I am trying to construct a small 5W guitar amplifier with tone control as an introduction to audio electronics.

I have taken two openly available circuits and I am trying to reverse engineer and combine them.

Circuit 1 I believe is a TL082 pre-amplification stage with tone control at op-amp output.

Circuit 2 I believe is an LM386 based power-amp circuit that I want to feed circuit 1 into.

As I understand it a common configuration is (pre-amplifier->tone control -> power amplifier,) where the LM386 is acceptable for low/battery power-amplification.

I was hoping for some guidance:

  1. What is the purpose of R45 (1milliOhm) in the pre-amp circuit? As the circuit image as taken was made to do a PSpice simulation I wonder if it was intended to be a potentiometer to adjust pre-amp gain. In my circuit can I just exclude or short this, as a gain potentiometer will be provided at the beginning of my power amp circuit? I believe the diodes in parallel are for "soft clipping" to achieve a signal warmth?l.

  2. Am I correct that I can combine these circuits by feeding the output of the pre-amp/tone circuit to the LM386 power amplifier circuit? Say, by feeding circuit 1 output from R45 into circuit 2 J1 input.

Any advice is greatly appreciated

Circuit 1, TL082 pre-amplifier and tone control:

enter image description here

Circuit 2 LM386 power amifier with some extra bells and whistles:

enter image description here

  • 2
    \$\begingroup\$ The LM386 is a one watt amplifier. You can't get 5W out of it. \$\endgroup\$
    – JRE
    Jul 31 at 18:04
  • 2
    \$\begingroup\$ R45 is 1 Meg ohm, not milli ohm and defines the gain together with R46. \$\endgroup\$
    – Jens
    Jul 31 at 20:03
  • \$\begingroup\$ @Jens Thanks, I had that suspicion but as you notice it uses lower case m. This makes more sense. \$\endgroup\$
    – GodJohnson
    Jul 31 at 22:02
  • \$\begingroup\$ @JRE Thanks for that I had not noticed that when choosing the LM386. I will continue with a 1W design, and make it a goal to spec out a different op amp and circuit and circuit for 5W after successfully completing this project. \$\endgroup\$
    – GodJohnson
    Jul 31 at 22:04
  • \$\begingroup\$ The input jack J1 of the amplifier looks like it is reversed. The signal should be on the tip and the ground on the sleeve. I have seen similar errors elsewhere. \$\endgroup\$
    – PStechPaul
    Jul 31 at 22:15


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