Pre-Amp Circuit

Front of the amplifier is done by the Op-Amp A1, this is the amplifier A1 is actually a time, with the intention of utilizing the high input impedance, about the size of 1M, from one specification data suggest op-amp for use with high-frequency dynamics, the input impedance is too large will degrade its stability, therefore the potentiometer (Pot1) of 47k is used to ensure impedasi input circuit, an audio standard value (real 50k), if the reader wants an application with a larger input impedance, use the value of Pot1 higher, it is recommended to not exceed 220K. Pot1 is also acting as a regulator of the audio volume level.

Originally wanted to eliminate all coupling capacitances in this circuit, because the ability of op-amp for direct copling DC. The capacitor C1 is placed as a fixed coupling, with the intent as described above, the reader may wish to modify this circuit. Capacitor C1 together with Pot1 form a filter to pass over (high pass filter). 100N values ​​are set not so much to blame, if readers want to do use the following formula to calculate the value of C1:
 F = 1 / (2 * 3.14 * C1 * Pot1) (Hz)
 Set cut-off frequency F as desired, usually 50Hz or 60Hz to eliminate the frequency of wild llistrik network. Setting the tone carried by the loop-amp A2 which also acts as an amplifier with positive feedback, divided by two, partly channeled into a series of R1, R2, C2, C3, and Pot2 separately adjust the gain of low frequency (bass), and partly supplied to the circuit C4, C5, and Pot3 to adjust the gain of high frequency (treble). Furthermore R3 and R4 mixing (mixing) back to form a positive feedback loop earlier. Frequency regulation such as this is a frequency filter Baxandall Theorem, can be regarded as the standard audio to date.

The use of IC op-amp TLO74, because this component is cheap and easily available, and most importantly, this IC belt use JFET input and a high slew-rate. With the above circuit the reader can enjoy the stability of a low tone (Bass), agility tone middle (Mid), and the clanking of his high notes (treble).