A250W class AB amplifier review

This test review was performed to comply with FTC: 16 CFR Part 432 (July 5, 2024) - Power Output Claims for Amplifiers Utilized in Home Entertainment Products

A250W is a big DIY class AB amplifier with rated power 2 x 250W/4ohm/1kHz/THD+N<1% and 2 x 150W/8ohm.

1. Test conditions

The amplifier was tested with both channels running, each loaded with a 4ohm resistor load. I have one 4ohm/400W and one 4ohm/200W resistor loads, both mounted on heatsinks.

2. Pre-conditioning

First of all, the amplifier was pre-conditioned for one hour at 1/8 of the rated power in both channels, i.e. at 2 x 31.25W/4ohm. At the end of the pre-conditioning period, the amplifier was hot, with hotest places of the heatsinks at 58°C. There was almost no change in distortion during the test. It started with THD = 0.0025% and finished with THD = 0.0028%.

3. Power frequency response and distortion

Frequency response was measured at 241W output power into 4ohm, from 10Hz to 40kHz with measuring BW45kHz.

Power frequency response covers whole audioband at 241W/4ohm with THD << 1%

4. Distortion

4.1.1 THD vs. level at 1kHz/4ohm stepped sine method 0.8s burst 0.5s interval with measuring BW90kHz

The amplifier distortion is below 1% at 250W/4ohm

4.1.2 THD+N vs. power at 20Hz and 1kHz/8ohm

4.2. THD vs. frequency at 241W/4ohm with measurement bandwidth 45kHz

4.2.2 THD vs. frequency at 125W/8ohm with measurement bandwidth 90kHz

4.3. CCIF IMD 19+20kHz at 60W/8ohm with measurement bandwidth 45kHz

4.4. 5 minute sine test

The amplifier has passed 5 minute test at 2 x 250W/4ohm/1kHz with THD = 0.68% and THD+N = 0.69%, being hot at the end of the test period, but colder than during pre/conditioning. The 4ohm/200W resistor load was, however, very very hot, at 120°C.

Pavel Macura 12/2/2024