This is a bass booster circuit that use transistors as base. It is designed to increase a low frequency of audio on cheaper than ICs or normally circuit.
These are Tone control circuit using op amp - NE5532 or 4558 IC as low noise, with PCB layout, can adjust sound frequency and tone bass, treble, mid and..
These are many pre tone control circuit, use transistors as main. so low noise,good sound, cheap and easy to buy parts, you can builds with PCB layouts
The Passive tone control circuit, to adjust bass-treble with no the expansion, use equipment R and C only, to filter frequency,easy without power supply! [...]