JBL SA640 (1980)
The JBL SA640 is a heavy stereo power amplifier from 1980, built by James B. Lansing Sound in Northridge, California. It was originally priced at ¥440,000 in Japan, where much of the surviving documentation originates. JBL developed it to drive their large-format studio monitors - the 4331, 4333, 4343, 4344, 4345, and nearly any other speaker in the lineup - and it holds low-impedance loads well.
Rated at 100W + 100W into 8Ω at 0.06% THD, the SA640 uses JBL's original T-type circuit. It's a symmetrical, pure complementary push-pull design with a 3-stage Darlington output. The summing point of the NF circuit is built from passive elements, which JBL said ensured stable operation and good linearity even with large inputs. The power supply uses a large EI transformer and a 40,000 µF capacitor bank, high-precision types originally developed for computers. Large heat sinks run along both sides. A temperature protection circuit doubles as a delay circuit to suppress shock noise at power-on. Nothing extra is added to the output path, with no additional circuitry in the signal path. The build uses precision metal-coated resistors and high-quality capacitors selected for sound quality.
The front panel has no tone controls or preamp functions. This is a straight power amplifier. Input sensitivity is 1.05Vrms into 8kΩ or more, signal-to-noise is 100dB (20Hz-20kHz, short circuit), and channel separation at 10kHz is 70dB. Output bandwidth runs from 0.16Hz to 200kHz (dynamic output) or 190kHz (electrostatic output). It draws 200W from a 100V AC line (50/60Hz), measures 432 × 140 × 342mm, and weighs 19kg. One owner on the audioheritage.org forums called it "very rugged and HEAVY!!"
That same owner described it as "a pretty well made amplifier," and a Russian listing praised it as "powerful, assertive, holds bass control excellently." One user on WhatsBestForum noted the ¥440,000 price seemed expensive for 1980, while another was curious about the sound quality. The sparse record doesn't answer that. The SA640 was also sold with the "T-Module" designation, and some sources hyphenate the name as SA-640. It's the same amplifier either way.
A used unit listed in Russia in April 2025 for 90,000 руб. and sold in June 2025 (marked "Sold on Avito"), with the seller noting small spots on the top panel and replaced acoustic terminals. Beyond that, the record is thin. No service manual or schematic has surfaced, no production end-date is known, and no original US dollar price has been confirmed.
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