STAX SRM-727II DRIVER
New vistas for the non-feedback output stage
The first performance feature required of audio equipment is the capacity to convert air vibrations into sound waves so that the slightest signal can be appropriately heard by the ear. This means that an essential condition of the vibrating medium, i.e. the diaphragm, in the speaker which constitutes the system of conversion from electrical signal to air vibration is that it needs to be as light as possible. Divided vibration, which is unavoidable in the case of point drive, is possible, as is also ultra-miniaturization if total drive is possible. Moreover, if headphones are used, there will be reduction in the mass of air that needs to be driven, creating a more ideal situation.

The electrostatic (condenser) type is the system that comes closest to this ideal. STAX refers to speakers of this type as “earspeakers” and has continuously sought for the ideal form. Since a dedicated unit is needed for drive purposes, the development of such units is equivalent to the pursuit of high sound quality in the electrical signal system. The matching drive system and the amplifier system are used for driving electrostatic speakers, and in the case of amplifiers it is possible to build circuits by means of vacuum tubes. In the case of electrical signal systems too, it is generally known that sound quality varies extensively depending on the circuit configuration, parts, etc. Which should be selected? There is also the element of musicality that needs to be taken into consideration when determining the sound that is the be-all and end-all of audio.

The new SRM-727II employs semiconductor output drive stage and non-feedback (NON-NFB) output stage for the first time ever in a STAX driver unit. A pure balance DC amplifier configuration is used for the large current emitter follower Class A output stage. A significant increase in dynamic range especially in the upper frequency has been achieved. A high level of sound purity is achieved through the simple two-stage amplification circuit with low-noise FET input stage. This is a brand new driver unit that opens up new vistas for the sense of mass and textural expression supported by a virtually unparalleled degree of resolution, a natural sense of openness, and a powerful power section.

Features
The electrostatic method is a playback method which involves the installation of drive electrodes on either side of a high-polymer film diaphragm with a thickness of only a few microns into each of which a plus signal and a minus signal are fed. This means that XLR connection with a pure balance output CD player makes it possible to listen to the original sound permitted by the balance system without a conversion circuit.

The output stage has been incorporated by newly developing a non-feedback (NON-NFB) large current emitter follower Class A amplification circuit. This makes it possible to achieve a much more vivid and dynamic sound quality.
The emitter follower at the output stage makes it possible to achieve lower impedance. A major expansion in dynamic range in the upper frequency has also been achieved.

DC amplifier configuration without the use of a coupling condenser.
A high sound quality, low noise FET is used at the input stage with a simple two-stage amplifying circuit. A natural and pure sound quality with high information quantity is realized.

When connecting your favorite attenuator or pre-amplifier, a direct switch that avoids duplication of the volume unit is included.
Careful selection of parts with high consideration on sound quality, performance, and the environment.
In order to avoid magnetic distortion, the chassis is made of aluminum materials, thereby contributing to purity of sound.
Amplification is set at a low level, thereby facilitating subtle adjustment of volume during XLR input and when using high-output CD players, etc.

Parallel output terminals (RCA) are included to enable the signal to pass through.
A new panel face has been designed with rounded corners and a silver brushed finish.
Earspeakers of PRO bias (5-pin) type can be used.

Control functions are restricted to the volume, and the input uses a single selecting system between RCA or XLR. This is a drive unit for exclusive use with earspeakers with emphasis placed first and foremost upon purity.