A “night mode” volume switch for the BBC Master
BBC Micros are great, but the volume level was clearly intended to compete with a classroom full of noisy children. When playing games at night, the sound output is far too loud.
It’s possible to wire in a volume control, but that would require breaking into the audio circuitry to intercept the signal before the output amplifier IC. I didn’t particularly want to do this, and didn’t see the need for continuously variable output anyway.
I also didn’t want to modify the case by drilling holes in it for potentiometers. Instead, I used the small square cutout by the expansion bay. This doesn’t lend itself well to mounting a switch though, so a small 3D print was needed to accommodate a miniature slide switch I had in my spare parts box. This switch can be used to add a resistor in series with the loudspeaker to reduce the volume.
![](https://jamesholden.net/wp-content/uploads/2023/03/circuit-1.png)
I found by experimentation that a 100R resistor was enough to quieten the volume down significantly. The switch, when closed, bypasses the resistor and restores full volume.
![](https://jamesholden.net/wp-content/uploads/2023/03/IMG_2158-1024x768.jpg)
The switch fits nicely in the cutout, as seen from the inside.
![](https://jamesholden.net/wp-content/uploads/2023/03/IMG_2160-1024x768.jpg)
Outside, the switch is visible but unobtrusive. The line across the print is where I paused printing to insert the switch, rather than using the tiny mounting holes on the tabs at either end.
![](https://jamesholden.net/wp-content/uploads/2023/03/IMG_2159-1024x768.jpg)
The internal wiring is nice and neat and easily removed if the volume control is no longer required. I had a spare two pin connector to fit onto the main board speaker connection, and used a two pin PCB header to connect to the speaker connector. The resistor is hidden in the heat shrink tube next to the speaker connector.