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