Carver PM-350 (1986–1990)
A 21-pound pro amplifier that delivers 350 watts per channel and 900 watts bridged. The magnetic-field design cut weight, heat, and cost per watt.
Overview
Twenty-one pounds. That's what a 350-watt-per-channel professional power amplifier weighed when Carver released the PM-350 in July of 1986. For anyone who had hauled iron-heavy amps into studios and onto stages, that number was the whole story. The PM-350 was a stereo power amplifier rated at 350W per channel into 8 ohms and 450W per channel into 4 ohms. In bridged mono mode it delivers 900W into 8 ohms. It also handled 1000 watts into a 70V distribution system, which mattered to the permanent-installation crowd, where long speaker runs and distributed systems are the norm.
The secret was Carver's magnetic-field amplifier design, built around a triac phase-controlled power supply and multiple-level DC amplifier supplies. The manual is blunt about the payoff: the design "greatly reduces size, weight, heat and cost per watt." This is a real engineering departure from the conventional linear supply approach, and it's why the PM-350 could sit in a rack where other amps of comparable output would have needed a road case and two people to move. The 350W into 8 ohms figure was specified from 20 Hz to 20 kHz with no more than 0.5% THD, both channels driven. That's a full-bandwidth rating, not a 1 kHz shortcut.
Carver positioned the PM-350 for permanent installation, studio, and concert use. The company's own advertising in Sound & Communication (December 1986, p.15) framed it as part of a family that started with the professionally successful PM-1.5. The ad copy noted that the PM-350 could accept a range of accessory modules, including a programmable 2-way stereo crossover with 24 dB per octave Linkwitz-Reilly phase-aligned circuitry, a built-in adjustable high-end limiter, and balanced outputs. The modular approach was built into the rear panel, where an accessory cover could be removed to install the Carver PMX Electronic Crossover Module, the PG/2 Paging Module, or the PMT-2 Input Module for transformer-balanced inputs. The Mix (June 1987, p.133) advertisement made the same point: this amp was meant to be configured for the job at hand.
The PM-350 asks a little more attention from its owner than the average amp. The input section was electronically balanced and could be driven from either XLR or parallel TRS 1/4" phone jacks. There's a serial-number wrinkle here that matters to anyone buying used. From S/N 0001 through 1625, the XLR inputs were wired pin 2 high, following the DIN standard. Beginning with S/N 1626, Carver switched to pin 3 high, the American standard. If a PM-350 is mated to a console or processor and something sounds out of phase, that's the first place to look. The PMX crossover interconnect also changed at S/N 5001, and PMX units below S/N 600 won't plug into later amplifiers without modification or an adapter.
The protection and monitoring circuitry was unusually comprehensive for the era. Four LEDs on the front panel covered Power On, Protect, Clip, and Signal Present. The Signal Present LED lights at about 0.1 watt output into 8 ohms in dual-channel operation, or 0.5 watts in bridged mono. That's sensitive enough to confirm signal flow before any real level is applied. The Protect LED had two distinct behaviors. A bright LED lasting four seconds indicated an external problem like a short circuit or excessive high frequency, while a dim LED pointed to an internal amplifier or power supply fault. That kind of diagnostic differentiation was rare in 1986.
Cooling was handled by a variable-speed fan that increased airflow in direct proportion to power output, controlled by the triac conduction angle. When the heatsink reached about 50°C, a thermal switch closed and shorted out a resistor, roughly doubling the airflow. The amp runs quiet at idle and cools hard when it's working, which suits studio racks where fan noise is unwelcome.
Specifications: frequency response was 20 Hz to 20 kHz (+0, -0.5 dB). Damping factor exceeded 200 at 1 kHz. Input impedance was 15k ohms unbalanced or 30k ohms balanced. Sensitivity was 1.5V rms for rated power into 8 ohms at 1 kHz, or 80mV rms for 1 watt output into 8 ohms at 1 kHz. Gain was 31 dB. Input overload was +15dBu. IM distortion was less than 0.1%, and THD was less than 0.5%. Noise was -115dB A-weighted referenced to rated power, or -89dBW A-weighted referenced to 1 watt. Slew rate was 25V/µS. Power consumption at full power was 1200W. The unit measured 3.5" x 19" x 11.5" (13.5" overall depth) and weighed 21 lbs. - 9.5 kg. It ran on 120VAC/60Hz in the USA and Canada, or 230VAC/50Hz in Europe.
Service documentation for the PM-350 is thorough. The manual includes a full test procedure with specific voltage checks: ±75Vdc on the large filter capacitors, ±43Vdc on the cathode of D19 and anode of D21, ±21Vdc on the cathode of D15 and anode of D17, ±13Vdc on U2 pins 4 and 8, and ±10Vdc on U101 pins 4 and 8. Idle current is set by adjusting RP-100 and RP-200 for 2.5mVdc (±0.5mV) across R133 and R233 respectively, after a two-minute warm-up. The manual also warns that all primary waveforms must be viewed with an isolated, line-triggered scope with no secondary ground reference. The 115V version is fused with an MDQ 10 amp fuse; the 230V version uses an MDL 6-1/4 amp fuse. Both are thermally protected by a 100°C thermal breaker.
Production ran from July 1986 until early 1990, when Carver redesigned and renamed the entire professional power amplifier line for the 1990s. The PM-175, announced alongside the PM-350 in the same advertising campaign, extended the concept downward, but the PM-350 was the flagship of that initial pro push.
The PM-350 is still a usable amplifier, with enough clean power to drive just about anything. Its light weight makes it practical in a way that most 350W-per-channel amps aren't. The modular rear panel means it can still be configured for a specific task if the modules can be found. The comprehensive protection circuitry means it's less likely to have been abused than some of its contemporaries. And the service documentation is good enough that a competent tech can keep one running.
The caveats are the usual ones for vintage pro gear. The serial-number variations in XLR pinout and PMX interconnect mean compatibility has to be checked before mating a PM-350 with other Carver modules. The fan, while variable-speed and quiet at idle, is a mechanical part that will eventually need attention. The magnetic-field power supply is efficient but not a conventional design, so a tech who doesn't understand triac phase control should read the manual carefully before diving in. The manual itself warns that attempting repair without understanding the circuit description "may lead to severe damage to the unit."
What the PM-350 represents, ultimately, is a moment when Carver took a genuinely unconventional approach and made it work in the professional world. The Mix (February 1987, p.39) advertisement noted that the PM-1.5 had already proven itself professionally, and that the PM-175 and PM-350 were the next step in that family. For anyone who appreciates engineering that prioritizes efficiency and practicality over convention, the PM-350 is a compelling piece — not because it's rare or glamorous, but because it solved a real problem in a way that few other amplifiers of its era did.
Similar items on eBay
No exact Carver PM-350 listings are live right now — these searches show current Carver and similar vintage audio gear on eBay:
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.