Electro-Voice AP3200
A rack-mount amp that delivers 400 watts per channel into 8 ohms and shrugs off shorted loads, RF interference, and the kind of abuse that kills lesser amps.
Overview
The AP3200 is a two-channel power amplifier built for professional sound reinforcement. It weighs 52 pounds net, with a 16-gauge steel chassis and a 3/16-inch 5052 aluminum front panel. It's made to live in a rack and stay there. The level controls are on the rear panel, so you set them during installation and forget them. Nobody bumps a gain knob mid-show.
The numbers are serious. Each channel delivers 400 watts continuous into 8 ohms at less than 0.05% THD, or 600 watts into 4 ohms at less than 0.10% THD, across the full 20 Hz-20 kHz range. Bridge the two channels and you get 1200 watts into 8 ohms. Those are continuous ratings, not peak. Maximum midband output at 1% THD is higher: 450 watts per channel into 8 ohms, 725 into 4, and 1450 watts bridged into 8. Sound and Communication (February 1991, p.68) covered the amplifier's introduction and noted the 600-watt-per-channel-into-4-ohms figure as the headline spec, which lines up with the manual's continuous ratings.
For subwoofer duty, Electro-Voice rates the AP3200 at 420 watts per channel into 8 ohms or 650 into 4, measured from 20 Hz to 1 kHz at under 0.1% THD. Bridged, that's 840 watts into 16 ohms or 1300 into 8.
The protection circuitry sets the AP3200 apart from a lot of high-power amplifiers of its era. Each channel is independently guarded against excessive output voltage, shorted loads, excessive phase shift, RF interference, and over-temperature conditions. The load itself is protected from startup and shutdown transients, DC faults, infrasonic signals, and low AC line voltage. When something goes wrong, an output relay disconnects the speaker from the channel and lights the Protect LED on the front panel. That relay-based approach is a big part of why these amps developed a reputation for surviving real-world abuse in touring and install work.
The input stage is electronically balanced, with per-channel impedance above 30 kilohms balanced and above 15 kilohms unbalanced. Maximum input level is +20 dBu (7.75 V rms), and input sensitivity for rated output is +0.2 dBu (0.79 V rms) into 4 ohms dual mode or 8 ohms bridged. Voltage gain is 36 dB in dual mode and 42 dB in bridge mode. Channel separation exceeds 80 dB at 1 kHz, and noise is better than 100 dB below rated output, A-weighted. Slew rate exceeds 30 V/µsec in dual mode and 60 V/µsec bridged. Damping factor into 8 ohms is greater than 250 from 20 Hz to 1 kHz, dropping to greater than 75 at 20 kHz. That means tight, controlled bass with speakers that present difficult loads.
Frequency response runs from 10 Hz to 90 kHz at +0/-3 dB, and power bandwidth is a full 20 Hz-20 kHz at +0/-1 dB. THD is under 0.10% at rated output in any mode, SMPTE intermodulation distortion is under 0.05%, and TIM (DIN 100) is under 0.05%. Rise time is under 6 microseconds. Dynamic headroom is at least 0.25 dB in any mode. These aren't spectacular numbers by modern Class D standards, but they're honest ones.
The pair of octal accessory sockets on the back panel is one of the more interesting features. They accept plug-in modules: the APM-1 bridging input transformer, low-pass filter modules at 125, 500, 800, and 1250 Hz, high-pass modules at the same frequencies plus 315 Hz, and crossover modules including the APX and APX-2 two-way 24 dB/octave Linkwitz-Riley designs and the CX-1, which adds switch-selectable high-frequency attenuation, 500 or 800 Hz crossover points, and provisions for horn EQ and low-frequency delay. There are also five output impedance matching devices available: TR150, TR300, and TR600 70-volt line transformers, plus AT300 and AT100 multi-tap autoformers. The accessory sockets draw no more than 25 mA DC each, and the amp ships with four "U" jumper plugs installed - two per socket - for use when no modules are fitted. This was unusual for a power amp of this class and made the AP3200 adaptable to distributed sound systems, constant-voltage installations, and biamped configurations without external processing.
The power transformer is a standard multi-voltage type, permitting operation at 120 or 240 V AC, 50/60 Hz. A 100-volt, 50/60-Hz model was also available. Cooling is handled by a two-speed fan. The output topology is true complementary symmetry. The amp is rated for ambient temperatures up to 60°C (140°F), which suits cramped racks and hot equipment rooms.
The AP3200 takes up 5.25 inches of rack height - three rack units - and is 15.75 inches deep. Shipping weight is 62 pounds; net weight is 52 pounds. The chassis is black. The front panel is 3/16-inch 5052 aluminum alloy, thick enough to resist bending and rack rash. The AC fuse is a Littelfuse 3AB, 15-amp, 1250-volt SLO-BLO ceramic cartridge or equivalent.
Mix (March 1991, p.130) reported on the AP3200 as the most powerful amplifier in Electro-Voice's pro sound contracting line at the time of its introduction, positioning it above the company's other offerings in the category. That context matters for collectors and installers trying to understand where this amp sat in the lineup — it was the flagship, not a mid-tier option.
The manual includes a power-loss table for 2-wire speaker cable that runs from 6 AWG down to 22 AWG, with DCR per foot and power loss per foot listed for each gauge. Cable gauge matters when you're pushing 600 watts down a long run.
Electro-Voice offered a limited warranty on the AP3200: two years from the original purchase date against defects in workmanship and materials, with repair or replacement at the company's option. The warranty explicitly excluded finish and appearance items, damage from abuse or operation outside specified conditions, and incidental or consequential damages. Repairs by anyone other than Electro-Voice or its authorized service agencies voided the guarantee. Service was available through Electro-Voice facilities in Buchanan, Michigan; Visalia, California; and Oklahoma City, Oklahoma.
For anyone considering one of these today, the AP3200 represents a specific kind of value: a heavy, overbuilt, modular power amplifier from an era when Electro-Voice was a serious player in professional sound reinforcement. It's not a hi-fi amp, and it was never meant to be. It's a workhorse designed to run at high power levels for extended periods, and the protection circuitry means it can take a lot of punishment. The accessory sockets, if you can find the modules, add flexibility that most modern amplifiers simply don't offer. The main concerns are the usual ones for gear of this vintage: capacitor aging, fan bearing noise, and the general unavailability of some of the optional plug-in modules. But the core amplifier — 52 pounds of steel, aluminum, and complementary-symmetry output devices — is about as straightforward as professional power amplification gets.
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