Guitar preamp circuit – over drive using 12AU7

This Guitar preamp circuit is a guitar booster for those with a love for music. act as preamplifier or over drive signal acts soft voice before to the power amplifier or headphones. Highlight is a very clear sound without noise. Because we use 12AU7 vacuum tubes is the main equipment, which is better than any other preamp circuit. It also easy to builds because of the a few parts.

the Guitar  Preamp - over drive using 12AU7

Figure 1 the Guitar Preamp – over drive using 12AU7

How it works
In Figure 2 is circuit diagram. When We play the guitar, micro phone or contact will get sound signal from the electric guitar to J1. Then coupling through a capacitor-C1 to a grid pin of 12AU7 vacuum tubes-V1/1, by have a resistor-R1 is setting an input impedance of them, and has VR1 act as resistance of cathode to set bias current of vacuum tubes V1. When the bias is changed cause gain also changed so Operating VR1 adjusts the sound as we played guitar.

the circuit diagram of Guitar  Preamp - over drive
Figure 2 the circuit diagram of Guitar Preamplifier – over drive.

The first signal section will coupling through capacitor-C2 to grid of V1/2, which is the final preamplifier. Then coupling through capacitor -C3 to VR3, Which acts as the volume for adjust the output level of J3. To application to headphone or guitar power amplifier in sequence. The capacitors C4 and VR2 will adjusted the tone according to the user needs.

How to builds

After collecting the the necessary parts in this project. Then prepared completely the PCB as Figure 3 PCB layout.
The PCB layout of  Guitar  Preamplifier
Figure 3 The PCB layout of Guitar Preamplifier

The next step consists of the device as shown in Figure 4 is components layout. Starting from several points short circuit wire. Then resistors The eyelet for soldering wires. Next capacitor. But because this circuit using less amounts. As a beginner, it can be assembled quickly.

the components layout
Figure 4 the components layout

Later, the small PCB for install vacuum tubes soldered to the socket for the bulb first, followed by a perpendicular connector. Then take the small PCB to the main PCB again.

The final step is to install all three volumes and Jack inputs and outputs. Including input jack for DC power. It may test the wires to the outside before. If we have any problems going to be solved easily.

Testing and application

Since this projects have less parts. And have test point a little. If the circuit is correct, nothing wrong. We created this project to be able to run the course. Before apply dc power supply to this projects should disconnect the tube is V1. Then begin to apply voltage to circuit. Next use voltmeter to measure DC voltage at pin 5 of socket on PCB compare with ground of circuit. It must near supply voltage, because it serves the heater, then plug the tubes into the socket packet tightly.

Reductions VR3 low volume, then enter the signal from the guitar to the point J1, And the the output signal from J3 to the amplifier or headphones to test it. Adjustment of VR3 the volume up a few. The experimental electric guitar, listen to the sound that out of the output signal. If have one it indicates that the project can work normally.

If no signal is found, remove power, then check the soldering equipment that the various loose. Assembly and the tubes socket to tighten it, there is heater voltage. The various signals point, wires, must completely. Then check step by step until the circuit worked normally.

The components list
Resistors ½ watts +-1%
potentiometer resistor has a single class, short axis.
VR1_________50K (B)
VR2, VR3_____100K (A)
Capacitors (polypropylene)
C1, C2________0.047uF 400V
C3___________1uF 400V
C4___________0.01uF 400V
LED1___ LED 3 ??. Red
Other parts
V1______ 12AU7 vacuum tubes with socket.
J1, J3____ Jack Mono.
J2_______Jack DC in.
Universal Box, Knob, small wires, shielded mono cables, etc.

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This Post Has 9 Comments

  1. Can I purchase the PCB board and how much.

    Were can I get it, and how much is it, need two.

    Thank You.

  2. Hi, Dr.warren layfleld.
    Thank for your feedback.
    I cannot sell PCB to you.
    I am sorry.

  3. can this be use with a 14 volt power source? if not, what can be done to the circuit to do so?

  4. I am thankful to you for your continuous mailing me.
    Do you sell kits of projects published here also?

  5. What are the dimension of pcb layout of this project?

  6. Nearly all these circuits on this website and many more websites by the same author are copies of other peoples circuits. This author is a prolific copier and states that he is ‘Innovative’. He copy’s others work and pretends it is his own.
    How about you make your own circuits and post to youtube where there is a big audience. I do not suppose he will as others will see their work and thumbs down and maybe pass comment.


  7. Can u run a 12ax7 with this circuit and use higher voltage. i see you are using
    high voltage capacitors but this circuit is only suppose to run at 9v.

  8. Why on earth use 400V caps in the signal line (for coupling)? Use good polyies of lower voltage …

    1. Hello JernejQ,
      Thanks for your feedback.
      I feel sorry that can help you. I never test it in real use.

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