BOULDER 500

Pre owned. In fair condition. Shows signs of wear on the edges as visible in the photos. Original packaging not included.

The Boulder 500 amplifier originates from Colorado and, after extended use, establishes itself as a top-tier device, clearly standing out within its category. Designed by Jeff Nelson and Randy Gill of Silver Lake Research, it marks the transition from the professional market to the audiophile sector, while maintaining a strongly technical approach tailored to the needs of recording studios. Its design and features clearly reflect this heritage: balanced and unbalanced inputs, conductive plastic level controls, and a comprehensive protection system all highlight its professional orientation. The build quality conveys solidity and precision, with a robust chassis and an exceptionally rich internal component layout distributed across multiple circuit boards. Inside, it houses a powerful 1200VA toroidal transformer, large-capacity filter capacitors, and numerous high-performance output transistors designed to handle substantial power with absolute reliability.

At the core of the amplifier lies the discrete 990 operational amplifier developed by Deane Jensen, here adapted for high-voltage and high-current operation. Unlike conventional integrated circuits, this solution ensures greater stability, lower distortion and noise, as well as superior slew rate and bandwidth. The design employs two cascaded gain stages, enabling high dynamic performance and efficient power handling. A significant amount of negative feedback is carefully optimized to avoid typical transient intermodulation distortion issues, thanks to precise gain parameter selection and compensation for delays in the feedback loop. The result is impeccable behavior even with complex signals, as demonstrated by the extremely accurate and well-controlled square-wave response, free from unwanted oscillations.

The fully DC-coupled configuration extends frequency response down to extremely low values, improving low-frequency reproduction and transient accuracy. A servo system manages any DC offset, ensuring speaker safety and automatically intervening in case of anomalies. The amplifier also incorporates advanced protection systems against short circuits and overheating, continuously monitoring component temperatures and acting to preserve operational integrity.

In listening tests, the Boulder 500 immediately stands out for its exceptional transparency and clarity, delivering a remarkably clean musical reproduction with significantly reduced noise and electronic artifacts. The silence between notes is particularly noticeable, contributing to a more realistic and engaging presentation. After a short warm-up period, performance stabilizes, revealing a neutral tonal balance and a remarkable ability to faithfully reproduce the character of upstream equipment. Its high resolution brings out every detail in the recording without masking imperfections.

The high frequencies extend with precision and control, maintaining a slightly analytical character without ever becoming overly bright, while the midrange remains clean, well-focused, and highly detailed. The soundstage offers good depth and width, though without the holographic imaging typical of some tube electronics. The overall presentation remains consistent with solid-state philosophy, featuring a slightly more incisive texture compared to the softness of tube gear, yet always balanced and comfortable even during long listening sessions.

Its most evident strength lies in low-frequency reproduction, where the amplifier demonstrates exceptional control and precision. Transients are handled effortlessly even under demanding conditions, ensuring outstanding pitch definition and a sense of authority and solidity that gives the bass range a concrete and well-articulated presence.

Technical specifications:

• Solid-state stereo amplifier
• Maximum continuous output power: 150 W into 8 ohms (21.75 dBW); 250 W into 4 ohms (21 dBW)
• Bandwidth: 100 kHz
• Voltage gain: 26 dB
• Signal-to-noise ratio (unweighted): 115 dB
• Peak current (10 ms): >50 A
• Input impedance: 10 kΩ balanced; 20 kΩ unbalanced
• Dimensions: 43.8 cm (W) x 63.5 cm (D) x 17.8 cm (H)
• Weight: 23.1 kg