STAX DA-80

Commentary

This is a stereo power amplifier developed by lowering the output power of the DA 300 and adopting the latest amplifier design method.

The DA-80 consists of two monaural power amplifiers in one chassis, and the power supply is completely independent of the transformer.

The first stage uses a low-noise dual FET as a current mirror load, the second stage cascade, and the last stage Darlington pure complimentary service system. All stages are A-class circuits designed with linearity in mind and ignoring the tonal variation caused by the output of the preamplifier due to the high input impedance.

The power supply section has a ± 8 power supply configuration. It passes through four silicon bridge diodes, two each from left and right independent transformers, and is smoothed by eight high-capacity electrolytic capacitors.
Class A push-pull power power stage is driven by a power supply with low internal resistance and low noise components using a large capacity 33,000 μ Fx4 electrolytic capacitor and a special capacitor with excellent Tan δ to supplement this. In addition, a 6,800 μ Fx4 electrolytic capacitor is installed exclusively for the pre-driver stage to minimize the influence from the power stage and stabilize the operation of the direct-coupled differential amplifier.

High-quality parts are carefully selected and used. Metal film resistance is used for the resistance of the signal handling part, and special materials with excellent tan δ are used for the capacitor. Also, the land of the substrate is devised to reduce DC resistance. By using parallel jumpers, extra inductance and resistance are prevented from entering the line through which the signal passes.
The speaker terminals are made by Herman H. Smith of the United States of America, which have low contact resistance and are gold-plated.

The driver unit and power unit are plug-in type in case of accident and can be replaced independently.

It is equipped with four protection circuits. In addition to output short-circuit protection, temperature protection, and speaker protection, it is equipped with excess input protection that protects the internal circuit when a signal of 50 V or more (attenuator 0 dB) is applied to the input terminal.
As soon as the temperature protection circuit and speaker protection circuit are activated, the power supply is turned off. The red pilot lamp remains lit and the power switch lamp goes off. In this case, the operation of the amplifier is restored by turning the power switch on again.
This protection circuit does not use a relay in the signal path, and is designed to stop the power supply to the circuit to prevent deterioration of sound quality.

Model Rating

Type	Stereo power amplifier
Circuit system	Class A operation DC amplifier Pure complimentary service method using the first stage FET Left and right independent ± 4 power supplies (total 8 power supplies)
Effective power	45W+45W
Power bandwidth	5 hz ~ 50 khz -3dB (THD 0.1%)
Total harmonic distortion factor (8 Ω at 45W output)	0.0025%(1kHz) 0.005% (DC ~ 10 kHz)
Damping factor	600 (1 kHz, 8 Ω)
Signal-to-noise ratio	100 dB or more
Input Sensitivity / Impedance	0.89V/100k Ω / 100 pF
Frequency response (at 1W output)	DC Operated : DC ~ 500 khz + 0 -3dB AC Operated : 3 Hz to 500 kHz + 0 -3dB
Gain	26.3dB
Load	2 Ω or More (Music Playback) 4 Ω or more (during test)
Slew rate	20 V / μ sec
Phase difference	+ 0 ° -3 ° (0 ~ 10 kHz)
Crosstalk	-90dB or less (1 kHz)
Maximum Input Voltage	50 V (Both AC/DC)
Power supply drift	± 3 mv (± 10%)
Time drift	± 25 mv (Stabilizes in about 10 minutes after switch is turned on)
Temperature drift	± 10 mv (0 ° C to 40 ° C)
Source drift	Undetectable
Operating temperature range	0 ° C ~ 40 ° C
Short circuit protection circuit	Operates at 2 Ω or less
Speaker protection circuit	Operates at approx. ± 5 v
Temperature protection circuit	Transistor case temperature : Operates at about 120 ℃
Idle current drift	After switch on : Approx. 130% Switch after turning off 10 minutes : 100%
Attenuator	0 db, -10dB, -20dB, - ∞
Semiconductor used	Dual FET : 2 units Dual Transistor : 2 Transistor : 27 Bridge Diode : 4 Diode : 20 pcs
Power supply voltage	100V/117V, ± 10%
Power frequency	48 Hz to 62 Hz
Power consumption	320W
External dimensions	Width 437x Height 163x Depth 407 mm
Weight	19.5kg