Marshall JCM900

Note: the modifications / upgrades listed here are a guide to services we offer and should not be undertaken by novices.Valve amplifiers contain high voltages which can cause death .

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MARSHALL JCM900

LUCAS MILES AUDIO

AUSTRALIA

The Marshall JCM900 series of amps were released 1991 , following in the footsteps of the JCM800 series. The designers at Marshall obviously thought they could create a similiar tinny, chainsaw sound like the JCM800 by mixing op-amps with tubes in the preamp stage of the JCM900 , thus eliminating costly tube circuitry , utilising smaller power and o/p transformers and overall saving costs and making the company more money which means bigger Xmas bonuses..Alright!!!.. What they created is probably Marshall at its lowest point .A series of amps notoriously toneless and thin. Smart JCM900 owners bypass the Preamp stage and run an external preamp / processors into the FX return , thus only using the output stage of the amp for there sound. Good idea.

The Marshall we look at here is a JCM900 4500 Dual Reverb 50w Head.

	Here we have the internals of the JCM900. Two main boards. the preamp board at the front and the output / power stage at the rear . Reasonably easy to access and service.

On the right , the input stage . Just when you've thought you've bought a classic Marshall valve amp, you plug your guitar in and what does your signal hit first.....a pair of op-amps. Uh-oh. ..not a great start .....and it doesnt get any better...

	More op-amps in the signal chain . Both the lead channel and the normal channel run through three op-amp stages before they even get close to hitting a tube .But the damage is already been done.The tone has no body or depth.

With a small upgrade to the tone capacitors we can eliminate some of the accentuated trebles and try and add a bit more body to the sound.

	The o/p board showing the orange coupling capacitors in the o/p stage.These were upgraded to Sozo capacitors , once again in a desperate effort to extract a bit of tone out of the JCM900.

And for the end result . Well the Marshall JCM900 4500 split channel is just a glorified valvestate. Our modifications did change the sound for the better but if we had a choice .....the JCM800 series is a way better alternative.