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HA-8700
Commentary

A pre-main amplifier developed by applying the know-how obtained with HMA 9500 to pre-main.

Power MOS FET, a newly developed new power amplifier, is adopted.
The power MOS FET achieves a switching speed of 0.05 μ sec and an amplification factor of 1 MHz (-2dB) in frequency characteristics, which is more than one order of magnitude higher than that of conventional bipolar transistors. The power MOS FET achieves a power gain of 85 dB at 100 kHz in bare characteristics, provides stable negative feedback even at 100 kHz, and achieves excellent push-pull operation even with class B circuit configuration because of its high switching speed.

In order to realize the performance of this power stage, a 3-stage power circuit with small phase change is adopted. In order to further improve low-frequency characteristics, a power supply section using a DC amplifier configuration, left and right independent power supply with excellent dynamic characteristics, and high-quality large-capacity capacitor is mounted.

The gain of the main amplifier is increased from 29 dB to 45 dB, and a main direct switch is used to connect the main amplifier directly to the output of the equalizer amplifier.
It is also possible to be used to reduce the gain of the main amplifier to the gain when the main direct is off.

All stages of the DC amplifier configuration is adopted in which capacitors are removed from the inlet of each stage of the head amplifier, equalizer amplifier, preamplifier and main amplifier and from the negative feedback (NFB) loop.
As a result, phase and response characteristics have been greatly improved, and low-frequency characteristics and transparency in mid-range and high-range areas have been improved.

The equalizer amplifier section consists of three stages : a cascade differential current mirror ICL circuit, a current mirror differential circuit at the second stage, and a SEPP circuit at the last stage. The allowable input of 300 mv is secured.
The head head amplifier section, a low-noise junction FET is adopted in the first stage, a constant-current drive circuit is used in the second stage, and a SEPP circuit is used in the last stage. This is a 3-stage direct connection structure.

The power supply section is equipped with a left / right independent power transformer and a large-capacity capacitor. In addition, a stabilizing power supply is used for the tone amplifier and head amplifier of the small signal system to prevent mutual interference between amplifiers.

Both speaker output jacks A and B use direct output jacks that connect directly to the speaker jacks without passing any signal through the speaker selector switch.

The power supply section and main amplifier section use a 70 μ s board that is twice as thick as the conventional one, reducing impedance from the power supply line to the output line.

Model Rating
Type Pre-main amplifier
Main Amplifier Section
Effective power 90W + 90W (8 Ω, both channel drive, 5 Hz to 40 kHz)
Total harmonic distortion factor 0.008% (5 Hz ~ 40 kHz, 8 Ω at Rated Output)
0.02% (8 Ω at 5 Hz to 100 kHz, 45W output)
0.002% (8 Ω at 1 kHz, rated output)
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1) 0.008% (8 Ω at rated output)
0.003% (8 Ω at 45W output)
Frequency characteristic DC ~ 100 kHz + 0 -1dB (DC)
Input Sensitivity / Impedance Main in : 1V/47k Ω
Signal-to-noise ratio (IHF, A-network) 115dB
Damping factor 80 (1 kHz, 8 Ω)
Load impedance 4 Ω ~ 16 Ω
Preamplifier Section
Input Sensitivity / Impedance Phono1, 2 mm : 2.5mV/100 Ω, 22k Ω, 47k Ω, 100k Ω /
100 pF, 200 pF, 300 pF, 400 pF
Phono1, 2 mc : 250 μ V/100 Ω
Tuner, Aux, Tape play1, 2 : 150mV/47k Ω
Output Level / Impedance Tape rec out1, 2 : 150mV/600 Ω
Pre out : 1V/600 Ω
Phono maximum allowable input
(1 kHz, 0.005%)
MM:300mV
MC:30mV
Total harmonic distortion rate (20 Hz to 20 kHz) Phono1, 2 mm, MC : not more than 0.005% (AT Rec out, 1 v)
Tuner, Aux, Tape play1, 2 : 0.005% or less (AT Pre out, 1 v)
Frequency characteristic Phono1, 2 : 20 Hz to 20 kHz ± 0.2 dB (RIAA deviation)
Tuner, Aux, Tape play1, 2 : 10 Hz to 100 kHz + 0 -2dB
Signal-to-noise ratio (IHF, A-network) Phono1, 2 MM : 90 dB
Phono1, 2 mc : 73 dB
Tuner, Aux, Tape play1, 2 : 100 dB
Tone control Bass : + / - 8 dB (100 Hz, turnover frequency : 50 Hz)
Treble : ± 8 dB (10 kHz, Turnover frequency : 20 kHz)
Low filter 15 Hz, 6dB/oct.
Muting -16dB
<Others>
Power supply voltage 100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law) 240W
AC outlet Power switch interlock : 2 systems
Power switch not linked : 1 system
External dimensions Width 435x Height 164.5x Depth 420 mm
Weight 20kg