Some friends have a need for a volume limiter that can enforce a sound-level curfew, initially the idea was to have a small amp and a big amp and remove the big amp past curfew time (this is at a tiny festival). However that's cumbersome.
I think a better idea is to build into the one amp box a limiter circuit with a keyswitch needed to disable it.
So I came up with:
The clipping devices are white LEDs, and the 7k5 resistors would in practice be internal trimmers or selected on testing.
Switches closed defeats the limiter. When limiting the first stage has gain and the second has matching attenuation. When defeated both have unity gain and the LEDs are at virtual ground so cannot have any effect.
Here's a trace of it with the switches closing halfway through the sim, blue is the output:
I like the virtual-ground aspect of this design, as it removes the non-linear elements completely. I don't like the separate switches having to be switched simultaneously - there's a risk of brief period of extra gain which isn't very polite.
In practice I think I'll use multiple reed-relays to switch, and a master keyswitch to energize them.
The low input impedance isn't an issue as the sources are all phones, mp3 players and laptops, ie earphone level.
However I'm sure there are ways to improve on this I haven't thought of.
[ whoops, meant to post this to line-level, any moderators please feel free to move it ]
I think a better idea is to build into the one amp box a limiter circuit with a keyswitch needed to disable it.
So I came up with:
The clipping devices are white LEDs, and the 7k5 resistors would in practice be internal trimmers or selected on testing.
Switches closed defeats the limiter. When limiting the first stage has gain and the second has matching attenuation. When defeated both have unity gain and the LEDs are at virtual ground so cannot have any effect.
Here's a trace of it with the switches closing halfway through the sim, blue is the output:
I like the virtual-ground aspect of this design, as it removes the non-linear elements completely. I don't like the separate switches having to be switched simultaneously - there's a risk of brief period of extra gain which isn't very polite.
In practice I think I'll use multiple reed-relays to switch, and a master keyswitch to energize them.
The low input impedance isn't an issue as the sources are all phones, mp3 players and laptops, ie earphone level.
However I'm sure there are ways to improve on this I haven't thought of.
[ whoops, meant to post this to line-level, any moderators please feel free to move it ]