Solid State Guitar Amp Forum | DIY Guitar Amplifiers
Solid State Amplifiers => Amplifier Discussion => Topic started by: Bear on May 13, 2015, 10:46:57 AM
I picked one up for a song and don't need the schematic yet, but better to be ready. The JX-20 and -50 can be found online, but not this guy for some reason. I presume I can extrapolate from those and visual inspection, but figured there was a chance someone here might have it.
Great little amp, BTW. I bought it expecting it would give the blackface/silverface feel that it does have in spades, but I was surprised at how decent the pull-boost overdrive is.
Finding that service manual might prove to be difficult. Here is a JX30 that you can look at too.
According to my schematic archive JX50, JX40, and JX30 have practically identical preamp sections. Maybe JX25 does as well.
Pretty much a plain shunt diode clipping arrangement for O/D tones: Switch provides more voltage gain pre clipping diodes (thus more overdrive) and more low-pass filtering post clipping diodes (thus "smoother" O/D tone with less annoying high frequency "fizz").
Few points worth noting: 1S1555 diodes has few hundred millivolts higher forward voltage than a generic silicon diode. ...If there even is such a thing as "generic" silicon diode. A failry high series resistance is employed post clipping to limit diode current. These features provide a moderately "soft" clipping performance.