P1______________47K Log. Potentiometer (See Notes) P2,P3___________47K Linear Potentiometers R1,R3,R5_________4K7 1/4W Resistors R2______________22K 1/4W Resistor R4_______________1M 1/4W Resistor R6_______________1K8 1/4W Resistor R7_____________560R 1/4W Resistor C1,C4,C5,C7_____10µF 63V Electrolytic Capacitors (See Notes) C2______________47nF 63V Polyester Capacitor C3_______________1nF 63V Polyester Capacitor (See Notes) C6_____________220µF 35V Electrolytic Capacitor Q1____________BC550 45V 100mA NPN Low noise High gain NPN Transistor
A Bass and Treble frequency control to be added to the 3 - 5W Class-A Amplifier was required by some audio enthusiasts. Therefore, this circuit has been designed keeping in mind the extreme simplicity of the amplifier circuit to which it should be linked and was carried out using as few as components possible.
Q1 is the only active component forming a straightforward single-stage transistor amplifier with the tone control network in the ac feedback path. Taking this feedback from the split load of Q1 we obtain an ac stage gain of about 3: this can be useful to cope with low output voltage audio sources.
- Input sensitivity:
- 160mV RMS for 0.5V RMS output
- Input impedance @ 1KHz:
- Volume control knob to 12 o'clock = 40K
- Volume control knob to 2 o'clock = 19K
- Maximum output voltage:
- 4.5V RMS into 10K load
- Frequency response:
- flat from 15Hz to 23KHz
- Total harmonic distortion @ 1V RMS output:
- 1KHz = 0.008% 10KHz = 0.01%
- Total harmonic distortion @ 4V RMS output:
- 1KHz = 0.06% 10KHz = 0.05%
- Bass control frequency range referred to 1KHz:
- +11.6dB/-8db @ 100Hz
- Treble control frequency range referred to 1KHz:
- +7.7dB/-7.3dB @ 10KHz
- Treble control frequency range can be increased to +8.7dB/-9.9dB by raising the value of C3 to 2n2.
- C1 and P1 are the components with the same labeling already existing in the 3 - 5W Class-A Amplifier.
- C7 is an already existing capacitor labeled C2 in the 3 - 5W Class-A Amplifier. Please note that its polarity must be reversed.
- The circuit is powered by the same 24V supply line of the 3 - 5W Class-A Amplifier.