12
12
MGP-1A Advanced Modeling Guide
Crunch
UK800
Mod
Deep
Bright
EQ
Shift
Alt
EQ(-)
Citrus
Cali
Crunch
Mid
Bass
Treble
Volume
JCM800 Mods
The JCM800 is also arguably the most modified amplifier in history. Most of these modifications are
aimed at making the amplifier less bright.
One of the most common mods was to remove the bright capacitor which you can do by simply turning
the Bright Switch off. Another common mod was to increase the low end amplification ability of the first
tube. We felt this method sounds flabby, so we modified the mod to target the low mids which is great in
this model and helps us model a later Marshall amp’s tone.
A very common mod that was performed to these amplifiers is to modify the tonestack so the treble
control gets into the mids more. Use the EQ Shift for the same effect.
Power
Tubes
: EL34 or 6550, Push Pull
Speaker
Cabinet
: 4 x 12” Celestion G12T-75 (1960), V30 (1960V), G12-80 or G12H-100 (1982x)
Crunch
UK800
Mod
Deep
Bright
EQ
Shift
Alt
EQ(-)
Citrus
Cali
Crunch
Mid
Bass
Treble
Volume
JCM800 ( Model 2205) Boost Channel
This amp has much more distortion than the classic JCM800 circuit, but it does so with clipping diodes.
Many love the gain, but hate the tone and remove the diodes. We instead emulate this with tube gain,
which gives a much more natural and smooth tone, while retaining the “Marshall sound”. The tone stack
used in this amp has an isolated midrange control, which makes the bass and mids a bit stronger and less
interactive, perfectly complimenting the higher gain.
Power
Tubes
: EL34, Push Pull
Speaker
Cabinet
: 4 x 12” Celestion G12T-75 (1960x), V30 (1960xV), G12-80 or G12H-100 (1982x)
Marshall
Marshall
®
JCM800 (Cont.)
