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Power supply
The TA2022 chip in AMP5 requires a dual rail power supply plus a stabilized +5V 100 mA supply. The rail voltages could be +/-20V to +/-35V. Higher voltage gives a higher possible maximum power output. The limitations are about +/-35V upper limit voltage and the chip has an internal current limiting set at about 7.5A. With 4 ohm speakers or 8 ohm bridged mono, +/- 31V is the maximum recommended by Tripath, to avoid tripping the over-current shutdown at high power. With 8 ohm loads, +/- 35V can be used without tripping the over-current limit. Toroid transformers are available with standard values. Nominal voltages of +/-18VAC to +/-24VAC are common. When rectified, this will give about +/-24VDC to +/-33VDC. Note that transformer voltages are given for full rated power. At low power, the voltage will be slightly higher. For maximum power into 4 ohms, a 2x22VAC transformer would be about ideal, while for 8 ohms, 2X24V would be about the maximum.
The VA (power) rating depends on the voltage rating and the load impedance. At the upper end, with a +/-24VAC transformer (which is slightly high as seen above) and 4 ohms speaker load or a 8 ohm bridged load, a VA rating of 300 VA(≈300Watt), or even more, is reasonable, while a with +/-18VAC transformer and 8 ohm loads, as low as 80 VA may be sufficient.
Generally, the higher transformer VA rating, the better, as it is more stable, “stiffer”, and runs cooler. The only drawbacks are price, size and weight. But there may not be mush advantage going to very high VA values.
Bulk capacitors of 10.0000 uF per side are included with the kit. There is space for two 10.000 uF capacitors per side on the PCB, and this is useful for very high power applications. A kit with two more 10.000 uF capacitors and an extra rectifier is available from 41Hz Audio.
The power ground of the PCB is normally grounded into one point with the mains ground (earth) and to the housing ground.
The +5V is used for the analogue input amplifier and the in-chip digital parts of the TA2022. It needs to be well stabilized and well bypassed. On the board there is a regulated supply for the +5V. It uses a LM317 voltage regulator and taps from the positive main supply. The +5V should not draw more than about 60 mA. A jumper J10, can break the +5V supply which can be useful when testing.
