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Hitachi HA-6800

Stereo Integrated Amplifier (1981)

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Hitachi HA-6800

Specifications

Power output: 70 watts per channel into 8Ω (stereo)

Frequency response: 1Hz to 200kHz

Total harmonic distortion: 0.008%

Damping factor: 60

Input sensitivity: 0.15mV (MC), 2.5mV (MM), 150mV (line)

Signal to noise ratio: 73dB (MC), 89dB (MM), 100dB (line)

Output: 150mV (line)

Dimensions: 435 x 145 x 392mm

Weight: 12.5kg

Year: 1981

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Reviews

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rating
Reviewed Nov 26th, 2017 by Prof-shadocko

Excellent ampli ! très dynamique, on reconnaît bien le son des lateral Mosfet, typé tubes avec la pêche en plus !

 

Comments

re: HA-6800

The Hitachi HA-6800 is a very clean and transparent sounding amplifier.

It is designed using a single pair of classical Hitachi lateral MOSFET power transistors per channel. The schematic shows the most advanced of the Hitachi amplifier designs, with an extra emitter follower stage before the second differential amplifying stage, plus an extra bipolar driver stage driving the MOSFET gates for better HF performance. When "main direct" is on, no capacitor is in the signal path, not even in the feedback loop, due to a DC servo.

Today, almost all HA-6800 suffer from aged components named "fuse resistors" which have either changed their value, both up or down, or are interrupted. Fuse resistors look like regular resistors but are marked in the schematic. Symptoms can be different, including oscillation. These resistors need to be replaced with either fusible resistors again or simply regular resistors. Fortunately, the MOSFET power transistors are very robust and almost never damaged, even after problems causing extreme heat.

A general renewal of electrolytic capacitors is advised, since the high temperature inside the device has accelerated aging effects.

Restoring the HA-6800 is worthwhile and relatively easy to do, knowing which are the critical components. Removing lid and bottom plate makes all components accessible.

This website is not affiliated with or sponsored by Hitachi. To purchase HA-6800 spares or accessories, please contact the company via their website or visit an authorised retailer.