mojo 18 watt marshall build

JoeCon · Post by **JoeCon** » Fri Feb 22, 2013 12:34 pm

Guys,

Would you use the same values for a 2 EL84 rocket build?
Or does that need the 250K pots with 2M2 resistors?

Thanks...

M Fowler · Post by **M Fowler** » Fri Feb 22, 2013 3:44 pm

The type 1 with dual 1m pot doesn't replace the 2 x 220k's on the board like the type your talking about Joe. In your version the 250k dual pot is replacing both 220k's on the tone board.

But the previous version I posted for the 18w PPIMV does have the 220k/220k bias resistors removed, so it get's confusing.

Mark

JoeCon · Post by **JoeCon** » Fri Feb 22, 2013 7:22 pm

OK

So the 250K dual pot and the 2M2 resistors take the place of the resistors on the board only now they can be varied thus reducing volume, yes!

Wow plenty of options and variables.

Maybe first time out it's better to say, "Master volume? I don't need no stinking master volume." LOL...

Thanks, Mark.

JoeCon · Post by **JoeCon** » Fri Feb 22, 2013 7:24 pm

Mark

How does this PPIMV compare the the so called "watts" control?
I saw them used on some amps here awhile back but it seems to have lost favor to the LarMar version.

Reeltarded · Post by **Reeltarded** » Fri Feb 22, 2013 7:37 pm

PPIMV is an inexpensive and simple way to control an amp without NFB. Easy, and sounds just about the same at any setting.. barring the physical interaction of the instrument with the amp's volume of course.

So simple even caveman do it. Uhhng!

Work obvious NFB to just not sound good! MAHH!

Ugg

PS: Mikey! ^^^^ Type 2 is for you I do b'leeve.

M Fowler · Post by **M Fowler** » Sat Feb 23, 2013 12:54 am

I have gotton the prime control, or watt's control to work well in an octal Reverb Rocket amp but I think it would be better to use it in conjunction with a PPIMV not alone.

Mark

ampmike · Post by **ampmike** » Fri Jun 07, 2013 5:10 pm

Hey guys,I have got to finish these mas vol in the 18 watt I believe we figured type 2 from Marks posting correct? Which would the Liverpool get?Thanks,I just want to fix and finish all my builds and just play gee tar for a bit,I have the dual pots and resisters now,Mikey

JoeCon · Post by **JoeCon** » Fri Jun 07, 2013 5:50 pm

Mikey

Yes the dual 250K pots with 2.2m resistor will work for the Liverpool too. You're removing the 220K from the board and the pots are taking their place.

But as Miles said with NFB in the Livepool, and not in the Rocket, as you turn the PPIMV down it will effect the NFB. I think Miles and Mark can fill us in on what happens then!!

HTH...

JazzGuitarGimp · Post by **JazzGuitarGimp** » Fri Jun 07, 2013 6:00 pm

JoeCon wrote:Mikey

Yes the dual 250K pots with 2.2m resistor will work for the Liverpool too. You're removing the 220K from the board and the pots are taking their place.

But as Miles said with NFB in the Livepool, and not in the Rocket, as you turn the PPIMV down it will effect the NFB. I think Miles and Mark can fill us in on what happens then!!

HTH...

I'd be curious to know about this as well. Is the result (on a NFB amp) so bad that's it's not even worth considering? I imagine the more NFB the amp has, the worse the Lar-Mar MVsounds?

Bob Simpson · Post by **Bob Simpson** » Sun Jun 09, 2013 4:08 am

I'd like to know as well..

Which MV for NFB, and which for no NFB?

Bob Simpson

martin manning · Post by **martin manning** » Sun Jun 09, 2013 5:10 pm

If you reduce the signal after the PI (Lar-Mar PPIMV, e.g.), then the GNFB signal is reduced relative to the signal at the point where it is returned, at the PI. The NFB and the effect of the presence are both diminished as the MV is lowered (for the typical LTPI and presence circuit). Pre-PI MV, a la Marshall "Master" circuits, does not disturb the NFB and presence. Lar-Mar PPIMV still works very well with GNFB, however. There are a bunch of Plexi owners that are very happy with it.

Lindz · Post by **Lindz** » Mon Jun 10, 2013 8:04 pm

I seem to recall reading somewhere about people using variable negative feedback using a pot or switch to offset this somewhat..

anyone try that and have any tips..?

sepulchre · Post by **sepulchre** » Tue Jun 11, 2013 4:42 am

martin manning wrote: There are a bunch of Plexi owners that are very happy with it.

What I built is not exactly a Plexi but has a High/Low switch to get pretty close to a Plexi sound in the Low mode. I put a PPIMV in it and I'm no expert but I think it sounds Great. Yes, there is a difference with the PPIMV turned down but it's not horrible. In fact I've put it to good use in recordings. That said, it does sound better with it dimed and I generally don't turn the PPIMV down past about half, but that's fine around our house.

Sazafraz · Post by **Sazafraz** » Sun Jun 16, 2013 3:09 pm

This a cahode biased amp so you might you consider something like a VRM as it allows you to turn the volume down and not loose the power amp distortion. The bonus side is some power amp compression

mark enger · Post by **mark enger** » Sun Jun 16, 2013 9:35 pm

A big part of the 18watt sound is no NFB, add if you want but build with a disconnect, I have not had a lot of luck with vvr because most or all of this amps mojo comes from cranking the amp up, and while using a full tone stack is cool it does suck some tone from the amp as does a MV, The ceriatone layout has always been my go to design for a TMB its very bassy and ballsy and most complaints with this amp is top-end sizzle or fuzz, that being said which is just IMO, its hard to beat a well built liteIIB with some mullards mark

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mojo 18 watt marshall build

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