Long-term perspective: My first encounter with STAX happened in the late 1980s. I bought my first system in 2003 and have since owned several Lambda models, tube and solid-state amplifiers, a DIY KGSSHV, an Omega 2 MK1 and, finally, the SR-009S. This article tells the complete story of that journey.

My STAX Journey at a Glance

I have owned enough STAX headphones and amplifiers that the sequence can become confusing, even to me. Here is the condensed version before I go into the individual systems.

My First Encounter With STAX in the Late 1980s

My relationship with STAX started long before I could afford one. In the late 1980s, I had the opportunity to hear a Lambda Pro connected to a tube-based amplifier. I was still young, and the complete system was far beyond what I could realistically buy.

The Lambda did not impress me with one spectacular bass note or an exaggerated treble effect. What stayed with me was how little it sounded like a mechanical device strapped to my head. It was open, fast and free from the slight boxiness or heaviness I associated with conventional headphones. Small details were present, but they did not seem artificially pushed forward.

I had already heard electrostatic loudspeakers from companies such as Quad and Martin Logan, so I knew how transparent and immediate a large electrostatic panel could sound. Hearing some of those qualities from a headphone was still a revelation.

I left without buying anything, but I never completely forgot the experience.

My First STAX System: SR-404 and SRM-313

I finally entered the STAX world in 2003 with a used SR-404 and SRM-313 solid-state amplifier.

The SR-404 was part of the Lambda family, with the large rectangular earcups and thin electrostatic diaphragm that define the classic STAX appearance. It was not the exotic flagship of the range, but it delivered the qualities I remembered from the Lambda Pro.

Compared with the conventional headphones I knew, the SR-404 sounded exceptionally quick and clear. Acoustic instruments started and stopped without obvious overhang, while voices had a directness that made many dynamic headphones seem slightly veiled.

The compact SRM-313 was a practical partner and easy to live with. More importantly, it allowed me to enjoy the SR-404 without immediately turning the purchase into a major electronics project.

That peaceful period did not last very long. Once I knew what the basic system could do, I started wondering how the SR-404 would perform with a more ambitious amplifier.

Building My First High-Amp Tube Amplifier

My first serious STAX amplifier project was based on a design by Andreas Rauenbühler of High-Amp. I built the unit myself and fitted it with Raytheon 6S4A NOS output tubes.

This was a separate amplifier from the SRM-T1 I owned later. The modified T1 used ECC99 tubes; the Raytheon 6S4As belonged to the home-built High-Amp design from my first STAX period.

The project appealed to me because I had been interested in electronics from an early age, and a dedicated electrostatic amplifier was a far more engaging challenge than buying another conventional headphone amp. The high internal voltages demanded careful component selection, layout, grounding and safe construction.

Once finished, the amplifier made the SR-404 feel more effortless and controlled than it had with the smaller SRM-313. The basic Lambda character remained intact, but the system sounded less constrained during demanding passages.

I kept the setup for several years before selling it around 2008. At the time, I thought I was simply moving on to other parts of the hobby. As it turned out, I had only taken a break from STAX.

Returning to STAX: Lambda Pro, SR-507 and Modified Amplifiers

My first attempt to return involved another Lambda Pro. Unfortunately, the example I bought was heavily worn. Vintage STAX headphones can remain functional for decades, but pads, headbands, cables, dust protection and driver condition all matter. This particular Lambda Pro was not the right basis for a long-term system, so I sold it again.

The proper return came with an SR-507 imported from Japan. At the time, it was the flagship of the modern Lambda range, retaining the familiar rectangular construction but adding more substantial materials and a noticeably more polished finish.

Its sound was fresh, clear and highly analytical. The SR-507 made leading edges, recording details and upper-frequency information exceptionally easy to hear. When I wrote the original version of this article, it was the best headphone I had personally owned.

