#097 Volume Control Power Amp

An LM386 fixed-gain audio power amp with volume control.

Notes

This variant in the line of LM386-based amplifiers is based on a design in Beginning Analog Electronics through Projects.

It is similar the Little Gem/A386, but with a few differences:

• The LM386 gain is actually fixed at 200x with 10μF C5, with volume control on the input provided by R1.
• it adds a small RF-bypass capacitor C2 to prevent RF-breakthough of radio signals
• the output coupling capacitor is slightly smaller at 10μF
• additional 100nF low-pass filter on the power supply

How it performs:

• the input volume control works fine, although it is pretty redundant as it is ding the same job as a guitar’s onboard volume control
• the RF-bypass capacitor does appear to give a cleaner signal
• the lack of gain control means the overdrive level is fixed. It’s a pretty nice and warm effect that cuts in with higher input volumes

Construction

Credits and References

• Based on “Project 05 - Variable-Gain Audio Power Amplifier” from Beginning Analog Electronics through Projects
• my LittleGem/A386 build
• Smokey Amps - official site
• Smokey Amp Analysis - excellent circuit analysis of the original Smokey amp.
• Observations on the Smokey circuit by Dave Stork
• LM386 datasheet