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Marshall JMP-1 Tube Guitar Preamp

Marshall JMP-1 Tube MIDI Guitar Preamp
Marshall JMP-1 Preamp

The Marshall JMP-1 is a tube guitar preamp that is based on the sound of Marshall amps. It’s housed in a very well built 19 inch rackmount. It uses two ECC83 preamp tubes to create its various amp simulations. These are fairly accurate sounding and come with a speaker output emulator for connecting to a recording board. It’s great for any guitarist who doesn’t like hauling the weight of stack around or who wants 100 different sound amps in one box. This is not an ‘effects’ processor and has no chorus, delay or other effects. It’s a tube preamp made for guitar.

The four input channels are labeled, Clean 1, Clean 2, OD1, and OD2 (OD means OverDrive). These channels aren’t really switched between as they are used to program ‘presets’ of which you can switch between. The MPM4E 4-way footswitch allows you to change between 4 presets, where each button is assigned to a preset. The footswitch outputs are fixed by you can ‘re-map’ them to any of the 100 presets in the JMP1 (see below for more info). Clean 1 is just that very clean yet does have a sense of warmth to it. You can get a slightly overdriven sound from this channel which is great for clean sounding leads. Clean 2 is a little bit hotter with some added high end presence. It is said to sound like an early JTM45 or SLP at lower non-distorted levels. OverDrive1 is where you really start to hear that Marshall Sound. It’s very potent and sounds like that of an SLP and sounds great with a Strat or Les Paul. Good vintage blues sound with a modern edge to it. OverDrive2 is more modern sounding with a very aggressive tone that is great for Metal or everything else. This is the highest gain channel of them all.

Programming the unit is very simple using the data knob and the 14 parameter type knobs located on the right hand side of the unit. The parameter types are Gain, Volume, Treble, Bass, etc… which makes it very easy to edit. You don’t have to go digging in to the menus to change your sound. You can change patches on any one of the 100 presets. The first 25 preset where designed by professional guitarists and can be changed and written over. The system can be re-initialized back to the original somewhat easily. To program you select the preset number, select which channel type (OD1, OD2, etc…) then set the Volume, Gain, and EQ controls. Again each parameter has its own button which makes it much simpler to edit. One slightly obscure option is the Bass Shift button. When in use it thickens the bottom end of the sound. It gives you a tighter sound and feel as well as low end for metal.

The unit also has a parallel mono send and stereo receive FX loop. One thing I noticed is it puts out a good loud signal which is good because it can be used with a number of different effect processors. There is a level switch that allows you to select between +4dB and -20dB output send. The ‘Effect’ button on the front panel allows you to program the level of the effect within patch. This level setting is more of a direct/effect balance knob than a simple level setting as turning it to 12 (range 0 to 12) only the effects are heard. Most guitarists will probably plug their delays, and reverbs through the effects loop and run their guitar and mono effects, ie. compressor, volume pedal, and noise gate, and plug it into the JMP-1’s input. If you are using MONO only effects then use the left return jack only.

There are two sets of outputs which are meant for two different types of inputs. The normal Master outputs are used for connecting to a power amp. The power amp can be anything from a guitar power like the Marshall EL-34 50/50 to a PA power amp.

The outputs are unbalanced ¼ inch connectors. There is however a +4dB/-10dB level switch on this output. This allows you to set the output level to match your system. Most guitarists will probably use the -10dB output level setting however. There is also a Marshall Speaker Emulated output which has been EQ’d to make it sound more like what a guitar speaker cabinet would sound like. This is used for connecting directly to a mixing console or DAW input and sounds. You may find that some post EQ on your mixer may be required to get your sound. One thing about the emulated output is its output level is controlled by the Volume Key control button that is located inside the preset you are using and not by the volume control on the front panel. The front panel volume control is used to set the level of the Master outputs which are usually sent to your power amps.

You can change patches from the front panel, or by using the optional Marshall 4-way footswitch (the MPM4E). You can also change patches using your own MIDI controller, Sequencer, or MIDI Foot-controller. The JMP-1 uses MIDI to change the patches while playing. You simply tell it which MIDI channel to read the patch change commands from and it does the rest. It will also send out a MIDI program change message when you change the patch on the front panel. It has the ability to change or re-map MIDI program changes to a different number. This is useful depending upon how your system is setup. Some MIDI footcontrollers for instance output a FIXED program change number which probably doesn’t match what you would like it to. Remapping the Input in this way allows you to use a different patch number for the MIDI program change number. For instance say you wanted to assign MIDI program change #12 to preset #47 in the JMP-1. So each time the program change #12 is received the JMP1 will change to patch #47. This is also useful if you changing presets on other Guitar Related Effect processors or multi-effect processors.

There is also a MIDI output re-mapper that allows you to re-map what is coming out of the JMP1’s MIDI output. This is great when you want to use the JMP1 as the master effects patch changer. This means that every time you change the patch on the JMP1 it sends out a MIDI program change out its MIDI output which, for example, could have a multi-effects processor connected to it. Re-mapping its output allows you to assign each patch in the JMP-1 to a different patch in your effects processor. For example say you are using patch #19 and you want to use it with patch #121 on your multi-effects processor you would use the output re-mapper to do this. Every time patch #19 on the JMP1 is pressed then the MIDI program change #121 is output to the multi-effects processor. These re-mapping assignments are remembered when you turn the device off but are erase if you re-initialize it. Also MIDI program changes can become problematic when trying to access above 127 on the JMP1. So if you are using an fx processor which has more than 127 presets you will probably have to copy the presets located above 127 in the fx processor to presets numbers between 0 and 127.

This is an excellent guitar preamp. It cost slightly more than other preamps but it is worth it especially if you are interested in the Marshall Sound and brand name.


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