The same character could become relentless with bright recordings or an unsympathetic source. The SR-507 was never a soft or forgiving headphone designed to make every album sound pleasant. Listeners who enjoy a crisp and explicit presentation may still prefer that approach to the darker balance of the Omega 2.

My first amplifier during this period was a used SRM-1/MK2 modified by Inexxon Audio, run by Sören Schulze. Although the SRM-1/MK2 was already an old design, the serviced and modified example drove the Lambda very convincingly.

Later, I used an SRM-T1 that had been completely recapped and fitted with ECC99 tubes. Its hybrid circuit combined a solid-state input stage with tube outputs. The rebuilt amplifier gave me another way to balance the SR-507’s direct and sometimes unforgiving presentation.

When I first published the article in 2015, the SR-507 and modified SRM-T1 were at the center of the story. I wrote that electrostatic headphones gave me exceptional clarity, low distortion and a particularly natural presentation with jazz, classical music and vocals. Every later upgrade changed the degree and tonal balance, but not that basic impression.

Trying the STAX SR-003 In-Ears

At one point, I also tried the STAX SR-003, one of the strangest products in the company’s catalogue: a genuine electrostatic in-ear earspeaker.

I was curious whether it could provide a smaller and more portable version of the STAX experience. It did offer some of the speed and openness associated with the larger models, but the fit and presentation were very different from a Lambda or Omega-series headphone.

The SR-003 also requires a compatible electrostatic amplifier. It is therefore portable only in relative terms and does not offer the simplicity of connecting a normal pair of in-ear monitors directly to a phone or compact headphone amp.

It remained an interesting side branch rather than a replacement for my full-size system, but I am glad I had the chance to experience it.

Building the KGSSHV

The next major step was a KGSSHV — the Kevin Gilmore Solid State High Voltage amplifier. Rather than buying a finished commercial unit, I decided to build one myself.

This was a considerably larger and more demanding project than modifying an older STAX amplifier. The KGSSHV operates with substantial internal voltages, produces heat and requires careful component matching, wiring and testing.

Once completed, it put an end to my questions about whether the system needed more amplifier power. The KGSSHV drove the SR-507 with excellent clarity and became even more important when I later moved to the less sensitive Omega 2. It eventually powered the SR-009S as well and never gave me a serious reason to search for a more prestigious brand name.

The amplifier remained in my system for years, but eventually developed problems after exposure to humidity. Troubleshooting a densely constructed high-voltage amplifier is very different from taking a normal consumer product to a local repair shop.

That experience did not make me regret building the KGSSHV. It did change how I looked at my next amplifier purchase. I had reached the point where long-term support and repairability mattered as much as the satisfaction of building something myself.

Moving to the Omega 2 MK1

In 2016, I sold the SR-507 and bought a pre-owned Omega 2 MK1, also known as the original SR-007. The move changed the tonal balance of my system far more than another small amplifier swap would have.

The Omega 2 sounded darker, rounder and more physical than the SR-507. Its upper frequencies were less forward, while the bass and lower midrange carried more weight. Instead of displaying detail in a crisp and obvious way, the SR-007 integrated information into a denser and more relaxed presentation.

I understood immediately why some listeners remain loyal to the original Omega 2 even after hearing newer flagships. It retained the speed, low distortion and transparent midrange of an electrostatic design without sounding thin or stereotypically bright.

The SR-007 was also more demanding to drive. It was less sensitive and less immediately lively than a Lambda, which made the KGSSHV a particularly sensible partner.

I kept the Omega 2 MK1 for almost eight years and eventually sold it without losing money. That is unusual for consumer electronics, but desirable older STAX models can hold their value remarkably well when they remain in good condition.

It was one of the most satisfying headphones I have owned. Replacing it required something genuinely exceptional.

The SR-009S Becomes My Reference

The SR-009S eventually replaced the Omega 2 and moved the system in a different direction again. It sounded more neutral, more open and more resolving than the SR-007 MK1.

