[Tube Pre-amp project] The JCM800

[bancika]

I must agree with that. My Tube reactor has very similar topology to JCM800 preamp so results should be similar. First I got marshall DFX (solid state) and distortion really sucked. Then I build tube preamp and put it in from of clean channel (which is decent by itself) and still it added some ugly harshness and coldness to the tone. When I finally built very clean fender princeton 5f2-a clone (all tube, of course) my tube reactor showed what it can do. It sounds the best like that.
So you'll definitely improve over solid state but for full effect expect to build some tube poweramp or cleanish tube amp soon
Cheers

[runmikeyrun]

i'm sorry if i meant that it wouldn't be a good build, that's not the case!  We used the DI from his amp into a Kustom pa head and 2x12 for a guitar amp monitor for the drummer for a while and it sounded pretty good.  It's all in the tubes- for current production the JJs sound the best i think- lots of balance, good low end w/o mud and good top end without being harsh.  So save yourself a step and make sure you have good tubes to start with.

the 900s have clipping diodes IIRC.  800s that i know do not.  I hate the sound of those 900s- they sound compressed, quieter, and buzzy, just like clipping diodes!

[bancika]

I'm not sure about all JCM800 (there are probably more submodels) but famous 1959 Super Lead doesn't have diodes. It's the same preamp like this...
And yeah, diode based marshalls do sound harsh. I've tried JCM2000 and it's not great, JSX was way better 

[MetalGuy]

Did I read somewhere that there was diode clipping in one of the JCM amps?

Yes, there's such an amp made in limited quantity and it's model number is 2205. It has a bridge rectifier in the signal path as seen from the schematic which by itself not very common:

http://www.drtube.com/schematics/marshall/2205prem.gif

I recently built one for a friend who was after Michael Schenker's sound and the sound was specific but not bad.

[bancika]

you men rectifier diodes, not a bridge rectifier...