This preamplifier was designed as a stand alone portable unit, useful to control the signals generated by guitar pickups, particularly the contact bug types applied to acoustic instruments.
http://www.redcircuits.com/Page69.htm
The aim of this design was to reproduce a Combo amplifier of the type very common in the sixties and the seventies of the past century. It is well suited as a guitar amplifier but it will do a good job with any kind of electronic musical instrument or microphone.
http://www.redcircuits.com/Page52.htm
Guitar amplifiers are always an interesting challenge. The tone controls, gain and overload characteristics are very individual, and the ideal combination varies from one guitarist to the next, and from one guitar to the next. There is no amp that satisfies everyone's requirements, and this offering is not expected to be an exception.
http://sound.westhost.com/project27.htm9
The amp is rated at 100W into a 4 Ohms load, as this is typical of a combo type amp with two 8 Ohm speakers in parallel. Alternatively, you can run the amp into a quad box (4 x 8 Ohm speakers in series parallel - see Figure 5 in Project 27b, the original article) and will get about 60 Watts.
http://sound.westhost.com/project27.htm
Each channel has a master volume which enables it to be clean or with overdrive. The switching is done with relays and has a jack in the back for a foot switch. There is a red and green LED indicator on the faceplate to determine which preamp is on.
http://europa.spaceports.com/~fishbake/gamp/40watt.html