This was not simply a matter of adding brighter treble. The SR-009S revealed more of the space around instruments, the texture of voices and the quiet information that gives a recording depth.

A well-recorded singer can sound unusually real. Consonants, breath and small changes in tone are clearly audible without automatically becoming sharp or artificially highlighted. The Omega 2 had more warmth and density; the SR-009S gives me a clearer view into the recording.

Its soundstage is also wider than that of my earlier Lambda systems and has more convincing depth. Headphones cannot create exactly the same external image as properly positioned loudspeakers, but the SR-009S is very good at separating the layers within a recording.

Poor or aggressively mastered albums remain poor and aggressive. The SR-009S does not disguise problems, but its low apparent distortion means it rarely adds another layer of hardness itself.

It is most convincing with acoustic jazz, classical recordings and natural vocals. Cymbals retain their speed without turning into a sheet of white noise, piano notes preserve both attack and decay, and subtle changes in a horn player’s breath are easy to follow.

The headphone also performs particularly well at moderate volume. I do not need to play loudly to recover detail or dynamics, which makes long listening sessions easier.

My Long Search for the Right STAX Amplifier

A STAX headphone is only half of the system. Unlike a conventional dynamic or planar model, it cannot be connected to a normal headphone output. It needs either a dedicated high-voltage amplifier or a transformer interface connected to a speaker amplifier.

Over the years, I have used almost every major approach:

• The compact solid-state SRM-313
• A DIY High-Amp tube amplifier with Raytheon 6S4A NOS tubes
• A modified SRM-1/MK2
• A recapped SRM-T1 with ECC99 tubes
• My DIY KGSSHV
• A used SRM-D50 that required a warranty repair
• A temporary SRM-400S
• A heavily modified SRD-7 transformer interface
• My current High-Amp Antares

The SRM-D50

The first commercial STAX amplifier I bought after the KGSSHV failed was a used SRM-D50. I deliberately chose an example that still came with a warranty, which turned out to be important.

The unit developed a fault during my ownership. Because it was still covered, I was able to have it repaired under warranty instead of taking responsibility for another uncertain high-voltage repair myself.

Once the repair had been completed, I sold the SRM-D50.

The experience reinforced something I had already begun to learn from the KGSSHV: with electrostatic amplifiers, serviceability and warranty coverage can matter just as much as specifications or sound quality. Buying used can offer excellent value, but only when a defect does not turn the saving into an open-ended repair project.

The SRM-400S

After selling the repaired SRM-D50, I bought an SRM-400S second-hand. It drove the SR-009S without obvious technical problems, but I missed the openness and authority I had become accustomed to from the KGSSHV.

Because I had also bought the SRM-400S used, I was able to sell it again without a major financial loss. It was a useful temporary solution rather than an amplifier I wanted to keep permanently.

The Modified SRD-7

One alternative I kept is a heavily modified SRD-7 transformer interface. An SRD box connects to the speaker outputs of a conventional power amplifier and transforms that signal to the voltage required by the STAX earspeaker.

Used with my DIY Hypex NCore power amplifiers, the modified SRD-7 sounds surprisingly good. It proves that a capable speaker amplifier and a well-prepared transformer interface can remain competitive with dedicated electrostatic amplifiers.

The High-Amp Antares

My current amplifier is the High-Amp Antares, built by Andreas Rauenbühler. The design is also available to experienced DIY builders, but this time I chose a completed unit.

After constructing several high-voltage amplifiers, sourcing components and spending many hours troubleshooting, I no longer felt the need to turn every system change into another construction project.

The Antares has ample power, remains cool in operation and lets the SR-009S sound open and controlled. It gives me the performance I wanted without leaving me responsible for maintaining another one-off build.

My current digital sources include the Eversolo DMP-A8 and the SMSL PL200. The Eversolo can act as the digital source, while the PL200 works very well as the DAC feeding the Antares through its balanced outputs.

