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Stax - International SRM-500T Vacuum Tube Driver Unit For Earspeakers
Complete model change for the first time in 11 years
The SRM-500T, which follows the numerical sequence of the SRM-700 series, is the successor model to the vacuum tube driver unit SRM-006tS and is 11 years in the making.
STAX custom-made low-noise DUAL FET is used for the first stage, and high-voltage double triode 6FQ7 / 6CG7 is used for the output stage. While following the traditional circuit design which is perfect for STAX vacuum tube drivers, we have improved the efficiency of the power supply and further improved the sound quality.
In addition to the conventional power transformer for the high voltage circuit, the newly designed power transformer with the winding for the low voltage circuit is installed in SRM-500T. By adopting this low-voltage winding, the efficiency of the power supply has improved, and compared to conventional vacuum tube driver units such as the SRM-006tS, power saving and improved sound quality have been achieved.
In addition, a new chassis with increased rigidity compared to SRM-006tS has been adopted. The hybrid structure, which uses a lot of non-magnetic aluminium, further suppresses the effects of physical external noise such as vibrations. The inputs are RCA and XLR, the mutual exclusion inputs. The custom made concentric dual volume knob which is common to STAX products and RCA PARALLEL OUT functions are installed same as the conventional driver units. All electric components are strictly selected considering the environment. Also the sound quality and the performance is improved. The complete DC ampli er con guration that the signal circuit includes no coupling condensers is one of the biggest traditional features.
The clear and highly transparent sound, a feature of the vacuum tube circuit and the warm and wide sound texture are maintained and the thickness of the low-mid range is brushed up.
Therefore we recommend the SRM-500T in combination with the advanced lambda series earspeakers (SR-L300/SR-L500 MK2/SR-L700 MK2).
- Type: FET + vacuum tube output hybrid DC amplifier configuration / driver unit
- Vacuum tube : 6FQ7 / 6CG7
- Frequency response: DC to 90kHz (when using one SR-L500 MK2)
- Gain: 60dB
- Harmonic distortion rate: 0.01% or less (at 1kHz / 100V r.m.s. output)
- Input impedance: 50kΩ (RCA), 50kΩ x 2 (XLR)
- Maximum output voltage: 300V RMS (1kHz)
- Bias voltage: DC 580V
- Operating ambient temperature / humidity: 0 to 35 ° C / 90% or less (however, no condensation)
- Input: RCA x 1 XLR x 1
- Output: RCA out
- Power consumption: 38W
- Dimensions: 195W x 102H x 376Dmm (including protrusions such as knobs)
- Weight: 3.4kg
- Country of origin: Japan
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Stax SRM-500T Vacuum Tube Driver Unit For Earspeakers
The diminutive SRM-500T is a purpose-built hybrid FET + vacuum tube energizer that brings Stax's electrostatic character to a more accessible price. Reviewers at AUDIOKEY REVIEWS (K. E. Heartsong) praise its transparent, natural treble, lush midrange and nimble transient speed, yielding a three-dimensional soundstage with precise imaging. It trades the deepest sub-bass and the absolute extremes of flagship models for refined control, resolution and lively dynamics—making it an excellent match for SR-L-series earspeakers. The compact, well-built chassis and straightforward front/rear connectivity suit dedicated electrostatic systems. For listeners entering the Stax ecosystem, the SRM-500T delivers musicality, technical poise and strong value as an entry-level energizer.
Pros
- Transparent, natural treble and a lush, well-textured midrange that preserves timbre and detail.
- Excellent transient speed, dynamics and a spacious, well-defined soundstage for electrostatic headphones.
- Compact, robust build with focused connectivity (balanced XLR and single-ended RCA inputs, dual 5-pin outputs).
- Strong value as an entry-level Stax energizer that brings flagship DNA to a lower price point.
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Cons
- Bass extension and slam do not match higher-end Stax models—powerful, dramatic low-end passages can be wanting.
- Does not reach the absolute treble extremes of flagship siblings (some compromise for the price point).
- Ships with basic power cord and interconnects; reviewer recommends upgrading cables for best results.
Sound Quality
91/100
The SRM-500T is described as having excellent transient speed and lively dynamics, second only to higher-priced Stax siblings and excellent when paired with electrostatic headphones. Reviewers do note that the unit can leave extremely powerful, dramatic bass passages wanting compared to top-tier models, but overall punch, speed and micro-dynamics are very strong.
Noise Floor
87/100
Although the SRM-500T uses a hybrid FET + vacuum tube output stage (6FQ7/6CG7), reviewers make no mention of audible hiss or problematic background noise; they emphasize transparency appropriate for electrostatics. This indicates the FET/tube design delivers tube-like musicality without raising the noise floor to problematic levels for electrostatic earspeakers, so the unit is very quiet and suitable for sensitive electrostatic headphones even if reviewers stop short of calling it 'reference-level' silent.
Headphone Compatibility
89/100
Designed specifically as a driver/energizer for Stax electrostatic earspeakers (specs reference DC–90kHz with SR-L500 MK2 and 300V RMS maximum output), it pairs exceptionally well with electrostatic headphones. It is purpose-built for that ecosystem and delivers excellent performance there, but it is a specialist unit rather than a generalist amp for all dynamic/planar headphones.
Build Quality
90/100
Reviewers describe the SRM-500T as diminutive yet well executed and built to last, continuing Stax's tradition of robust energizers. The compact, well-made chassis and thoughtful front/back panel layout (dual 5-pin outputs, large volume knob) support a high build-quality impression.
Features Connectivity
84/100
Front-panel dual 5-pin electrostatic outputs and a large volume control, plus rear-panel balanced (XLR) and single-ended (RCA) inputs and a parallel out, give a practical and focused set of features for an electrostatic driver. It lacks digital inputs, internal DAC, multiple gain stages or modern streaming features, so feature score is good for its class but not high for a full-featured desktop DAC/amp.
Value for Money
90/100
Reviewers call the SRM-500T an 'entry-level' Stax energizer and recommend it highly for those new to electrostatics, stating one would have to spend a great deal more to approach or better it. That language and the positive recommendation justify a strong value rating for its target audience and price point.
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