OK, WE KNOW THAT most guitar amplifiers have a headphone socket that you can use for a quiet practice session at night but who wants to have to switch on a hulking big amplifier just to listen to headphones? Also playing guitar via the headphone socket on many amplifiers is not that great. Often there is quite a lot of hum and buzz and it often doesn’t sound particularly clean either.

Nor do guitar amplifiers perform all that well with the high level signals from a CD player. So we have come up with a low cost and compact headphone amplifier with mixing for the signals from a guitar and a CD player. For economy the headphone drive is mono, from a single LM386 IC amplifier. It can be pow-ered from a 9V DC plugpack or a 9V battery. Either way, the sound quality is surprisingly good considering the simplicity of the circuit and it is certainly better than the sound from the head-phone socket of most guitar amplifiers.

Actually, the idea is not new. We picked up the idea from an article on a "Guitar Jammer" in the July 1998 issue of "Popu-lar Electronics". This was also based on an LM386 but we have refined the circuit in a few aspects and produced a new PC board with all the components, including the pots and jack sockets, on the board. The circuit is also similar to a headphone guitar amplifier we published in the May 1995 issue but that circuit did not include mixing facilities.

Input facilities

The Guitar Jammer is housed in a compact plastic box and has two potentiometers for setting the input levels for the CD player and guitar. It has two 3.5mm stereo jack sockets, one from the CD inputs and the other for the headphone output. The 6.5mm jack socket is for the guitar lead. The circuit will drive virtu-ally any stereo headphones, whether they are 400Ω, 32Ω or 8Ω, although the best bass will come from headphones with full ear-enclosing muffs.