JBL 2901 (1989–?)

The JBL 2901 is a professional power amplifier introduced in 1989, originally priced at $2,000. It was designed as a high-power studio monitor amplifier, and it also served as the power amp section of the JBL 2900 powered monitor system. Documentation is thin — most of what's known comes from a dated Studio Electronics product listing reposted on Gearspace and from a Sound On Sound review that encountered the 2901 while testing JBL 4400 series monitors. A 1993 issue of Mix Magazine listed JBL monitor models in a dealer showcase, including the JBL 4206, 4208, 4408A, and 4412A, with the 4408A priced at $650 (Mix Magazine, March 1993, p.113).

The amp delivers 250 watts per channel at 8 ohms, with a continuous sine wave output of 900 watts in bridge mode (engaged via a rear-panel switch). It's a Class AB design with a fully complementary, dual-mono, symmetrical circuit topology, said to be modeled after the JBL/UREI 6260. Frequency response is rated at ±0.1 dB from 20 Hz to 20 kHz, THD at less than 0.05 percent, and damping factor greater than 200 at 100 Hz. The power supply uses one massive toroidal transformer and four 22,000 µF filter capacitors, with six pairs of output transistors per channel. It weighs 34 pounds and sits in a 2U rack-mounting chassis.

What sets the 2901 apart from a typical studio amp is the built-in monitor controller on the front panel: power switch, level control, mute button, and a mono/stereo switch. Inputs are XLR and 1/4-inch combo jacks on the front, outputs are 5-way binding posts and Speakon connectors. There's also a built-in 85 Hz subwoofer crossover with balanced XLR outputs.

The amp uses a thermostatically-controlled, variable-speed fan for cooling, and includes DC offset, overcurrent, and thermal protection with status LEDs. Users on Gearspace praise its clean, transparent sound and ability to deliver high SPLs without audible distortion, noting precise imaging and flat frequency response. The fan is reportedly quite audible at high levels, though the amp runs cool even during extended sessions.

Known specs:

- 250W/ch at 8 ohms; 900W continuous in bridge mode

- ±0.1 dB, 20 Hz–20 kHz; <0.05% THD; damping factor >200 at 100 Hz

- XLR and 1/4-inch combo inputs; 5-way binding posts and Speakon outputs

- Built-in monitor controller with level, mute, and mono/stereo switches

- Built-in 85 Hz subwoofer crossover with balanced XLR outputs

- 2U rack chassis, 34 lbs

On the used market, the 2901 typically lists for $500–$900 on Reverb. Common issues: the fan can become noisy with age and replacement fans are hard to source, and capacitor replacement is recommended for units over 20 years old. Original JBL parts are increasingly scarce, and some units have been modified with different input transformers to reduce noise. The amp lacks a ground lift switch, which some users find limiting in studio setups. No production end date, dimensions, or signal-to-noise specs are documented.