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60W RMS per channel at 1% THD

We’ve measured the output power of the PiFi-240 amplifier, and it’s capable of a sustained 60W RMS per channel into 4 ohms at <1%THD.  It won’t do this indefinitely without additional heatsinking – the amplifier chips are generating about 6W of heat each at this level of output and the PCB is effectively a 20-25 °C/W heatsink as it stands, which is insufficient to keep the amplifier temperature under the 150°C at which the thermal cutout operates. But it will deliver this amount of power for several seconds (we’ll know more once we’ve taken some detailed thermal measurements) which is way longer than required for music transients.

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Driver code available

The driver for the PiFi-240 amplifier’s now available in the Raspian source tree – many thanks to Phil Elwell for patiently walking us through the process.

We’ve also been taking some measurements just to verify its performance, and it’s where it should be according to the datasheets – THD+N is <0.05% at 1W across the board.  Next up is to measure its thermal performance – how its temperature in still air changes with average power output – and to verify the peak power output available.

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Introduction

Welcome to PiFi Ltd. We’re building a range of audio hardware for Raspberry Pis (and other similar SBCs) and we’re about to release our first product to manufacturing.

It’s a HAT which implements a stereo 40W per channel Class D amplifier. There’s a number of differences between it and similar products on the market:

  • It uses a pair of amplifier chips, one for each channel. Each of those amplifiers is a stereo amp, and we pair its two channels together to give better audio quality, reduce losses and increase the available power output.
  • It’s stackable.  So, if you want to bi-amp your speakers, stack two of them.
  • It contains an on-board fan control output which can drive a 5V fan at variable speeds.

It runs from between 12 and 24V DC and contains an onboard power supply so that it can power its host Raspberry Pi.  It’s capable of peak speaker output currents in excess of 8A, and has oversized output filter inductors to cope.  Lastly, it’s built on a 4-layer PCB, which, importantly, improves heat conductivity away from the amplifier chips to allow them to provide higher output for longer periods as well as allowing us to have an unbroken ground plane.

We expect to be shipping by the middle of November.

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