Boulder 500

Little is documented about the Boulder 500 power amplifier beyond its listing in period equipment directories and a few contemporary reviews. What the record shows is a substantial, high-current design from the early days of Boulder Amplifiers that quickly earned a reputation for build quality. The Sound-and-Communication (June 1986, p.47) review noted a 1,200 VA toroidal power transformer and four filter capacitors, with output via gold-plated five-way binding posts. A later HiFi/Stereo article (1988, p.66) listed the specs. Power was 125 continuous watts per channel from 20-20,000 Hz with less than 0.05% THD and IM distortion into 8 ohms. Dynamic headroom was 1.8 dB, slew rate 200 V/µs, damping factor greater than 175, and weight 351 lb. Dimensions were 17" wide × 6" high × 10" deep. The same source gave a U.S. retail price of $995, and mentioned a variant called the EA-230 - 30 W/ch with a conventional power supply. The 500 used soft clipping, negative feedback of 8 dB, and required 1 V for 170 W output. It was rack-mountable (19" faceplate). The 500 appears to overlap with Boulder's modular preamplifier concept introduced in 1988. The company offered the preamp in "small, medium or large" configurations depending on the user's needs, and the 500 power amp fit as a sturdy foundation for that system.

Surviving information on this model is thin. The magazine references are the best primary sources. The amplifier is respected among collectors for its overbuilt power supply and clean architecture. Specific circuit details, production run length, and serial-number ranges are not recorded in the sources examined.

Power output: 125 W/ch (20 Hz–20 kHz, <0.05% THD, 8 Ω)
Slew rate: 200 V/µs
Damping factor: >175
Dimensions: 17" w × 6" h × 10" d
Weight: 351 lb
Price at introduction: $995