Power supplyThe β22 amplifier board does not include a power supply (PSU). It needs a separate dual-rail DC supply to provide power to the circuit.The recommended PSU to use is the σ22 tracking regulated PSU. Designed specifically to be β22's companion PSU, σ22 elegantly mirrors the all-discrete, fully-complementary, MOSFET-driven theme of the β22 amplifier, while offering low noise, high PSRR, wide bandwidth, well-behaved transient response, low output impedance, excellent line/load regulation and high output current capability. One σ22 PSU board is capable of driving up to four β22 boards when serving as a headphone amplifier. For speaker amp duty, one σ22 board should be used per β22 board. Other PSUs can be used, as long as it provides the required output voltage and current, and has enough performance not to compromise the quality of the β22 amplifier. The current draw from the β22 board is approximately 200mA per board as a headphone amplifier, depending on its quiescent current (bias) adjustment settings. As a speaker amplifier, the current draw could have peaks of over 5A per β22 board, while it idles at the same 200mA. It is a good idea to use a power supply with some headroom above the maximum draw. β22 is designed to operate between ±24V to ±30V DC rail voltages. Highest output voltage swing and output power is attained at ±30V, while ±24V will make the amplifier run cooler. The amplifier should not be operated outside the recommended supply voltage range. Do not use an unregulated power supply when β22 is configured as a headphone amplifier. The high ripple in an unregulated supply will compromise the performance. If β22 is being built as a speaker amplifier only, you may consider an unregulated supply if you're on a budget. The β22's high PSRR design helps minimize the performance loss, and any incremental noise due to rail ripple would be less audible because speakers are less efficient, and also due to the listening environment and distance. If an unregulated supply is used, do not allow the rail voltages to exceed ±30V give or take a couple of volts, or there is a risk of overvoltage damage. Always measure the actual output voltage of the power supply before connecting it to the amplifier for the first time, to make sure its output voltage is as expected. The recommended configuration for the β22 is to use an outboard power supply. This allows the power transformer and other AC components to be located far away from the sensitive amplification circuitry for minimum induced hum and noise. You may instead use a large chassis and put all β22 amplifier boards and the power supply in it, but be sure to position the power transformer and other AC components as far from the amplifier boards as possible. A toroidal power transformer is recommended in this setup for its lower magnetic field leakage. Main: β22 Main | Prev: Technical highlights | Next: Schematic diagram |