The SR-009S is revealing enough to expose real differences between components, but those differences are usually smaller than changing the headphone itself. I discuss that issue in more detail in my DAC Buyer’s Guide and my article on cheap versus expensive DACs.

How Electrostatic Headphones Work

A conventional dynamic headphone uses a voice coil attached to a diaphragm and moves it within a magnetic field. An electrostatic driver works differently.

A very thin charged diaphragm is suspended between two perforated fixed electrodes, usually called stators. The music signal reaches the stators as a high-voltage push-pull signal. As the electrical field changes, the diaphragm is attracted toward one stator and repelled from the other, displacing air and producing sound.

Because the diaphragm does not carry a conventional voice coil, it has extremely little moving mass. It can start and stop quickly, contributing to the clean transient response and low apparent distortion associated with electrostatic headphones.

STAX was founded in 1938 and introduced its first electrostatic headphone, the SR-1, in 1960. The company traditionally refers to its headphones as “earspeakers.”

Modern Pro-bias STAX models require a constant bias voltage and a high-voltage audio signal that an ordinary headphone socket cannot supply. The amplifier or transformer interface is therefore part of the complete system, not an optional accessory.

What STAX Still Does Better for Me

Voices and Acoustic Instruments

Voices remain the clearest example of what keeps me interested in STAX. The SR-009S reproduces breath, phrasing, changes between chest and head voice and the acoustic space around a singer without making every consonant sound etched.

Piano, strings, horns and percussion benefit from the same speed. With a cymbal, I hear the initial strike, the metal vibrating and the sound fading into the room rather than a generic burst of treble energy.

Fine Detail and Spatial Separation

Fine details remain easy to hear even at moderate volume: fingers moving on strings, the mechanical sounds of a piano and the ambience of the recording venue.

Some highly detailed headphones create a sense of resolution by emphasizing particular frequency regions. The better STAX models present detail because the system is clean and fast, not because every musical edge has been sharpened.

Listening at Moderate Volume

Because information remains clear at lower levels, I am less tempted to increase the volume simply to make a recording feel alive. That makes long sessions more comfortable and is one reason STAX remains well suited to late-night listening.

Why Headphones Became So Important to Me

When I wrote the first version of this article, most of my serious listening happened through headphones. My children were younger, much of my listening took place after they had gone to sleep, and I did not have a dedicated acoustically treated room.

The living room was the center of family life. Large acoustic panels and a visually dominant loudspeaker installation were not realistic priorities. Headphones removed room reflections, reduced problems with neighbors and gave me consistent sound regardless of where the system was placed.

They also introduced compromises. A headphone does not create exactly the same soundstage as two loudspeakers interacting with a room. Bass reaches the ears but not the body. Angled drivers, spatial processing and crossfeed may move the image forward, but they do not turn headphones into loudspeakers.

My circumstances have changed over the years. I now own a serious speaker system with ELAC Vela 404 loudspeakers, but everyday life has again made dedicated listening space difficult.

Our living room is also used for my wife’s wellness business, so the audio equipment has to coexist with work, customers and family life. I describe that situation in Rethinking My Listening Space.

I also experimented with moving the STAX system into the bedroom. The sound could be excellent, but background noise, seating and sound leakage made the arrangement less practical than expected.

A STAX system may occupy less space than large loudspeakers, but it still needs a quiet and comfortable environment to show what it can do.

The Compromises You Notice After Living With STAX

No Isolation and Plenty of Sound Leakage

STAX earspeakers are open in both directions. You hear what happens around you, and other people hear much of what you are playing. They are unsuitable for commuting, a shared office or listening beside someone who wants silence.

Air conditioning, traffic, conversations and normal household noise can also mask the low-level information that makes an electrostatic system special.

A Dedicated Amplifier Is Mandatory

Buying the headphone alone is not enough. The amplifier or transformer interface must be included in the budget from the beginning. A tempting used headphone can become an expensive project once amplification and servicing are added.

