If you love to pump up the bass then this would be great project for your sound system. This is based on my previous tone control design with some modification to give more deeper and louder bass. It is basically the same with modified component values.
ABOUT THE CIRCUIT
The signal amplifier circuit is composed of R1-R4, C1, C2, C7, and Q1. It is configured as common emitter amplifier. It amplifies the signal because it will be attenuated on the next stage. R4 and C1 is used as low pass filter to filter out the low to high frequency ripple voltage of the power supply. It basically cleans the power supplied to the circuit. C2 and C7 is used to remove DC offset from the transistor bias. They are DC blocking capacitors, it passes AC and blocks DC. R2 is used to bias the base of the transistor to set the voltage of the collector to somewhere around the middle. R1 and R3 sets the gain of the amplifier. To increase the gain, decrease R1 or increase R3. Always check the bias levels after changing the value of R1 and/or R3 as this might result to signal distortion.
CIRCUIT SIMULATION
Simetrix is used in this simulation. A free simulation software for individuals.
Bass Response
The problem with this kind of circuit is that the frequency response is not linear. The graph below is sweep from 10% to 100% bass setting with 10% interval while the treble is set to 50%. As you can see, the response is almost flat around 10% bass setting instead of 50%. It has around 12dB of bass boost at 50% bass setting.
Treble Response
Below is the frequency response of the treble control with the bass set to 50%. There is 12dB bass boost at 50% bass setting. The treble setting start at 10% all the way to 100% at 10% increment.
Adding output buffer
The problem with this circuit is that it changes frequency response with the next stage input impedance. If the amplifier has a volume control, it affect the frequency response.
