MARSHALL JMP-1 Tube Question

[Fret-Shredder]

Hey guys that know about this preamp... I picked this JMP-1 up locally for a really good deal and when I opened it up to have a look inside there are 2 of these GT 12AX7s inside. They sound ok to me but I would like a little more GAIN if possible. Im not sure how much the preamp actually uses the 12AX7s for the gain. If the 12AX7s do matter for the gain structure with this preamp can someone recommend a tube that I will notice a gain boost compared to this GT. Thanks in advance.

I have these 12AX7s on hand that I have never used. Are any of these higher gain and a better tube than the GTs? The other thing I dont know is which tube in the JMP-1 is for the OD channels and which one is for the CLEAN? I did a Google search and could not find any info on that.

 

[rickenbacker198]

I don’t remember which side is which...
Pull a tube you’ll find out

On the gain side.
I liked either a ,
NOS EI Yugoslav 12ax7 or
Standard Chinese 12ax7c
The Chinese one had the most perceived gain.
EI tube has a nice grind to it.

On the clean Sovtek 12ax7LPS.

 

[shredhead7]

Having owned many preamps over the years, I owned the JMP1 for awhile as well, the tubes don't make that much of a difference. You can hear some subtleties, but mostly I tried to find some that weren't crackling after a few hours. Something that I didn't pick up on until much later is, don't be afraid to boost the preamp. It's essentially the preamp section of 900 with midi features, so slap a sd-1 or ts in front of it.

 

[PeteLaramee]

I liked chinese tubes when I had my Jmp-1.

 

[Little B]

When you run the jmp-1 into a really good poweramp such as a vht 2150,classic,or Marshall 100/100,or any others of that calibur,you can certainly hear some difference with better tubes in it.Less noticeable with lesser poweramps in my experiences.Its been a while,but i believe i put a groove tubes gold and EH in it and it did add a touch of gain and took away some of solid stateness of it..Its a fairly cheap investment too!

 

[JMP2203]

that gt is actually a JJ, so try the tung sol and the penta(probably a C9) and see which one you like,

and on the jmp1 when you take one tube off the unit the OD channel or clean channel will mute, no sound, so that way you can know which one afect each channel

 

[Price]

When Voodoo mods JMP1's they put electro harmonix tubes in the gain channel. The gainiest tubes are the newest tubes, and maybe a rather bright tube as Marshalls have that upper mid focus. I think the suggestion to try Chinese (Ruby, TAD) is sound. GT also sells a Chinese tube as the GT12AX7C.

I have tried a few Ruby 12AX7AC5 HG+, and although I can't say they are gainier or more powerful, they do seem to have a more aggressive, in-your-face character in my JCM 800 2204.