Audio Database
SA-20
Commentary

A stereo power amplifier developed as an advanced equipment of SA-12 which combines vacuum tube and MOS-FET.

In the counter point amplifier, we pay attention to the merits of voltage-controlled amplification which is a characteristic of vacuum tubes. By using MOS-FET as the same voltage-controlled デバインス, large output can be efficiently extracted without losing the concept of the tube ball-type voltage-controlled amplification.
The SA-22 uses a twin triode 6DJ8 with low internal resistance and excellent linearity for the first and second voltage amplification stages and driver stages. The driver stage uses a cathode follower circuit with a constant current load to achieve further linearity and low distortion.

MOS-FET is used for the output stage. By removing the output stage from the NFB loop, there is no need to worry about oscillation caused by inductance of the speaker or network under any load.

The power supply section employs a large power transformer of 1 kVA in an independent configuration on the left and right sides. The power is rectified by 6CA4 and supplied to each section through a transistor-type ripple filter.

DC ignition is used for the heater circuit.

BTL connection is possible by switching the switch on the printed circuit board, and the highly reliable 6DJ8 phase inverter is used.

It uses high-quality audio parts that emphasize sound quality such as Rodenstein's metal film resistor and WIMA metalized polypropylene film condenser.

In addition to the silver model, there was a black model.

Model Rating
Type Stereo power amplifier
Effective power
SA-20 stereo


SA-20/20 Strap mono


SA-20/20 Bridge mono		 640W (2 Ω load)
420W (4 Ω load)
220W (8 Ω load)
760W (2 Ω load)
460W (4 Ω load)
220W (8 Ω load)
Deprecated (2 ohm load)
700W (4 Ω load)
600W (8 Ω load)
Frequency characteristic 1.2 Hz ~ 200 kHz (8 Ω Load)
Rise time 0.6 μ sec (8 Ω Load)
Total harmonic distortion factor 0.05% or Less (1W, Effective Output)
Cross modulation distortion factor 0.025%(CCIF)
0.02%(DIM200)
0.018% (SMPTE, 1W, 8 ohm Load)
SN ratio (input short) 84 dB (400 Hz to 80 kHz, no acoustic compensation, stereo, 8 Ω, 1W)
Damping factor 60 (8 Ω Reference)
Input impedance 100k Ω, 100 pf
Vacuum tube used 6DJ8 Audio Tube : 5 pieces
6CA4 Rectifier Tube : 1
Power consumption 260W (idle)
External dimensions Width 483x Height 170x Depth 483 mm
Weight 25kg