The System Is Not Truly Portable

The SR-003 and compact battery-powered STAX units show that a smaller electrostatic system is possible. A full-size SR-007 or SR-009S setup remains stationary, with a dedicated amplifier, power supply, source and long proprietary cable.

Bass Is Fast but Not Always Physical

Good STAX headphones can reproduce deep and highly articulate bass. What they usually provide less of is the bodily impact associated with loudspeakers or powerful planar-magnetic headphones.

Listeners whose priorities are electronic music, hip-hop or the strongest possible kick-drum impact may prefer another design.

Older Equipment and DIY Amplifiers Need Care

Many vintage STAX headphones and amplifiers are decades old. Capacitors age, tubes wear out, pads deteriorate and dust protection can fail. Some replacement parts are no longer available, and not every repair shop is comfortable working with electrostatic drivers or high-voltage circuits.

My modified SRM-1/MK2 and recapped SRM-T1 show how well older units can perform after proper servicing. The humidity-damaged KGSSHV and the warranty repair required by the newer SRM-D50 illustrate the other side of long-term ownership.

Building an electrostatic amplifier can be extremely rewarding, but it also makes future diagnosis and repair the builder’s responsibility. High internal voltages make casual experimentation dangerous, and good documentation matters if somebody else may eventually have to service the unit.

STAX vs Modern Dynamic and Planar Headphones

When I first wrote this article, I had compared the SR-507 with several important conventional flagships, including the Sennheiser HD800, AKG K812 and a number of Audeze planar-magnetic headphones.

The STAX presentation sounded clearer and less mechanically constrained to me. The planars generally provided stronger bass impact, while the HD800 created a large soundstage but did not reproduce voices with the same effortless realism.

At a later Head-Fi meeting, I heard the SR-009, Focal Utopia and other high-end models. The Utopia impressed me with its clarity and dynamics and showed how far conventional headphones had progressed, but the experience did not remove my preference for electrostatics.

More recently, I have compared my STAX system with several modern alternatives.

Fostex T50RP With EQ

The current Fostex T50RP surprised me. Combined with a Qudelix 5K and careful EQ, it sounds far better than its modest price suggests. Its tonal balance can be adjusted effectively, while the planar driver provides good detail and bass control.

It does not fully reproduce the SR-009S’s openness, stage depth or realism with voices, but it demonstrates how close a well-equalized affordable headphone can come in overall tonal accuracy.

Fostex TH900

The TH900 offers stronger physical bass and a more immediately exciting presentation. It is an entertaining choice for music that benefits from impact and energy, but it is less neutral than the SR-009S and its closed construction does not create the same sense of air or depth.

Dan Clark Stealth and E3

The Dan Clark Stealth is technically impressive and provides the isolation that STAX completely lacks. I found it more convincing than the E3, whose midrange sounded somewhat hollow and artificial to me.

The Stealth did many things well, but it did not trigger the same immediate sense of hearing something fundamentally different that I experienced with my best STAX systems. Its major advantage is practical: it delivers very high performance in a closed headphone that can be used around other people.

What EQ Can and Cannot Do

EQ can bring different headphones much closer in tonal balance. It can correct bass level, upper-midrange energy and treble balance, but it cannot completely change the physical behavior of the driver, the enclosure, decay characteristics or spatial presentation.

A carefully equalized planar or dynamic headphone can sound remarkably similar to the SR-009S in frequency balance. The remaining differences become smaller, but they do not disappear entirely. For me, the SR-009S retains its advantage in voice realism, transparency, low-level detail and depth.

Buying a STAX System Today

When I first published this article, I recommended the SR-2170 system as the most affordable serious entry into STAX. It combined the SR-207 earspeaker with the small SRM-252 amplifier, sold for less than €1,000 through normal channels and could sometimes be imported from Japan for under €500.

That was genuine advice for the market in 2015. It should not be treated as a current product or price recommendation. The range has changed, import conditions are different and surviving older systems require more attention to condition and service history.

