Marshall JCM 900 SL-X Review

For this article a review for the Marshall JCM 900 SL-X, the 50 watts head version of this amplifier. This amp was made by Marshall between 1993 and 1999. The design of this amp is loosly based on a modded JCM 800.
The name SL-X stands for Super Lead Extended.
The SL-X is a one-channel amp which contains two master controls which you can set-up for different volume levels. You can access the different channels by using a latch footswitch. Any general latch-footswitch can be used to toggle between Master Volume A and B. Unfortunately the amp does not contain two sets of tone controls since the SL-X is just a one channel amp.



Footswitch    Prescence  Bass Middle Treble Master Vol. B Master Vol. A  Gain         Pre-Amp
Master Vol. B                                                                                  Sensitivity     Vol.

For anyone familiar with Marshall amps these controls look quite familiar as most Marshall amps contain similar tone controls. Like with any Marshall, the treble is the most active tone-control, bass and middle are there to enhance your sound, similar to the prescence control. To fine tune your tone controls you may want to use an external EQ pedal to add a bit more body to the overal sound of the SL-X

Looking at the controls you will notice something unusual: A Gain and a Pre-amp control, which are basically two pre-amps. These two pre-amps add  most of the character to this amp: You will need both of them to be turned up to get any sound  out of the amp.
The Gain control adds more treble to the amp, this is the control which adds a more modern touch to the sound of this amp. On moderate settings this control can give you the crunch sound of the 90s
The Pre-amp control adds a darker sound to the amp: Using this control mainly and you will be able to get the sounds of the Plexi and JMP Marshalls from the late 60s and early 70s.

At the back of the amp there are two direct outs: one for plugging into a power-amp and one to be plugged into a mixer or recorder or anything of that kind. There is an effects-loop as well, which can be used  for plugging in any rackbased kind of effects. For stompbox-based effects you may want to plug them directly into your input at the front of the amplifier.

  Marshall: Max Out All The Contols!!:

Anyone into playing electric guitar will have heard this comment before but hang on: Most of the time when guitar players max out all their controls it will also destroy the tone and character of the amp. Yes, maxing out the controls will make the amp loud, very loud indeed, but that is all you will get as most of the subtle  character of your sound will be lost.

Is there no truth in the comment than at all? Yes there is some truth in this comment but it relates to older amps, most likely to amps of the 1960s which only had one volume and some tone controls. Turning up the volume on any of  these amps will create power-amp distortion, which most guitar players seem to like. Turning up the amp will create this power-amp distortion.

Looking back at the controls of the SL-X you will notice both pre-amps, turning these up will add character to the distortion, the master can be used to adjust the volume to taste. Most of the character of the sound is in the pre-amp controls, there is no need to turn up the master to add more distortion.  In most cases you will want to adjust the volume to the room where you play: Playing in smaller room you will probably not need much volume to get the sound you like whereas using the amp on a stage it will be likely that you will turn the amp up a bit more to get the sound you want. Logical eh?

On a side-note: Remember why distortion pedals were designed orginally? To mimick the power-amp distortion to create distorted sounds on a fairly low level.

     Speakers and Valves:

Originally the SL-X was equipped with 5881- or EL34 valves. You can experiment with different valves as it will make a change to your overal tone.
The amp I used was set-up with its orgininal 5881’s. I used the amp in combination with Celestion speakers: a Vintage 30 and a G12H. This combination seems to work quite well for this amp.
When it comes to speakers, you can use any speakerset you like, however Celestion speakers add to the character of the Marshall sound. Marshall has been using Celestion speakers since day one. Experiment with different kind of Celestion speakers to find the ones you like most of all.
If you want to change the type of valves, be careful: The amp may need rebaising. It may be an idea to get advice from an experienced amp technician.


Experimenting with the settings of the SL-X you should be able to go from Crunch into Classic Rock, Early 80s Metal and more extreme versions of Metal. The amp is also great to get-just broken up- blues sounds.
Overal I feel this amp will give you access to the older and newer Marshall sounds.

For next blog I will go into detail how well the SL-X responds to various pedals and to guitars equipped with different pick-ups.

Hope to see you soon again,