MARSHALL MODIFICATIONS:

The following modifications can be installed in most Marshall amplifiers starting with the JTM-45 and all later models including some JCM 800 models. The vintage reissue series is highly recommended. We feel these Marshalls sound as good as the originals and are more available and usually less expensive than vintage Marshalls. All of the amp upgrades discussed in the amp repair and mod section apply here.

BASIC PREAMP MODIFICATION

This modification is our flag ship Marshal amp mod. You have probably heard it on any number of hit recordings: Robert Palmer Band, Rolling Stones, The Cult to name a few. The mod begins with a complete overhaul. We then install the power supply mod (see Amp. Mod. section). Next, a high gain, high headroom very low noise preamp is built into the front end of the lead channel. Both of the original input channels are restructured and tone contoured. The second or rhythm channel is set up to resemble a good clean JTM- 45 sound. The Presence control is moved to the rear panel and a Master volume control is installed in it's place.

CHANNEL SWITCHING MODIFICATION

A front panel switch and stereo footswitch selects three channels: clean, crunch rhythm and lead. This mod can only be installed as an add on to the basic preamp modification. A second drive control is added for the crunch rhythm channel. High speed reed relays that provide instant and quiet switching are used for all switching functions.

SELECTABLE GAIN PREAMP

This is an option that can be included in the basic preamp modification. This front end preamp comes with a front panel 3 position switch that selects a 15 db boost (5X) or a 15 db treble boost over the normal gain of the preamp.

IMPEDANCE SELECTOR SWITCH

The impedance selector is replaced with a high quality industrial/MIL SPEC switch. The ceramic base constuction and heavy duty gold plated contacts eliminates distortion and drop-outs that plague plugs and consumer grade switches. And unlike plugs this switch doesn't get lost just before soundcheck.