Alesis RA-300
A 2×150W amp whose service manual has held up better than most of its owners' memories.
Overview
The Alesis RA-300 is a two-channel power amplifier rated at 2×150 watts. Alesis's own service documentation calls it a "professional amplifier." That service manual - the PE-QT-016-A parts and maintenance document, with a 2002 Alesis Distribution copyright - is the main reason the amp still has a paper trail, and it's a detailed one. The bill of materials breaks the RA-300 into board-level assemblies: a power indicator PCB, a power board, separate left- and right-channel driver boards, and separate left and right amp boards. Without the manual, a repair turns into guesswork.
The power supply is built around a 300W EI transformer with AC 115/230V input and dual 39.5V and 20V secondaries. It's a linear supply, not a switching brick. Mains protection is a 5×20mm fuse, specified as a GST6A250V for 115V operation and a 5TT3A250V for 230V. The amp was built to run on either mains standard, and the fuse value depends on which one it's set for. Buyers of used units should check that. A wrong fuse is one of the classic ways these end up on a repair bench.
Board-level detail is where the documentation gets generous. The amp boards run 2SC2240 and 2SA970 input transistors, 2SC1815GR and 2SA1015GR devices elsewhere, and BA4560 op-amps in DIP8 packages. The power board carries carbon film resistors at 1/8W, metal-oxide types at 1W and 2W, and metal film parts at 1%. The indicator board uses four LB1403N SIP9 ICs. That's the kind of part number that tells a technician whether the front-panel LEDs can be saved or the whole board is a write-off.
The LED and power sections share PCB designators with an "RA500" prefix. CB1017901000 is marked RA500LED V1.1, and the power board is RA500PWR V1.1. The amp boards carry RA300 designators (RA300AL, RA300AR). Some boards may interchange with other Alesis amps of the same generation, though the manual doesn't spell out which.
The manual also carries the standard Alesis warning that service work by unauthorized parties voids any remaining warranty, and that all repairs are performed at the owner's sole risk. That's boilerplate, but it fits the RA-300's situation today. You fix it yourself or hand it to someone who knows what a 2SA970 is. There's no factory support at the other end of a phone call.
Based on what's documented, the RA-300 is not audiophile exotica. It's a utility amplifier, the kind that sat in a rack powering studio monitors or a small PA. The 2×150W rating is honest for its class, the linear supply is heavier than it needs to be by modern standards, and the board-level serviceability is better than most of its contemporaries. The parts are mostly standard Japanese transistors and op-amps that are still findable.
That's the whole case for the RA-300: it's a documented, repairable, unglamorous amplifier that does exactly what the label says. In a hobby full of unobtainable exotica, that's not nothing.
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