Stax SRM-500T
Hybrid Stax amplifier with 6FQ7 tube, dedicated to driving the brand's electrostatic headphones, with balanced circuit and electrostatic RCA output.
Description
The SRM-500T is an amplification driver unit dedicated to Stax electrostatic headphones, the only models capable of using this type of high-voltage output. It succeeds the SRM-006tS and adopts a hybrid architecture combining a low-noise FET input stage custom-designed by Stax with a 6FQ7/6CG7 vacuum tube output stage. This type of amplifier does not connect to speakers or conventional dynamic headphones: it exclusively powers electrostatic headphones via dedicated high-voltage RCA outputs.
The output stage relies on two 6FQ7 double triodes mounted without negative feedback, in a balanced circuit complemented by a four-gang potentiometer. The SRM-500T stands out through the addition of a power transformer dedicated to the low-voltage circuit, in addition to the conventional high-voltage transformer, which improves energy efficiency and sound quality compared to the brand's previous tube driver units. The frequency response extends from DC up to 90 kHz with an SR-L500 MK2, for a gain of 60 dB and harmonic distortion of 0.01% or less at 1 kHz under 100 Vrms. Maximum output voltage reaches 300 Vrms at 1 kHz, and input impedance is 50 kΩ on both RCA and XLR (two channels).
This type of amplifier is aimed at owners of Stax electrostatic headphones seeking tube electronics designed specifically for this technology, as an alternative to fully solid-state driver units. It will suit listeners attentive to the sound texture characteristic of tube stages, within a dedicated and carefully considered headphone listening setup.
Technical specifications
| Type | Hybrid DC driver unit, FET input + vacuum tube output |
| Vacuum tube | 6FQ7 / 6CG7 |
| Frequency response | DC - 90 kHz (with an SR-L500 MK2) |
| Gain | 60 dB |
| Harmonic distortion | 0.01% or less (1 kHz output / 100 Vrms) |
| Input impedance | 50 kΩ (RCA), 50 kΩ x 2 (XLR) |
| Maximum output voltage | 300 Vrms (1 kHz) |
| Dimensions (W x H x D) | 195 x 102 x 376 mm |
| Weight | 3.4 kg |
What to check before buying used
The four-gang potentiometer is worth checking at the end of its travel, where crackling or channel imbalance most often appears after many years of use. The two 6FQ7/6CG7 triodes are consumable wear parts whose condition can only be judged by listening, regardless of their purchase date. The high-voltage RCA outputs, incompatible with any headphones other than Stax electrostatic models, must remain clean and securely fitted to avoid any dangerous poor contact at these voltage levels.
Looking for this reference: SRM-500T ?
Tell us what you are looking for: our merchants are notified, and one of them may have it in stock.