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The Lo-D HCA 4580 is a control amplifier designed to achieve low noise and low distortion, a concept which, at the time, represented one of the strengths of Japanese manufacturing, which was focused on achieving the highest possible electrical precision. The equaliser circuit and tone control circuit utilised a differential constant-current drive in the first stage, and these circuits were designed to achieve low distortion and low noise through the use of a high-precision integrated circuit. Equipped with a dedicated microphone amplifier, it enabled microphone mixing even with the inclusion of the built-in analogue reverb. It also featured a switchable low-pass filter and a ‘Loudness’ selection to emphasise low frequencies when listening at moderate volumes. It featured two Tape inputs for cassette, reel-to-reel or MD/CD/SD recorders, two Line inputs labelled Aux and Tuner, and a Phono input for turntables, a configuration that reflected the great versatility typical of Lo-D/HITACHI equipment of the period.
The Lo-D HMA 3780 is a stereo power amplifier that utilised power MOSFETs, a cutting-edge technical solution for those years. The power MOSFET developed by Rodi was adopted as the output stage. The small-signal MOSFETs used in the front-end of FM tuners possessed excellent properties as power devices, but it proved difficult to achieve high breakdown voltage, high gain and high current characteristics. Rodi had focused on this MOSFET and conducted various basic research and experiments, eventually succeeding in developing a power MOSFET. The circuit configuration of the HMA-3780 was a constant-current Class A amplifier circuit driving a differential amplifier in the first stage and a pure complementary power MOSFET circuit in the second stage. It featured a simple 3-stage circuit configuration, including the power amplification stage. The capacitor was eliminated from the NFB circuit, and the DC amplifier configuration also eliminated the input capacitor. An external magnetic meter was adopted, capable of reading the peak output level directly from the power value.
By making full use of Rodi’s assembly technology, performance comparable to that of a dual-power amplifier was achieved, as it prevented the deterioration of the amplifier’s transient distortion factor caused by crosstalk between the left and right channels. The power output across the entire range was a substantial 50 W per channel into an 8-ohm load, a figure that placed this model among the most balanced and sought-after units in the series. The rear panel featured a switch to cut off low frequencies below 5 Hz, which could have damaged the speakers, and also allowed the connection of two pairs of speakers, designated A and B, selectable from the front panel.
The units on offer have been refurbished and are in full working order, with excellent cosmetic condition that further enhances their appeal to collectors.
