknown reasons they are no longer being sold. Most likely they weren´t profitable enough. So what is this this "electrostatic" mean? See and The word energizer is most likely (this is my speculation) used because of the high voltages their amplifiers output. While there isn´t that much power in a HD 800 cord during playback, it´s a very different with electrostatic headphones. Some have raised safety questions, but Stax has been around for decades and have a good reputation. Just follow their security tips in the manuals.
There are two lines of products in the Stax world: (1) Lambda and (2) the high end research line. The Lambdas are the mainstream model, while the second option currently only includes one headphone: the SR-007MK2. In the near future, another product in this range is anticipated (rumored to cost even double of the SR-007MK2). 
This guide will only talk about the Lambda world. Why? Because they are not extremely expensive and are less picky when it comes to amplifiers. The more experienced Stax fans generally seem to think (not just here, on various forums) that the current amps Stax makes are not good enough to drive the high end research line products. They are ok for Lambdas though.
While Stax have a reputation for being expensive, part of this is because many associate them with their flagship high end lineup. The Lambda products are not any more expensive than a standard dynamic or orthodynamic setup (for example HD 800 + amplifier, HD 650 + amplifier etc). They represent, in my experience, excellent value for money. Stax products also have a reputation for being very durable ("from father to son"). There are many vintage Lambda models in the used market these days, and many sets that are from the 80´s etc still perform well. Last but not least, the resale value in Stax products in generally quite high as they have a very dedicated fan base.
The current Lambda lineup (earspeakers):
All current Stax Lambda headphones require amplifiers with pro-bias output sockets. These are available in all currently produced models. Some older Stax amps in the used market might not have them though. If you are buying relatively recent gear, then you won´t have to worry about this.
Right now Stax manufactures these Lambda models...
(1) SR-507

Price: around 1050-1100 dollars in the US, around 900 dollars imported from Japan via a site like In the EU, pretty much the US price in euros.
This is their current Lambda lineup flagship, released september 2010. Compared to other in production Lambda models, it has an improved headband, leather pads and an improved cord. Most importantly, it´s got a brand new driver. Why is this such a big issue? Lambdas have been around for decades, and this is the first major upgrade in a very, very long time. Thus it´s a very good time to be be on the market for these. 
In a way this Lambda is the return of the older SR-404 Limited model, of which only 1000 were made (it used the same premium pads and cord for example). Now it´s no longer necessary to hunt the used forums. The SR-404 Limited was considered the best Lambda so far, and the early reports on the SR-507 around the web seems to indicate the new flagship is on the same level.
(2) SR-407

Price: around 600 dollars imported from Japan via a site like US and EU prices unknown, as most dealers don´t seem to have these yet.
This is, judging by what I´ve read around the web, the best value in the range, as it supposedly performs very close to the SR-507. So it´s cheaper than a HD 800 or T1 :)
(3) SR-307
Price: around 500 dollars imported from Japan via a site like US and EU prices unknown, as most dealers don´t seem to have these yet. Also fantastic value for money, but I have no idea how much this differs from the 407.
(4) SR-207
There´s also the SR-207, which is even cheaper. It´s only sold together with the SRM-252S energizer as a package. The combo costs 700 dollars imported from Japan. Local prices vary, so ask your dealer. As usual, generally it´s around 10-15% more expensive in the US, while EU people have to pay pretty much the same in euros.

The current amplifier lineup (energizers):
First you´ll need to decide if you want tubes or solid state. Stax offers both. The official line from the Stax site is that the tube ones offer less listening fatigue. Is it true? No idea. In general that is what tubes are traditionally good at though. Stax offers two combo packages: SR-407+SRM-006 and SR-307+SRM-323. The first one is a tube amplifier, the second is a solid state. In trade shows Stax has recently been demoing the SR-507 with the SRM-600 tube amp.
While it doesn´t really matter if you import the earspeakers (they don´t care what voltage your Stax amp runs on), the issue of voltage zones has to be raised here. If you order directly from Japan, you´ll need to use a voltage converter which can be a pain (some claim it also affects the sound, I doubt that). As with all Stax products, the japanese warranty is only valid inside Japan. So if you get any problems, you´ll need to ship your gear to the website staff so they can get it repaired. The easiest way, of course, is to buy everything through a local distributor. Then you won´t have to worry about voltage zones. But you can also buy the amp from a local distributor, and then the headphones through an importer.
Tubes look nice, so I´ll talk about them first. You have two main choices for Lambda (assuming you want to use the official currently in production Stax amps):
*disclaimer: I´m ignoring the Stax SRM-007tII tube amplifier here as it´s listed in the "high end range" products on the official Stax site. It´s also very expensive, and at that cost there are many third party alternatives as well (and they are from what I´ve read more suited for running the Stax research high end line)
(1) SRM-600

