YAMAHA A-6

Commentary

A stereo pre-main amplifier that achieves both high quality and high power with a pure current servo amplifier and X power supply.

The power supply section is equipped with X power supply by Phase Angle Control circuit.
The X power supply is a precise feedback circuit from the secondary side to the primary side of the power supply. When the supply voltage on the secondary side tends to decrease due to changes in the output signal, etc., it is detected by a voltage comparison amplifier, and high-speed feedback is applied by a photocoupler to the primary side. This enables the operation of the TRIAC (AC control element) inserted in the primary side of the transformer to be controlled.
This TRIAC uses signals from the secondary side to control the conduction phase angle of the voltage waveform flowing through the transformer to keep the secondary side power supply voltage constant at all times. This realizes a highly stable constant voltage power supply that is unaffected by fluctuations in load and primary voltage. In addition, by controlling the energization time of the transformer, the loss of the iron core can be reduced, and the winding of the coil is also reduced, so the transformer is reduced to less than 1/2 of the conventional size.
In addition, compared with conventional switching power supplies, the circuit is extremely simple and reliable, and noise characteristics are excellent because no high frequency is used.

The equalizer amplifier is equipped with a pure current servo amplifier.
In principle, the signal current flows only in the output loop, and the power supply circuit is always designed to have a constant current flow. Installing a pure current servo amplifier, the influence of nonlinear elements in the power supply circuit is suppressed.
In addition, the circuit uses a High-gm FET differential input stage and ICL to realize more realistic reproduction.

It is equipped with a DISC switch. When the DISC switch is pressed, the selector switch jumps regardless of the position of the built-in selector, enabling pure playback.

Equipped with a Phono selector, it is compatible with both MM and MC.

Equipped with a main direct switch, tone control, high filter and loudness are removed from the signal path, and the signal can be directly input to the DC amplifier from an equalizer or tuner.

Model Rating

Type	Pre-main amplifier
Effective output (20 Hz to 20 kHz, distortion 0.01%)	100W+100W
Power bandwidth	10 Hz ~ 50 kHz (50W, Distortion 0.02%)
Damping factor	55
Input Sensitivity / Impedance	Phono MM : 2.5mV/47k Ω Phono MC : 250 μ V/100 Ω Tuner : 150mV/47k Ω
Maximum Allowable Input (Distortion 0.01%)	MM:180mV MC:18mV
Output Voltage / Impedance	Rec out : 150mV/550 Ω
Frequency Response (Main Direct On)	Tuner → SP Out : DC ~ 100 khz + 0 -2dB
RIAA deviation	20 Hz to 20 kHz ± 0.2 dB
Total harmonic distortion rate (20 Hz to 20 kHz)	MM → Rec Out (5 V) : 0.003% MC → Rec Out (5 v) : 0.006% Tuner-to-SP Out (50W) : 0.005%
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1)	Tuner → SP Out : 0.002%
Signal-to-noise ratio	Phono MM:86dB Phono MC:70dB Tuner:103dB
Input reduced noise	Phono MM:-138dBV Phono MC:-147dBV
Residual noise	183 μ V
Channel separation (Input Short, 1 kHz, Volume-30dB)	MM → SP Out : 70 dB
Tone control	Bass : ± 10 dB (20 Hz) Treble : ± 10 dB (20 kHz)
Filter	12dB/oct, 10 kHz
Continuous maximum correction amount	20 dB (1 kHz, sound correction curve)
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption	165W
AC outlet	Power switch interlock : 2 systems Power switch not linked : 1 system
External dimensions	Width 435x Height 112x Depth 365 mm
Weight	9.1kg