Building a preamp..

[MarshallMesaUser]

Can anyone help me iscolate what pieces of the mark 3 circuit to build a preamp version of the LEAD only. If someone would be kind enough to draw me a schematic would be greatly appreciated! :

But any general help/info will also be appreciated.

[legendre]

Take a look at this semi-legible schematic image:

http://www.tubefreak.com/mk3-1.gif

Bottom center of image - "Lead circuit"

-L

[chipaudette]

Hi,

The Mesa Boogie schematics that are out there are really poor quality scans. For example, the link by legendre above is a bit tough to read. It can be hard to see the component values. So, I'd recommend following the Mk III schematic for the overall layout and then look at the Mk IV schematic for actual values. The biggest difference between the two amps is that the MK IV has two different tone stacks...one for lead and one for clean. It just switches between the two. Otherwise, the schematics are very similar...

http://www.schematicheaven.com/boogi...oogie_mkiv.pdf

Also, I've modified my amp to have much of the MK IV as my pre-amp (except I only have one tone stack). Note that you're not going to get what you want if you just recreate the "Lead Stages" on page 2. Nope.

One key is that you need V1A->ToneStack->V1B before the "Lead Stages". These pre-distortion tone controls are a key part of the sound.

The 2nd key part is to follow the schematic in how the "Lead Stages" come back into the circuit. Notice that it returns to the circuit just before V2A. Notice also that the regular (non lead) signal path joins here, too, after passing through C2 and R102. This parallel path is important...I believe that it really affects the sound. Others may disagree, but there is a reason that this parallel path survived in four iterations of the Mark series amps throughout the entire 30 years of its production.

Finally, do not omit V2A. The returning lead signal (and the parallel clean signal) both slam this tube pretty good. It distorts. If you omit it from your design, you're going to miss another important portion of the overdrive sound.

In case you're counting, the Mesa MK overdrive sound requires 5 tube stages. Since there are two tube stages per actual tube, you'll need two and a half 12AX7s to complete your pre-amp.

Good luck!

Chip

[alien]

Hey Chip

If your still there..do you have any further info on this like newer schems or layouts--man I love the Mark iv sound and you just cant get it off the Dual recto. The new mark 4 reissue seems to be one of the best amps(for this sound) I have heard in years.

[chipaudette]

No, I don't really have any new info. The schematics out there are still the same.

As for new schematics, I don't know how long it'll take before the schematic for the new Mark V (introduced at NAMM last week) makes it out into the public.

I'm very curious though.

Chip

[alien]

Hey thanks