Preamplifier Guitar Control Circuit

Parts List

The circuit has been designed for the purpose of creating a portable unit of preamplifier that would function as standalone control for gutitars.

• TL062 – a low power JFET dual operational amplifier where each op-amp incorporates well matched, high voltage JFET and bipolar transistors in a monolithic integrated circuit and with features such as low input bias & offset currents, high slew rates, low offset voltage temperature coefficient, high input impedance, high gain bandwidth, output short circuit protection, large output voltage swing, internal frequency compensation, and latch up free operation
• Operational Amplifier (Op-Amp) – a DC coupled high gain electronic voltage amplifier with differential inputs, large voltage gain, very high input impedance, low output impedance and usually a single output

The circuit contains a three-band tone control and a three-level input selector while being powered a 9 V battery source. The signals generated by guitar pick-ups can be controlled by this circuit specifically pertaining to the contact bug types being applied to acoustic instruments. This shows that the circuit can be used with any type of pick-up and instrument. In order to deal with almost any type of model and pick-up, the input selector is made to adjust the input sensitivity by featuring a -10 dB, 0 dB, and +10 dB preset value. Since the circuit is consuming low current, the life span of the battery is ensured to last for longer time.

An inverting amplifier is formed using the op-amp IC1A with the three way switch SW1 setting the gain for this amplifier. This is made possible by inserting different resistors with different values in parallel to R4. An active three band tone control stage consisting of the bass, middle, and treble, follows the input stage and are being regulated by linear potentiometers P1 to P3. When the band controls are set in their center position, they produce a unity gain while being built around IC1B.

The frequency response of flat controls ranges from 20 Hz to 20 KHz. Tangs ranges of tone control frequency is 15 dB at 30 Hz, 19 dB at 1 KHz, and 16 dB at 10 KHz. The total current being drawn by the circuit is less than 800 uA while the total harmonic distortion at an output of 1 V RMS is less than 0.01% although the maximum undistorted output voltage of the circuit is 2.5 V RMS.

The preamplifier guitar controls in the market are normally having settings for input gain, tone equalizer, and master volume/gain control. There are guitar preamplifiers designed for acoustic guitars or brasses and they are usually equipped with 3 to 4 tone controls. Some are designed as an acoustic guitar preamplifier that works in a way to handle conditions in acoustic or live environments. Other features that this circuit may acquire are the ground lift selection, amplifier selection, drive control, and earphone monitor.

Source:redcircuits.com/Page69.htm