Type: push-pull electrostatic, oval sound element, rear open-air type enclosure

Frequency response: 7 – 41,000Hz

Electrostatic capacitance: 110pF (including attached code) Impedance: 145kΩ (including attached cable, at 10kHz) Sound pressure sensitivity: 101dB / input 100Vr.m.s. / 1kHz Bias voltage: 580V DC

Ear pad: high-quality artificial leather (for SR-L300 only)

Cable: parallel 6-strand, 2.5m full length, low-capacity special wide OFC cable

Weight : 448g (including attached cable), 322g (without cable)

For more information check out the following.

https://staxheadphones.com/products/earspeaker-of-advanced-lambda-series-2

SRM-400S (Semiconductor Driver)

SPECIFICATIONS

All-stage FET configuration DC amplification driver unit

Frequency response: DC - 90kHz (with one SR-L500 MK2)

Gain: 60dB

Harmonic distortion: 0.01% or less (1kHz/100Vrms output)

Input impedance: 50k Ω (RCA), 50k Ω x 2 (XLR)

Maximum output voltage: 400Vrms (1kHz)

Bias voltage: DC 580V

Operating temperature / humidity: 0 to 35 degrees celsius / less than 90% (non condensing)

Input terminal: RCA x 1, XLR x 1(mutual exclusion input)

Output: RCA parallel output terminal

Power consumption: 30W

Dimension: 195 (W) x 102 (H) x 376 (D) mm (maximum protruding portion included)

Weight: 3.4kg

For more information check out the following.

https://staxheadphones.com/products/srm-400s-vacuum-tube-driver-unit-for-earspeakers

A look Inside

In this review both Electrostatic and drive units are reviewed. Let's start with the simpler of the two, the SR-L300 Ear Speakers.

Built mostly of plastic, this result is a fairly lightweight experience. Additionally, artificial leather is used for the headband, eliminating any hotspots. The five-pin pro cable is permanently attached to the Earspeakers, but lengthy.

If I had to criticize the design of the L300s, the ear padding is a bit thin.

Even though the L300 is the “starter pair” of Earspeakers in the Lambda series, it does not seem as such. As it sounds full-bodied and rich.

We now move to what I would call the true star of the show, the SRM-400S drive unit which is bundled with the L300s, but can power a variety of other STAX Earspeakers.

The 400s is the latest revision of the drive unit. “…the successor model of the SRM-353X” SRM-400S. To learn more about the 400s follow the link.

https://staxheadphones.com/products/srm-400s-vacuum-tube-driver-unit-for-earspeakers

Using only critically matched for this FET-based design. As a result, a quiet noise floor is any noise floor.

There is no noise bleed, even at zero, and the channel balance is matched as well.

New transformers improved transformers were used in the 400s as well over the previous version.

“The new chassis which is more rigid than the conventional model is installed. The chassis has a hybrid structure using a lot of non-magnetic aluminum and further reduces the effect of the environmental noise factors such as vibrations.”
SRM-400S Semiconductor Driver Unit – STAX Headphones

RCA and XLR are wired in series in the 400s, for both input and outputs.

On the front of the unit from left to right are the power button, parallel outputs, and a substantial volume knob. I have one small complaint about the volume knob, but I will talk about this in the suggestions section.

On the Rear, left to right dual XLR outs, a selector switch to select from RCA or XLR out, RCA outs, and an IEC power inlet.

Play the music

For this review, I used the following gear, Roon Nucleus Plus, a two-year-old PC, iFi NEO iDSD 2 DAC, and Qobuz for a source.

Time to return with “The Returner” by Allison Russell. In a word, beautiful. This track shines on this the L300s. Vocals shimmer, the bass is tight, the piano is natural, oh and did I say vocals are sweet? Then there are the strings which are fantastic as well. This song simply exudes why STAX is so good!

It is time to shine on with “Shine On You Crazy Diamond (Pts. 1-5).” We start with the classic synthesizers that immerse us into this song and drip with emotion as the guitar begins to erupt. The guitar is more airy and carries, so sweet.

This song has a different feel from the Electrostats. Much deeper, more resolving, and quicker, though at the same time, but less low-end than traditional earphones.

Want to experience a life-like performance then listen to Otis Taylor on “Jump Jelly Belly.” This is one of the best performances that I have heard in quite a long time, and the L300s exemplify this.

The STAX system is the first true taste of Electrostatics, and it is fantastic. So musical, now see, why people love the sound. There is a sound, that is layered, highly resolving, fast, and slightly bass-light, but natural.

Suggestions

This was a difficult one as there was only one I could think of.

The only one that I could have was padding for the earcups. If there were more earcups, then I think these would be almost perfect.

Closing thoughts

The STAX SRM-400S $1,299 /SR-L300 $455 respectively, are well worth it and I can highly recommend them. Just keep in mind that the power unit does take up some desk space.

Gear Used

Roon Nucleus Plus

Roon

Qobuz

PC (Windows 11)

NEO iDSD 2

Music Used

The Returner - Allison Russell

https://open.qobuz.com/track/211988154

Shine On You Crazy Diamond (Pts. 1-5) - Pink Floyd

https://open.qobuz.com/track/47683562

Jump Jelly Belly - Otis Taylor

https://open.qobuz.com/track/204622598