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Stax - International SRM-700S Semiconductor Driver Unit #1

Stax - International SRM-700S Semiconductor Driver Unit variant 1

Stax - International SRM-700S Semiconductor Driver Unit variant 2

Stax - International SRM-700S Semiconductor Driver Unit variant 3

Stax - International SRM-700S Semiconductor Driver Unit

Name: Stax - International SRM-700S Semiconductor Driver Unit
Brand: Stax - International
SKU: driverunitforearspeakerssrm700s
Rating: 4.5 (3 reviews)

View at Stax - International

XLR Input

Balanced Output

All semiconductor driver unit that has adopted custom-made low-noise dual FET at the first stage, and for the first time in STAX driver unit history J-FET has been employed at the second stage. The output of J-FET excellent in low-noise amplification as well as large current emitter follower circuit brings out the full performance of earspeakers. Even the music source with much high-frequency ingredients can easily be driven. The driver unit pursues an exact reproduction of musical details.

Gramophone Dreams #102: Stax SR-007S Earspeakers

Stax's SRM-700S driver unit is all JFET, and it is so transparent I swear that in the quiet passages I could hear its JFETs flowing current. Which suggests the 700S is a simple, naturally clean design with minimal feedback.

Listening to Serge Gainsbourg's Histoire de Melody Nelson, my attention kept focusing on how Serge and Jane Birkin pronounced their words. With the 700S powering the 007S, each word had its own shape and internal structure.

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Overall Score 90/100

Deliciously Crispy

Stax SRM-700S Semiconductor Driver Unit

Stax SRM-700S Semiconductor Driver Unit puts electrostatic detail and scale front and center with exceptional transparency and a cavernous soundstage. K. E. Heartsong and Vedran Simunovic highlight its speed, deep yet controlled bass, and crystalline treble. The SRM-700S delivers authoritative dynamics and an ultra-low noise floor that teases out microdetails and wide imaging, making voices and instruments palpably present. Built as a focused, all-analogue energizer with RCA/XLR inputs, dual 5‑pin outputs and a precise volume/balance control, it pairs best with Stax-style electrostatic headphones. Its compact, well-made chassis and transformer-based supply underline enduring build quality. Ideal for critical listeners who want a dedicated electrostatic solution, the SRM-700S offers class-leading transparency and headroom that reviewers say justifies its place in a high-end headphone rig.

SoundStage! Australia

"The SRM-700S with electrostatic headphones leave electrodynamic headphones firmly in the dust and challenges even the best of speakers and setups with their accuracy and lifelike performance."

AUDIOKEY REVIEWS

"The STAX SRM-700S is an extremely capable earspeaker energizer that, simply, must be heard!"

Pros

Exceptionally transparent presentation with a vast, three-dimensional soundstage and precise imaging.
Powerful, controlled bass and lively PRaT — tight low end with strong transient speed and musical drive.
Very low noise floor and excellent headroom — resolves pianissimos and thunderous crescendos without strain.
Robust, purpose-built construction and dedicated electrostatic connectivity (RCA/XLR inputs, dual 5‑pin outputs) for reliable long-term use.

Cons

Limited to electrostatic (5‑pin) headphones — cannot drive conventional dynamic or planar models.
Not suited for casual/background listening — its revealing nature exposes recording flaws and rewards focused, critical sessions.
Feature set is intentionally focused (no built-in DAC or streaming, and no modern consumer headphone jacks), so it requires upstream source gear.

Sound Quality

92/100

Multiple reviewers praise the unit's huge amplification, headroom and transient speed — terms used include “ample dynamic range,” “commanding, potent, and explosive,” and strong PRaT (pacing, rhythm and timing). It handles quiet pianissimos and thunderous crescendos without strain, giving lively, engaging playback.

Noise Floor

91/100

Both reviews emphasize very low noise and profound silence (e.g., “very low noise,” “profound silence,” “silence between word and note”), making the SRM-700S well suited to the extreme sensitivity of electrostatic headphones. No reviewer reports audible hiss, and the J-FET stage is noted for its low overall noise.

Headphone Compatibility

84/100

The SRM-700S is purpose-built for electrostatic headphones (dual 5-pin outputs) and will drive any Stax-style electrostatic effortlessly, so within that ecosystem compatibility is excellent. However, it cannot be used with conventional dynamic or planar headphones, which limits versatility compared with generic headphone amps.

Build Quality

90/100

Build is described as very well executed and durable, with a transformer-based power supply and internal heatsinks contributing to its 6.3 kg mass. Reviewers note the clean, straightforward design and quality execution typical of Stax energizers.

Features Connectivity

84/100

Connectivity is focused and practical: RCA and XLR inputs, RCA parallel/pass-through outputs, and dual 5-pin electrostatic headphone outputs; front-panel volume with split/balance is useful. There is no built-in DAC, streaming, or modern headphone jacks (4.4mm/4-pin XLR), so features are strong for a dedicated electrostatic energizer but not expansive.

Value for Money

90/100

Reviewers give positive value opinions (e.g., “pinnacle of sound reproduction,” “highly recommend,” and an editor award), indicating the price is justified for buyers seeking electrostatic performance. Regional price mentions vary (AU$5,900 in one review; $3,400 in another), but sentiment is that the SRM-700S delivers performance commensurate with its asking price within the electrostatic category.