Mesa Nomad 55 Mods Visual Reference

[manicstarseed]

I have owned my Mesa Nomad 55 combo since 2001. As many Nomad owners attest, they can be an exercise (sometimes to futility)  coaxing KILLER tone from these amps. Well this lead me to acquiring my Express
5:25. This made my Nomad... sort of expendable. I stumbled upon some mod threads on The Boogie Board ( http://forum.grailtone.com/viewtopic.php?f=4&t=56044 and http://forum.grailtone.com/viewtopic.php?f=4&t=36317)

I documented my experiences and consolidated the information and  posted the following in its own dedicated thread and wanted to share with my friends here at Strange Design....

Of Particular interest is the stuff on the negative feed back (Mod 3).... defeat or tuning of this makes for some massive tone and wilder amp. My Nomad goes from lion to MONSTER now at the flick of a switch.

Now the post....

After hearing the difference that some of these mods did for my Nomad 55 1x12 Combo, I concur that some of these mods are a must have if one is in anyway dissatisfied with the stock Nomad Tone. I realize that many are not instantly comfortable doing Mesa mods, I wasn't. I figure, having a visual overview of the mods would help people better evaluate their willingness to perform said mod.

All the mods shown are MY interpretations of the mods discussed in these treads:

This is not definitive. I may have missed something. I may have omitted something because the discussion seemed to indicate it was better open way or another.

Please provide comment to correct any issues or clarify the "design" or intent of these mods.

Many thanks to all the people who contributed to this body of knowledge. Many a brave souls are out there pulling and replacing caps before evidence proved it safe. Many smart people thought long and hard while evaluating Nomad and the potential mods. Even more have stuck with the Nomad, not able to realize the full potential of the amp. I do want to acknowledge nomad100hd, Koresh, Tommy_G, shytfayse, jaquetapus, KozMcCharlie, earachemyeye, fretwhizzy, lerxst88, and all the people involved in the original threads for pioneering these mods.

This image is based on my Nomad 55 combo. I am assuming that all the Nomads are laid out in a similar fashion.

I will be filling in the details of the individual mods over the next week.
Nomad MOD Map


1 - FX Loop Capacitance Mod

BEFORE: AFTER

Why?
If you do only one Mod for tone - This is it.
This cap value is reduced from 0.005 uF/5nF/5000pF to roughly 50 pF (my 47 pF cap measured at 50.1), that is 1% of the stock capacitor value.
This capacitor attenuates (to some degree) most frequencies above 100 Hz, Its not the preponderance of bass/lows in the Nomad that makes mud, it  is the absence of highs. This mod gets  you 90% of the way there. See Koreth's  evaluation here: http://forum.grailtone.com/viewtopic.php?f=4&t=36317&start=90 proves that  no other one mod does more for your tone than this one.

Materials:
47 pF, non polarized cap, silver mica or ceramic (stock)

Steps:
-Carefully remove .005uF (5nF) capacitor shown. - Use a low power soldering iron to heat the cap lead near the board while gently pulling on the heated cap lead with a needle-nose. The solder will heat and release the cap will then pull out.
-Prepare the 47 pF cap - Trim off some lead. Give your self more lead than the stock part.
-Using a needle-nose type tool hold the lead of the cap and place it like you would insert it into the holes from the  removed cap.
-Install Cap - Heat New cap lead, close to board. When the lead gets hot enough the solder will melt. Gently push the lead 1/8" into the melted solder and hold. Remove iron, breath and then let go of cap.
- Install Cap - Do it again for the other lead.

Variations:
-Using a capacitor value  greater than 47pF will begin to trail off the high end. 47 pF was selected for the flattest response across the guitar spectrum. If this mod is too bright for you, you can always add a cap in series to add to it. Another 47pF cap in parallel to the one added would yield  a 94pF.This is one reason why you would want a longer cap lead on the replacement cap.
2 - Mud Mod

BEFORE: AFTER

Why?
This was the original Mud Mod that got all this going.
This  has a subtle effect on your tone.  
Reports are that you stand out in the mix better.
If you love the tone and just need to be more present in the mix, this is the mod for you.

Materials:
None

Steps:
-Carefully remove one leg  .120 pf capacitors shown. - Use a low power soldering iron to heat the cap lead near the board while gently pulling on the heated cap lead with a needle-nose. The solder will release and the cap will pull out, one leg at at time.

Variations:
-If you like the mod, clip the cap leads.
3 - NFB Extreme Switch

BEFORE: AFTER


Why?
The Nomad 45 basically has this switch so it applies to 55 and 100 owners only. 45 owners can look to variations for some other ideas.
The extreme switch strips the negative feed back to the PA.
Some  people simply remove the wire from the 8-ohm tap, this mod shows the installation of a toggle switch. This is a Mesa and we love our options, thus the switch.
Without the NFB The amp is very much "alive" and the high end  brought about by the first 2 mods are tempered.

Extreme is a good word for it. The amp gets LOUD and is a monster in this mode.
Glibly speaking, I think this feature is so awesome, this amp is too good for the original price point, this the 45s got it

I run it in both modes so I welcome the switch.

I expect it will wear the tubes out sooner. This has not been confirmed or refuted with statistical evidence.

Materials:
Toggle switch (the one in the pix is rated for 125V)
18ga braided wire.

Steps:




NOTE: you have to watch out for the output transformer when you locate the switch hole. Mine missed as planned but was a little close.  The hole location is up to you, but the stock wire is only so long. Without adding wire, the hole location is limited.


Variations:
Variable NFB defeat using a push-pull 1Mohm pot shown,


4 - Reverb Mod
Note: While I am considering it, I have not performed this mod. This is how I understand the mod to be performed.

BEFORE: AFTER

Why?
Reverb in channels 2 and 3 are weak.
Decreasing the resistance allows more of the  reverb signal to come through

Materials:
(2) 220  kOhm Resistors

Steps:
-Solder a 220 kOhm resister in parallel to the 330 kOhm resistor as shown by shytfayse's image below.


Variations:
There are some Cap replacements but I have not seen anything that I would hang my tone on.

5 - FX Loop Mod - Parallel to Series
Note: While I am considering it, I have not performed this mod. This is how I understand the mod to be performed.

BEFORE: AFTER

Why?
You rather have a series FX loop instead of a parallel loop.
This was one of the first mods discussed. The mix level pot is one other component that the signal simply does not need to go through.

I have seen very little evidence in the discussions where this mod is clearly effective as a "tone mod." There are better places to look for tone. (Mods 1, 2 and 3 above)

I would personally do this because.-  Sans-Nomad reverb, I want reverb last in my loop and that means I need a good dry signal and parallel loops with wet/dry mixes creates complications with a delay that  can kill the dry signal. My setup would match the Express's.

Materials:
None

Steps:
-Pretty straight forward...


Variations:
- Simply remove  wire 1 and connect to  position 2 (1 & 2 connected). Remove and insulate 3.
- Simply jumper solder jumper between  connection 1 and connection 2 (1 & 2 connected). Remove and insulate 3.
- Use a push-pull pot or on off switch to choose parallel or series operation.