From Jon: The Bearhug is a (fairly) low-parts-count, quiet, tonally transparent compressor using only transistors. It can do subtle peak limiting or squishy sustaining, with a decent amount of boost (probably ~6-12db).
Notes & mods:
- The hold cap is the reversed 4.7uF. This sets the overall compression and decay. The 10K + 47K in parallel with the hold cap set the decay. Larger values may be used, but these were the most natural sounding overall.
- The High/Low switch is there for "more." A 100K instead of the 47K would provide a much more dramatic change.
- You can use substitute Schotkey, germanium, or other diode with forward voltage under ~.35v for the 1N60Ps.
- The best tone control for this circuit, if you want to add one, is Jack Orman's version 2 of Mark Hammer's SWTC.
- The 100pF cap is primarily to eliminate noise and can be adjusted to change the overall brightness.