STAX SR-1

Commentary

Stacks' first condenser ear speaker.

The structure of the SR-1 is a push-pull type among capacitor types.
The principle is that there are two fixed electrodes with a small gap between them, and a metallized thin film is stretched with moderate tension between them. This thin film is attracted to the fixed electrode by the attraction force of static electricity.

The housing is an open type, and the sound emitted from the speaker is close to the Chinese character of listening.
A DC voltage of about 200 V (150 V in the initial state) is required for use, a signal voltage of about 150 V (100 V to 150 V in the initial state) is required for use, and a capacity load of 120 pF per amplifier is required for the load of the amplifier.
To satisfy this condition, connect a STAX adapter to a commercially available stereo main amplifier, or use a dedicated amplifier. The dedicated amplifier at that time used 12AU7 for the final stage tube and used a resistance-capacitance coupling method. Therefore, no transformer or choke can be put in, so you can enjoy pure sound.

There were two types of adapters : SRD-2, which is connected to the speaker terminal of the main amplifier, and SRD-1, which is taken out from the plate of the output tube.

Model Rating

Type	Headphone
Connection plug	20 φ x27mm Black Case
Connection outlet	2.4 φ x 13 mm with 6 Legs 16 φ x10.5 mm, Front Flange 18 φ x24mm, Lock Washer 22 mm φ
Rubber pad	Outer Diameter 80 φ, Inner Diameter 60 φ, Height 20 ~ 30 mm, Soft Foam Rubber
Retaining fitting	Head Type Total Length 420 ~ 408 mm Variable
Left and right labels (changed from September 1964)	For left ear : internal gray, cord gray For Right Ear : Internal Red, Cord Ash Red Mixed Color
Electric capacity	About 120 pf for one ear (including attached cord 1.5m)
Polarized voltage	Approximately 150 VDC (Initial Type) Approximately 200 VDC
Frequency characteristic	20 Hz ~ 20 kHz (Initial Type) 30 Hz to 20 kHz
Weight	320g (Holding Metal Part 85g, Cord 75g)