Boulder 500-AE (late 1990s)
The Boulder 500-AE is an integrated amplifier built for the company's 25th anniversary. It is a more practical, all-in-one version of the 500-series separates. It originally sold for US$4,995 (¥650,000 in Japan), and was meant to deliver "statement" level performance without the separate-chassis complexity of Boulder's top-end gear.
The design is distinctive: fully complementary, dual-differential, direct-coupled, single-stage, with no overall feedback. The amplifier runs in class-A up to its first watt. A front-panel bias control has four settings - High, Medium, Low, and Off - so the user can shift between cleaner, cooler operation and a warmer, more saturated sound. The power supply uses a toroidal transformer, four 15,000µF filter capacitors, two 1,000µF output capacitors per channel, and a separate supply for the input stage. The output stage has four pairs of output transistors per channel. Construction is heavy-duty: four-layer circuit boards with plated-through holes, gold-plated input jacks, Teflon-insulated wiring, and military-spec components.
The 500-AE delivers 120 watts per channel into 8 ohms, doubling to 240 watts into 4 ohms. Frequency response runs from 0.1Hz to 200kHz (-3dB), and from 20Hz to 20kHz within ±0.05dB. Input impedance is 47 kilohms, gain is 26dB, and damping factor is rated greater than 200 (typically 600). Distortion is specified at less than 0.02% THD. A ¼" headphone jack is on the front panel. The chassis measures 19" wide, 5.25" high, and 13.5" deep, and weighs 45 pounds.
Audio (February 1990, p.72) tested the 500-AE and noted that they couldn’t recall testing an amp with distortion as low as the 500-AE exhibited — a striking compliment for a zero-feedback design. The review data showed extremely low distortion figures.
The bias control is the 500-AE's most talked-about feature. In the "High" setting, the amp runs hot on purpose and generates a lot of heat. The "Off" setting silences the amplifier entirely, so it works as a standby. Period reviews praised its "sense of effortlessness" and "explosive" dynamics, and one reviewer noted that bass control is superb. As of the early 2020s, used units have held reasonably steady around US$3,000-$4,000. Some internal parts, including the Motorola output transistors, are now obsolete, so servicing can be a challenge.
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