BS2P40 Audio Controller

History

I have previously built a very nice DIY Audio Controller and DIY Power Amplifier. The audio controller was build into a plastic enclosure and even utilized a set of DIY Audio Level Meters I had been working on. Unfortunately, the power amplifier board was a demo board sent to me by National Semiconductor and I had intended to create my own custom PCB, but never got around to it, and so it kind of got forgotten about for a while and ran sitting as shown in the photos from that project.

The audio controller used an LM1037N, also by National Semiconductor to switch the audio from 4 input channels. But I also wanted to be able to independently switch one of those signals to the tape deck; that way I could listen to one source while recording another source. The original prototype audio controller used a 4-position rotary switch to signal which input was active, but I decided to use a microcontroller to handle more of the signals I would need in the new design.

Figure 1 shows the reference diagram for the LM3886T power amplifier IC. I wanted to have the MCU control the mute relay (S1), as well as the power to the amplifier board, just like a modern system does. I learned from building the prototype power amplifier that the mute circuit needed to be engaged until after the amplifier powered up to prevent power-on thump of the speakers. I originally solved this in the prototype by creating an R/C circuit that disengaged the mute circuit 2 seconds after the power was switched on.

I decided to designed the overall look of the audio controller and amplifier in a graphics program so that I could mill the enclosures before designing the circuit boards.

More to come.

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Resources

[DOWNLOAD]

Prototype Audio Controller – Project

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BS2P40 Audio Controller by Chris Savage is licensed under CC BY 4.0