Here’s a simple 3 band tone control circuit with 1 transistor instead of using opamps. This is using a single 12V supply. The frequency response is not as good as with using an opamp but it is still acceptable provided you just want a way to boost bass, treble, and mid frequencies. The transistor used is a BC549 but this can be replaced by any general purpose NPN transistor like 2N2222, etc.
VR1 =Treble
VR2 = Mid
VR3= Bass
Simulation result
As expected the response is not as good as what you can get with using an op-amp version but it is good enough for home sound system where you don’t need a very flat response. Each of the controls can affect the whole sound spectrum.
Bass Response at 0%, 25%, 50%, 75% and 100% setting
MID Response at 0%, 25%, 50%, 75% and 100% setting
TREBLE Response at 0%, 25%, 50%, 75% and 100% setting
Extreme settings:
green – bass = 100%, mid = 50%, treble = 100%
red -100%, mid = 0%, treble = 100%
As for the graph above, the mid setting will greatly affect the treble response. This is still good to use is you just want to boost bass frequency.
MIC Preamp type Circuit
The circuit above can be used for mic preamp. This is a simple but not outstanding. The performance is just ok for low end home audio. But for high performance audio, you should go with opamps especially made for audio applications.