As part of the multisensory experimental box, there was a need for units of 7 speakers (1″ dome tweeters) which were to sit around the mouse to create virtual sound sources.
These were originally powered using small amplifier modules and a mess of wiring on stripboard; I decided to design a more robust, maintainable solution, which could easily be stacked to allow for more channels.
The existing amplifiers were wired up with RJ45 inputs and outputs; to maintain compatibility and avoid extensive rewiring I chose to use the same configuration. I designed a custom PCB for this, with fixed-gain amplification (set by a resistor network) on each channel, and custom low-pass filtering for the specific speakers used. The design incorporated soft-mute on start (to avoid pops / damaging the drivers), as well as thermal / overload protection thanks to TDA7375V quad amplifier ICs.
So far, over 10 have been built and are working reliably. The drivers are quite low-power and high-passed at 200Hz – as such the whole PCB runs in free air with no heatsink, but 35W/channel would be achievable with extra cooling if needed.
2017
