Carver M-400A (1978)
Little is documented about the Carver M-400A under that exact name. The archive's catalog dates it to 1978, but the sources on hand don't include a manual or spec sheet that says what the "A" suffix meant. The period record does cover the Carver Magnetic Field Amplifier, usually listed simply as the M-400. At least one piece headlined "Pure Genius" in Audio (February 1983, p.21) calls the model the "M-400a" and cites 201 watts minimum continuous output. Nothing in the archive pins down whether "A" marked a running production change or was just inconsistent spelling.
The design got serious attention regardless of the suffix. Audio (November 1980, p.32) printed the manufacturer's specification of 201 watts per channel into 8 ohms from 20 Hz to 20 kHz at no more than 0.05% THD, with clipping at 250 watts per channel (1 kHz, 8 ohms) and 500 watts available from a single channel into 8 ohms. The output stage was unusual. HiFi-Stereo (October 1980, p.40) noted that the two channels were driven out of phase, one inverting and one non-inverting, so the "hot" side of one channel's black binding post was not at chassis-ground potential. That same out-of-phase connection made mono operation easy. Put the speaker across the two "hot" outputs, feed both inputs from a single signal, and the amp behaves as a high-power mono unit.
The bigger story was how Carver got that much power into such a small, light chassis. Bob Carver himself explained the Magnetic Field approach in Audio (June 1981, p.19). Conventional amplifiers of this output demanded large and expensive power transformers and electrolytic capacitors, while his design avoided that penalty. The archive's notes on the base M-400 record Carver's "Trackdown Downconverter" (actually "Tracking Downconverter") technology as the means, along with remarkably compact "cube" power supplies. The M-400A appears to belong to that same family.
Known specs from the period record:
- 201 W/ch into 8 ohms, 20 Hz–20 kHz, ≤0.05% THD (manufacturer spec as printed)
- Clipping: 250 W/ch into 8 ohms at 1 kHz; 500 W single-channel into 8 ohms at 1 kHz
- Channels driven out of phase; mono operation by bridging across the two "hot" outputs
- Compact "Magnetic Field" cube-style power supply
Production years, original price, and a service manual for the A variant aren't in the record. But the few facts above are the heart of the design — and for a model this thinly documented, that's the honest extent of it.
Market Value
┌──────────────────────────────────────────────────────────────────────────┐ │ CARVER M-400A Nov 2026 │ ├──────────────────────────────────────────────────────────────────────────┤ │ High $548 Latest $288 │ │ Median $373 Trend — │ │ Low $168 Volume ~3/mo │ ├──────────────────────────────────────────────────────────────────────────┤ │ $600 ┤ │ │ │ . │ │ │ . │ │ $386 ┤. . │ │ │ . │ │ │ .│ │ │ . │ │ $100 ┤ . │ │ ├─────────────────────────────────────────────────────────────────│ │ vol │█ █ █ █ █ █ █ █│ │ └─────────────────────────────────────────────────────────────────│ │ 2026-03 2026-05 2026-06│ └──────────────────────────────────────────────────────────────────────────┘
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