Price: around 1400 dollars imported from Japan. Price elsewhere unknown.
This is a limited edition (600 made) version of the SRM-006 that uses different tubes. The tubes it uses are the JJ Electronic ECC99. There are two dual triode tubes, one for each channel. It has an output max power of 340V (which is as high as the flagship SRM-007 tube amp that I´m not covering here). This amp was originally made as a 35-year anniversary product to complement the SR-404 Limited. As the SR-507 is rather similar to that, it seems to be a very good pairing judging by what I´ve read (and I have that combo at home, love it!). What pushed me to buy one of these is that I found a few pictures on the web that showed Stax demonstrating the SR-507 with this. If it´s good enough for them, it´s good enough for me. Accepts balanced input (XLR) in addition to single ended RCA.
Right now these are still on the market, but won´t be for long. If you want one, you might need to hurry.
(2) SRM-006tS

Price: around 1200 dollars imported from Japan. Ask your local dealer for their price.
This is a true classic. It´s based on an older design that has been around for a long time. It´s a safe choice, and the one Stax bundles with the SR-407. Runs two dual triode 6FQ7/6CG7 tubes. Accepts balanced input (XLR) in addition to single ended RCA. Output power is 300V.
The SR-407 + SRM-006tS combo costs around 1700 dollars imported from Japan. Local prices vary. In general US prices are around 10-15% higher than in Japan. In the EU it´s a different story (read: much more expensive).
If you decide to go solid state instead, Stax have a nice little gem waiting for you as well!
*disclaimer: I´m not covering the high end SRM-724 solid state amplifier here as it´s listed on the Stax site as belonging to the high end range. It´s also a controversial amp, as many feel it has a flawed implementation of NFB (it´s the first Stax amp that doesn´t use negative feedback). Many experienced Stax hobbyists say it sounds good after a small mod though. Anyway, it´s not a very common choice for a Lambda so I´ll skip it.
(1) SRM-323S

Price: around 800 dollars imported from Japan. Local prices vary. Once again, ask your dealer :)
This is, according to many very experienced Stax enthusiasts, a real steal at the price. Actually Spritzer on these forums considers it the best amp Stax currently makes. So value is very high here. Output power is 400V. Does not have XLR inputs (single ended RCA only).
Together with a SR-307 the bundle price is around 1200 dollars imported from Japan. The bundles are also on sale via distrobutors.
The official Stax distributor contact information for different countries can be found here:
Some final words:
So all in all, Stax Lambda rigs don´t have to be that expensive. Sure they are not very cheap, but if you are considering 1000 dollar amplifiers for dynamic headphones, we are talking about the same price range already. The Stax gear offers a very unique sound that is very different compared to more common dynamic and these days orthodynamic headphones. The downside is obviously that you are locked into electrostatics as the amp can only run them. However, many like the Stax sound so much they wouldn´t consider anything else anymore anyway. Personally I´m one of those. I can see myself upgrading to a high end Stax research line product and amplifier someday, but not in the near future. For now, this is the first setup that I´m completely satisfied with. I by far prefer the SR-507 over the Sennheiser HD 800 or the Audeze LCD-2 (oh and I have to say I also prefered the old SR-404 Signature to those as well). As someone who used to swap gear around a lot, that says more than a long list of sound signature adjectives. Also with Stax, you don´t have to worry about the very often underestimated problem of system matching. Anyone who has tried the Sennheiser HD 800 will know that they are a pain to get right. Electrostatics, in my opinion, are a "buy and enjoy" solution. These days I´m only interested in portable gear, speaker gear and future DAC products.
My Stax Lambda system offers the best microdetail, clarity and instrument separation I´ve ever heard out of a headphone system. All this while not being fatiguing or sounding dull and analytical. But of course the Stax sound is not for everyone (as all things in hifi, electrostats also divide opinion), and I´m not trying to say it is. If you want to know if the Stax sound is for you, my recommendation would be to go to a meet and listen to some Lambda gear. You´ll quickly notice if you also fall in love with the effortless, delicate delivery that Stax gear excells at. 
PS: I´m NOT trying to claim I´m an expert when it comes to Stax. The point of this post is to help others out there who might be considering Stax Lambda gear, but find the whole electrostatic world too confusing. Any feedback, changes and recommendations from more experienced HeadFi´ers is very much appreciated!
PPS: I intentionally posted this in the headphone forum, not the high end one as a Lambda rig is not any more expensive than a HD650 with a good amplifier. If the mods feel this should still rather be in another forum, feel free to move it :)
Edit 1: fixed some typos... I´ll fix more later.
Edit 2: fixed some more stuff and added pictures.