Marshall JVM 205 mod to Classic Rock amp

I liked my Marshall JVM at first but after a while it just seemed to be stiff and more like a transistor amp, that tube amp mojo just seemed to be missing. I tried many JVM forum mods to get the amp to sound less stiff but none seemed to work. I almost gave up in frustration until I noticed a radical departure in the design of the JVM amps. The Gain volume pots have super super super high values for the bright capacitors! This lets in bright mids that cannot be dialed out. By reducing the bright caps to allow only high frequencies the mids fell back into balance with the bass and treble. The stiff transistor character of this amp was gone (well at least 90% or so). The next step was to mod C41 and then add some fullness and reduce the gain some. The mods are basically values used in other Classic Marshall amps and applied to the JVM. However it has it own voice, after the mods it's more than just a Classic Marshall amp, it's more like a hybrid. There's no fizz in the distortion, bass is tight and you get a wide variety of overdrive channels to pick from. Using an Ibanez tube screamer up front to push the amp sounds great!

I suggest modding the bright caps first and see what you think then try modding C41. Then try reducing the compression and gain. One way to lower gain is to use a 5751 or 12AY7 tube in any of the first 3 tube sockets. Experiment by trying the lower gain tube in one of the sockets but test it in all 3 to see what you like.

There are some other mods suggest in the Marshall JVM forum and one that is quite nice is an adjustable Negative feed back knob. Dialed one way the amp is smoother sounding and dialed the other way it's crunchier.