Although there is a feeling of use such as scratches and dirt, it is in a state where there is no problem in normal use.
Stereo pre-main amplifier with Class-B-Class-A operation switchable main amplifier.
The main amplifier uses an all-stage direct-coupled pure complementary OCL circuit that eliminates interstage capacitors.
Furthermore, high stability is obtained by using two stages of differential amplifiers and a bias stabilization circuit with transistors, and FETs are used in the bias circuit of the first-stage differential amplifier to obtain ideal bias characteristics due to their constant-current characteristics.
The power stage operation system is switched between Class-B and Class-A, allowing the user to freely select between the stable power of Class-B and the low distortion of Class-A.
The power supply section uses a large core power transformer with excellent regulation, 18000μF x 2 capacitors, and a large-capacity rectifier diode with a surge current of 250A.
In addition, a separately set constant voltage power supply is used to drive all stages except the power stage to improve the overall stability of the amplifier.
The protection circuit has two built-in stages, one for power transistors and the other for speakers.
The power transistor protection circuit is a quick-acting system that responds immediately to overloads on the order of μS. If the load drops below 2 ohms or the output terminals are shorted, the protection circuit instantly makes a differential movement to prevent problems. Since this circuit is an input limiter, playback is not interrupted even when the protection circuit is activated, only the output power is reduced.
The speaker protection circuit is based on Yamaha's original circuit system. If the DC voltage at the output terminals exceeds ±2V, the relay instantly makes a differential motion to shut down the signal path to the speakers. The relay automatically recovers when the voltage falls within ±2V, and since it also serves as a power muting circuit, there is no shock noise caused by rush currents when the power switch is turned on.
The first stage of the equalizer amplifier uses FETs in the SRPP method, which greatly improves the secondary distortion compared to the single method, since FETs have the advantage that the pulse noise is much lower than that of transistors, and the noise figure decreases as the signal source impedance increases.
In addition, the high supply voltage of +50V and the SEPP output stage, which allows for low output impedance, provide high output power with low distortion and a generous dynamic margin.
For the equalizer element, a combination of metal film resistors (±1% error) and styrene capacitors (±1% and ±2% error) are used, and a tantalum capacitor is used to minimize leakage current and ageing.
The Phono 1 circuit is equipped with an input impedance switching switch, allowing the load impedance of the cartridge to be adjusted to the optimum value. It also has a built-in head amp for MC cartridges, allowing direct connection of MC cartridges without a step-up transformer.
The function switch is mounted on the equalizer board, and external noise countermeasures are taken by means of wiring and a shielded case to achieve higher sound quality.
The tone control circuit uses the Yamaha method of mixing NF and CR types with a 3-stage direct-coupled amplifier. Careful selection of low-noise transistors minimizes residual noise and achieves high SN and low distortion.
In the Tone Defeat position, the circuit operates as a flat amplifier.
The filter circuit consists of a 3-stage direct-coupled amplifier with emphasis on phase characteristics and distortion rate.
The cutoff frequency of both the low and high filters can be switched in two steps.
The loudness circuit employs a continuously variable continuous loudness control with a dedicated loudness volume to allow adjustment based on the actual listener's ear.
It is equipped with a pre-main coupler that allows the preamplifier and main amplifier to be used separately from each other.
Audio muting is provided.
An amplifier dedicated to microphones is provided to prevent deterioration of sound quality caused by switching the time constant of the equalizer.
Model Pre-Main Amplifier
<Main amplifier section
Circuit method Class B/Class A operation switchable, all-stage direct-coupled pure complementary SEPP OCL circuit
Dynamic power (IHF) Class-B operation: 200W (8Ω)
Effective power
In dual-channel operation
20Hz to 20kHz: 15W+15W (8Ω, Class-A operation)
85W+85W (4 ohms, Class-B operation)
70W+70W (8Ω, Class-B operation)
1kHz: 15W+15W(8ohm, Class-A operation)
100W+100W (4 ohms, Class-B operation)
75W+75W (8Ω, Class-B operation)
Single-channel operation 1kHz: 15W/15W (8Ω, Class-A operation)
100W/100W (4 ohms, Class-B operation)
80W/80W (8Ω, Class-B operation)
Total Harmonic Distortion
Class-A operation: 0.1% or less (at RMS output)
0.02% or less (at 1W output)
Class-B operation: 0.1% or less (at RMS output)
0.04% or less (at 1W output)
Intermodulation distortion
(70Hz:7kHz=4:1)
Class-A operation: 0.1% or less (at RMS output)
0.05% or less (at 1W output)
Class-B operation: 0.1% or less (at RMS output)
0.05% or less (at 1W output)
Power bandwidth
(IHF, both channels driven) Class A operation: 5Hz to 100kHz
Class-B operation: 5Hz to 50kHz
Frequency response 10Hz to 100kHz +0 -1dB
Input sensitivity/impedance Class-A operation: 330mV/40kΩ
Class-B operation: 775mV/40kΩ
Output terminals: 3 speaker terminals
Headphone jack: 4Ω to 16Ω
Damping factor 70 (1kHz, 8Ω)
SN ratio (IHF, A-network) 100dB
Residual noise 0.8mV (pre + main amp, 8Ω)
<Preamplifier section
Circuit method Equalizer amplifier: FET SRPP input, Tr SEPP output 6-jewel amplifier
Microphone amplifier: 2-jewel direct-coupled amplifier
Control amp: 3-jewel direct-coupled amp with intermediate emitter follower
Input Sensitivity/Impedance Phono1 MC:200μV/100Ω
Phono1: 3mV/50kΩ, 100kΩ
Phono2:3mV/50kΩ
MIC:2.5mV/50kΩ
Tuner, AUX1, 2, Tape PB A, B:120mV/40kΩ
Output level/impedance rec outA, B:120mV/2kΩ
pre out:775mV/2kΩ
Phono maximum allowable input (1kHz) 310mVrms(870mVp-p)
Frequency Response Phono(RIAA deviation):30Hz to 15kHz ±0.2dB
MIC: 20Hz to 20kHz +0.5 -2dB
Tuner, AUX, Tape PB: 10Hz to 50kHz +0.5 -1dB
SN ratio Phono1 MC:70dB
Phono1, 2 MM:80dB
MIC:70dB
Tuner, AUX, Tape:90dB
Tone Control Bass: ±15dB(50Hz), Turnover frequency: 250Hz, 500Hz
Treble: ±10dB(10kHz), turnover frequency: 2.5kHz, 5kHz
Filter Low: 20Hz/70Hz, 12dB/oct
High: 6kHz/12kHz, 6dB/oct
Loudness control Continuous loudness equivalent to the loudness curve
Audio muting -20dB
<Overall
Power supply voltage AC100V, 50Hz/60Hz
Power consumption Rated:250W
Maximum: 420W
AC outlets Power switch interlocked: 2 lines, max. 200W
Power switch not interlocked: 2 systems, max. 200W
Dimensions: W436 x H144 x D323mm
Weight 15.5kg