Cerwin-Vega A-400 (ca. 1979)
A rack-width, fan-cooled amplifier that Cerwin-Vega built to live in the same rack as the studio gear. The service manual reads like it expects you to fix it yourself.
Overview
What the A-400 is shows up in the service documentation, not the spec sheet. Cerwin-Vega opens its own manual by warning that these are professional, high-power amplifiers that "absolutely require proper test equipment and qualified service personnel," then lists what you'll need: a digital multimeter or VTVM, a dual-trace oscilloscope, an AC current meter, a 20-amp variac, a distortion analyzer with residual distortion of .002% or better, and load resistors rated for a kilowatt at 2 and 4 ohms. That is not the tool list for a receiver. It's the list for something that can hurt you and your bench.
The manufacturer's specification table backs that up. The A-400 is rated at a minimum continuous 225 watts per channel into 8 ohms, 20 Hz - 20 kHz, both channels driven, and 350 watts per channel into 4 ohms under the same conditions. Note the word "minimum." Cerwin-Vega wasn't quoting a peak, a one-channel number, or a 1 kHz burst. This is the floor, full bandwidth, both channels loaded. Period coverage worked from a slightly different figure: Modern Recording (August 1979, p.73) described the A-400 as rated to deliver better than 200 watts per channel into 8-ohm loads, or over 350 watts per channel into 4-ohm loads. Either way, the amp was built on the assumption that the speakers hanging off it are inefficient and the room is large.
The distortion numbers surprise people who file Cerwin-Vega under "loud." Total harmonic distortion across 20 Hz - 20 kHz, from a quarter-watt up to full power, is specified at 0.03% into 8 ohms and 0.05% into 4 ohms. SMPTE intermodulation distortion over the same quarter-watt-to-full-power range at 8 ohms is also 0.03%. Signal-to-noise referenced to rated output with A-weighting is 113 dB, an extraordinary figure for the period. IHF noise, referenced to 0 dBW with A-weighting, is −90 dB.
Power bandwidth is specified as 7 Hz to 100 kHz. Slew rate is 80 volts per microsecond. Damping factor, referenced to 50 Hz into 8 ohms, is 250. Input impedance is 10 kΩ, input sensitivity for full output is 1.4 V, and IHF sensitivity referenced to 0 dBW is 0.094 V. So it takes a normal line-level signal and turns it into a great deal of power without asking much of the source. Inputs are phono (RCA) or ¼″ phone jacks, and the phone jack is the tell that this amp was expected to sit in a studio rack as readily as on a home shelf. Output connections are dual five-way binding posts.
Physically, it's a rack piece. Mix Magazine (May 1979, p.45) listed it at 19 × 5.25 × 13 inches and 31 lbs. The 19-inch width and 5.25-inch height are standard rack dimensions, and the front panel, per Modern Recording (August 1979, p.73), is plain: handles and a power switch, nothing else. Cooling is by fan, which is the price of this much output in a two-rack-space chassis. Expect to hear it running.
Key Features
225 Watts Minimum, Both Channels, Full Bandwidth
The headline number is the minimum continuous rating: 225 W per channel into 8 ohms and 350 W per channel into 4 ohms, both channels driven, 20 Hz - 20 kHz. That phrasing is the honest way to rate an amplifier, and it's the number to trust over any peak or burst figure. The 4-ohm rating matters more than the 8-ohm one for the speakers this amp was sold to drive. The jump from 225 to 350 W per channel as the load halves points to a power supply with real reserves rather than a stiff regulator that folds under low impedance.
0.03% THD and 113 dB Signal-to-Noise
THD is specified at 0.03% into 8 ohms and 0.05% into 4 ohms, measured from a quarter-watt all the way to full output across 20 Hz - 20 kHz, not at a single frequency. SMPTE IM distortion at 8 ohms is also 0.03% over the same range. The 113 dB A-weighted signal-to-noise figure is the standout. It puts the amplifier's own noise floor far below anything you'd hear from the source or the room.
7 Hz–100 kHz Power Bandwidth, 80 V/µs Slew Rate
The power bandwidth extends from 7 Hz to 100 kHz, and the slew rate is 80 V/µs. Together those describe an amplifier that isn't going to round off transients or choke on ultrasonic content. Damping factor of 250 at 50 Hz into 8 ohms keeps the bass controlled on speakers whose own impedance swings would otherwise let the amp wander.
RCA or ¼″ Phone Inputs, Five-Way Binding Posts
Inputs are phono (RCA) or ¼″ phone jacks, and that dual provision is what let the A-400 straddle the pro and home markets. Output is via dual five-way binding posts, so bare wire, spades, bananas, or pins all work. Input impedance is 10 kΩ, full output arrives at 1.4 V input, and IHF sensitivity at 0 dBW is 0.094 V. It takes a normal line-level signal and makes a great deal of power without needing a hot source.
Fan Cooling and a Protection Circuit That Actually Protects
The A-400 is fan-cooled, and the protection circuitry is more elaborate than the front panel suggests. The manual describes three sense mechanisms. Excessive current or oscillation across the output emitter resistors triggers a discrete logic gate that fires a 555 timer. Sustained DC offset at the output is summed and integrated and triggers the same timer. Loss of AC power or low line voltage is caught before it can send a transient to the speakers. When the timer fires, it holds for roughly seven seconds, lights the protect LED, and de-energizes the output and input relays, disconnecting the amplifier from everything downstream. Peak-clip indicators sit after the output relay, so they stay dark while the amp is in protect.
A Service Manual That Assumes You'll Use It
The service documentation runs 47 pages and reads like it was written for a working bench tech, not a warranty depot. It walks through bias and DC-offset adjustment (bias set to 22-28 mV, offset nulled to within about 10 mV of zero), a step-by-step protection-fault flowchart, and output-stage troubleshooting down to checking the 0.47 Ω emitter resistors for current indicating a bad output device. The output stage uses paralleled devices Q601 through Q608, with a bias-compensation transistor (Q301) mounted against the heat sink to track temperature.
Historical Context
The A-400 belongs to Cerwin-Vega's late-1970s push toward the studio and serious-listener market, and the period press noticed the blurring. Modern Recording (August 1979, p.75) observed that the dividing line between "professional" and home-audiophile amplifiers was growing fuzzy, and placed the A-400's measured performance - IM and harmonic distortion, TIM, slew rate, transient response - in the top class of either category.
Within the Cerwin-Vega lineup, the A-400 is documented alongside the A-600 as a related solid-state model, and it appears in listings of the company's power amplifiers next to the CV-900. Owner accounts describe it being used in pairs with the A-600 in DJ rigs, the A-400 handling vocals and the larger amp on the low end. Production dates beyond the 1979 reviews haven't surfaced; "ca. 1979" is as precise as the record gets.
Collectibility & Value
These aren't yet commanding collector prices, but they're not being given away either. The Audiogon blue book lists an original retail of $900.00, and a Spanish-language listing surfaced at €800 in May 2023 - an asking price, not a confirmed sale. A Reverb restoration kit (filter capacitors and rebuild parts) sold for $185 in August 2022. eBay examples have shown up "powers on but needs work," sold for parts or restoration, so buy accordingly. A tested, working unit is worth substantially more than a project.
The known trouble spot is the protection board. A YouTube teardown titled "Cerwin Vega a-400 with hidden issues on protected PCB" is the only documentation of it, and there's no detail beyond the title, but it's consistent with the manual's emphasis on the protect circuit. The bias and offset adjustments are preset at the factory and shouldn't drift, but any unit that's had output transistors replaced will need them checked. With a 47-page service manual and rebuild kits available, the A-400 is a maintainable amplifier.
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