Budget for the Complete System

Do not spend the entire budget on the headphone and treat the amplifier as an afterthought. A less expensive Lambda with a suitable amplifier can be more satisfying than a flagship connected to the first unit you could still afford.

Listen Before Buying a Flagship

STAX models do not all share one tonal balance. The SR-507 was crisp and analytical, the Omega 2 MK1 was darker and fuller, and the SR-009S is more neutral and resolving. A higher model number does not guarantee that you will prefer the result.

Used STAX Can Be Excellent Value

I bought several of my best STAX components second-hand, including the Omega 2 and SR-009S. Used buying can make an otherwise unreachable system affordable, but condition matters more than age alone.

Check channel balance, background noise, cables, pads, headband, driver protection and amplifier service history. When possible, a used amplifier with a valid dealer warranty can be worth paying more for. The SRM-D50 repair would otherwise have become my financial responsibility.

My broader approach to buying expensive audio equipment second-hand is described in The Ultimate Guide on How to Shop for Luxury Hi-Fi.

Be Careful With Imports

Importing my SR-507 from Japan worked for me, but buyers should consider voltage requirements, taxes, warranty support and return costs. A low purchase price becomes less attractive if the headphone arrives with channel imbalance or the amplifier needs servicing overseas.

Decide How Much DIY You Really Want

A custom amplifier can provide exceptional performance and a rewarding construction project. It also creates long-term maintenance responsibilities.

Today, I am happy to let Andreas Rauenbühler build and support the Antares instead of constructing another large high-voltage amplifier myself.

Would I Buy STAX Again Today?

Yes, but I would approach the purchase more deliberately than I did during some earlier stages of the journey.

I would first decide which tonal balance I wanted and where the system could realistically be used. I would budget for the headphone and amplifier together, and I would no longer build another large high-voltage amplifier merely because I could.

A STAX setup needs a quiet place, a comfortable chair and enough freedom that sound leakage does not disturb somebody else. Without those conditions, a closed headphone may receive far more listening time even when it is not the technically superior option.

For my own listening, the SR-009S and Antares still justify the inconvenience. You can see the rest of the equipment surrounding them on my My Gear page.

Final Verdict

When I first heard a Lambda Pro in the late 1980s, I could not afford it. I only knew that I had heard something different.

That experience eventually led to a used SR-404 and SRM-313, a home-built High-Amp tube amplifier, another Lambda Pro, an imported SR-507, a modified SRM-1/MK2, a recapped SRM-T1, the tiny SR-003, my DIY KGSSHV, an Omega 2 MK1 and finally the SR-009S. After the KGSSHV failed, the amplifier journey continued through a used SRM-D50, an SRM-400S and ultimately the High-Amp Antares.

The journey was not a simple sequence of increasingly expensive components. The SR-507 was explicit and energetic, the Omega 2 darker and more physical, and the SR-009S more neutral, resolving and spacious.

The amplifiers taught me a different lesson. The KGSSHV showed what a serious DIY design could achieve, but its eventual failure also exposed the burden of maintaining one-off high-voltage equipment. The defective SRM-D50 demonstrated the value of buying used equipment with warranty coverage, while the SRM-400S confirmed that a technically adequate amplifier is not automatically one I will enjoy long-term.

Modern dynamic and planar headphones are better than ever. Some provide stronger bass, closed-back isolation, easier amplification and a far more portable system. EQ can narrow the tonal gap considerably.

I still return to the SR-009S when I care most about natural voices, acoustic instruments, spatial depth and the smallest musical details. That preference is not based on nostalgia or the novelty of high-voltage technology. It comes from the way a good electrostatic system seems to remove itself from the recording.

Decades after hearing that first Lambda Pro, STAX still gives me the closest thing I have found to listening through the equipment and directly into the recording.

Last updated: August 2026. All STAX headphones and amplifiers discussed in this article were personally owned, built or used by me unless clearly stated otherwise.