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Adcom GFA-585 (1990–1997)

Fifty-one pounds, a 1.2 kVA toroidal transformer, and a price tag that undercut the high-end by two-thirds.

Overview

The GFA-585 launched in 1990 at $800. It was Adcom's flagship stereo power amplifier, sitting above the long-respected GFA-555, and it stayed in production through 1997. That's a long run for any amplifier and an especially long one for a flagship. Collectors call it a "giant killer," because buyers compared its clean, dynamic, effortless sound to amplifiers costing two to three times as much.

The design explains it. The GFA-585 is a fully complementary, direct-coupled, dual-mono amplifier built around a 1.2 kVA toroidal transformer, the kind of power supply iron that normally lives in a much more expensive chassis. Each channel uses five pairs of Sanken 2SC3264 / 2SA1295 output transistors. Cooling is entirely passive, through large heat sinks. There is no fan. That means the amplifier is silent in operation, but it also runs hot, and good ventilation is essential.

The rated output was specified as 200 watts per channel into 8 ohms (short-term RMS, both channels driven, 20 Hz-20 kHz). That figure is contested. A surviving service manual for the model rates the same amplifier at 250 watts into 8 ohms and 400 watts into 4 ohms, both at under 0.02% THD across 20 Hz-20 kHz. Whether the discrepancy reflects a mid-production revision, a different measurement standard, or Adcom's own loose paperwork is unresolved in the available record. Buyers should treat the 200-watt figure as the conservative one and the 250-watt figure as the one the service documentation carries. Dynamic power figures are more generous: 240W into 8 ohms, 360W into 4 ohms, and 300W dynamic in stereo (600W bridged mono) into 2 ohms. That low-impedance headroom is where the "giant killer" talk comes from.

The rest of the specification sheet reads like a serious amplifier. Frequency response runs from 5 Hz to 100 kHz (+0, -3 dB). THD is rated under 0.03% at rated power across 20 Hz-20 kHz, typically below 0.002% at 1 kHz. Signal-to-noise exceeds 110 dB (A-weighted), input sensitivity is 1.2V, damping factor is greater than 500 at 20 Hz, and gain is 26 dB. The chassis weighs 51 lb and measures 17 × 6.25 × 14.5 inches. None of these numbers is spectacular alone. Together they describe an amplifier built to be unflappable rather than flashy.

Key Features

Dual-Mono Topology with a 1.2 kVA Toroidal Transformer

Two channels, two power paths, one enormous toroid. The dual-mono layout keeps the left and right halves largely independent, and the 1.2 kVA transformer is the reserve that lets the output stage deliver current into low-impedance loads without sagging. Adcom's advertising leaned hard on this. A period ad in Audio (December 1990, p.92) emphasized the amplifier's "massive power supply" and its ability to deliver high current continuously, not just in short bursts.

Five Pairs of Sanken Output Transistors per Channel

Each channel runs five pairs of Sanken 2SC3264 / 2SA1295 devices in the output stage. That's a lot of silicon per channel, and it's why the amplifier can be rated for 300W dynamic into 2 ohms in stereo or 600W bridged mono. Owners report the GFA-585 stays composed into difficult loads in a way that smaller amplifiers in the line cannot. The trade-off is heat. With no fan and the output stage running in Class AB, the heat sinks do all the work, and the amplifier wants breathing room.

Balanced XLR and Unbalanced RCA Inputs, Switch-Selectable

The rear panel carries both balanced (XLR) and unbalanced (RCA) inputs, selectable via switches. That was not universal at the price in 1990. A mode switch offers stereo, mono (bridged), or A+B (biamp) operation, and there are two pairs of binding posts. For owners running a single amplifier in stereo, the second pair of posts makes bi-wiring straightforward. For owners running a pair bridged into mono, the mode switch unlocks the 600W dynamic figure into 2 ohms. An optional GR-4 volume controller added remote volume control via a motorized potentiometer. It shows up on the used market from time to time.

DC Offset Protection — and No Speaker Relay

One thing to know before buying: the GFA-585 has no speaker protection relay. It relies on DC offset protection only. In practice the amplifier is not going to disconnect your loudspeakers if something goes wrong in the output stage, because the protection circuitry monitors offset, not catastrophic failure. For owners pairing it with valuable speakers, that's a real consideration. It's also one of the reasons the model has a devoted following among technicians who know how to keep it healthy.

Historical Context

Adcom positioned the GFA-585 directly against designs from Krell and Threshold, at a fraction of their cost. That strategy defined the company's reputation in this era. The GFA-585 was the top of the line, sitting above the long-respected GFA-555, and it was eventually succeeded by the GFA-5802. Two limited variants were produced: the GFA-585SE (Special Edition), which added WBT binding posts, Cardas RCA jacks, and matched output transistors, and the GFA-585LE (Limited Edition), which featured a lower noise floor and upgraded capacitors. The standard model is by far the most common on the used market. The SE and LE variants are collector curiosities.

Collectibility & Value

The GFA-585 typically sells in the $400-$700 range on the used market, depending on condition and included accessories. That's a lot of amplifier for the money, but the model has known failure modes that buyers should price in. Mains hum from the large toroidal transformer is the most commonly reported complaint, sometimes addressable with a DC blocker, sometimes not. Channel imbalance traced to aging components on the voltage regulator board is another recurring issue. The foam blocks around the bias transistor on the heat sink also degrade with age, and that causes problems quietly until it doesn't.

Maintenance advice from the technician community centers on replacing the small-signal transistors (2SA970, 2SC2240) in the front end with modern low-noise parts for improved reliability. Full recap and upgrade kits for the model show up on eBay regularly. A complete recap/upgrade kit has been listed around $295, with partial upgrade kits around $135. Given the amplifier's age, a kit plus a competent technician's time is a realistic ownership cost, and it's the reason the $400 end of the market is often a better deal than the $700 end.

The GFA-585 runs hot. Good ventilation is essential, and buyers should inspect the heat sinks and surrounding components carefully before committing. The lack of a speaker protection relay is worth weighing against the value of the speakers it will drive.

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VINTAGE TECHNOLOGY ARCHIVE / 10-17-2026 / FEEDBACK