Hitachi HA-3700

The HA-3700 was a stereo amplifier manufactured by the Hitachi Corporation of Japan in the early 1980s. It was one in a series of amplifiers consisting of HA-2700, HA-2800, HA-3700, HA-3800, HA-4700, and HA-4800. The HA-3700 was 35-watts per channel rms with an 8 Ω load, whilst the HA-4700 was 50-watts per channel. These amplifiers had the Super Linear Circuit feature, which was Hitachi’s solution for solving the problem of crossover distortion inherent in push-pull audio output circuits. The full specifications can be found in the user manual.

Review

In order to reduce crossover distortion, they included a four-transistor circuit in the bias network of the power output stage. These transistors ensure that neither of the final stage transistors fully switches OFF in the absence of an input signal. It works extremely well and the engineers call it super linear circuit.

One of the nice design features of this amplifier is the 80s style LED power meters that the engineers made an effort to construct using discrete components. This amp has 7 LEDs per channel to indicate the output power level. If you plan to connect a record player, then you will love the RIAA preamplifier based on the HA12017 integrated circuit (IC). This IC is ideally suited for this type of application and even has a SEPP output stage.

The audio power output stage consists of 2SD587 and 2SB617 complementary pair of silicon transistors with collector current rating (Ic) of 6 A. Amplifiers with these transistors usually stand out in terms of sound quality. Together with a Baxandall bass and tone circuit, it is capable of producing that lovely warm bass and sharp tone. In total, this marvel of Japanese electronic engineering has 3 ICs, 51 transistors, and 46 diodes of which 15 are LEDs. Its dimensions are 435 mm × 83 mm × 299 mm to fit into any standard stack system, and has a mass of 5.4 kg.

Price/eBay

The HA-3700 is an extremely desirable piece of Japanese electronic engineering and it is sometimes for sale on eBay. Usually, those who know and understand audio quality will buy it straight away because it has a wonderful sound quality found only in this amp. A burnt amplifier is very expensive and time consuming to repair and therefore not worth much. However, a good working amplifier in mint condition, together with the original manuals and box can easily go for over one hundred pounds and more.

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