Mesa/Boogie TriAxis Phat Mod Reversal



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I’m not what you would call an active member of the forum but since I got most of the information for this mod from here I thought it would be nice to give a little back to all of you. Let me start by saying that this mod is really simple but the Triaxis is not. As a matter of fact it’s a fragile and complex unit. This is why I don’t encourage anyone without previous soldering experience to perform the mod.

The other thing to say would be that you should pay attention while working on any tube device since there may be lethal voltages and all that crap. But if you are confident enough to work on a Triaxis you probably know what you’re doing and if you don’t maybe you shouldn’t be such a cheap bastard and send your unit to Mesa.

Now that we got that out of the way…let’s fire up that soldering iron and start taking out the bazillion screws this thing has Initial information

I’ve seen two pieces of information regarding this mod one is this picture and the other one is a little text saying pretty much the same. I’ve also read that it seems to be some degree of inconsistence between boards so I took this schematic from and opened up my unit. I checked every part of the hand written schematics and it was almost exactly like it was on my Triaxis. The only difference was the order of C12 and R46 but since they are in series it doesn’t matter. So from what I could gather the instructions for the mod make sense.

The mod takes place within the TX4 board which is the one Mesa added specially for LD1 Red and doesn’t alter the other modes in any way.

I can tell my unit is V2 because it shows 2.0 all over the display on startup, the serial number is 62XX and it has MIDI continuous control capabilities.

I can tell is a Fat mod because, aside from sounding like poop on that mode, the factory presets are as follows:

Preset 10: 6.0 6.0 7.0 8.0 2.0 0.0 5.5 2.0 0.0

Preset 11: 6.0 6.5 7.5 7.0 5.5 0.0 4.5 5.0 0.0

I should mention that it’s impossible to get a decent tone from LD1 Red as it is. Yes, it sounds fat, but it’s a loose and undefined kind of low end. So if you find your unit to behave this way on that mode you probably want to get rid of the Fat mod. Sound Differences

Before you even consider performing the mod I would like to state that after I did it to mine it sounded amazingly tight and focused but there is an overall fizz factor that’s hard to tame. I think this is the stuff that made them create the fat mod in the first place. It is the same kind of fizz that you can find on a JCM800 and it’s not that easy to eliminate. Either way I think Mesa’s “solution” was quite poor. I’ve worked on a lot of Marshallesque designs so I know a thing or two about this kind of distortion and there are a couple of improvements I will be trying out in order to make this mode fully controllable but for now let’s focus on undoing the Fat mod. If you still want the original “Recto” sound keep reading. My opinion is that it is way more usable than the Fat mod but you may differ. Mod Details

The mod can be separated in three parts, the first one changes the filtering between the first and second gain stages. The second one alters the tone stack section and the third one change the effect of the mid and bass EQ settings.

Since the unit is crammed inside and the TX4 Board is really close to the top cover you should make sure the new caps don’t stand up too tall. There’s no need for measuring, just compare their height with the existing components. That alone will ensure proper clearance.

These are a couple of pictures of my unit’s TX4 board as it was when stock.

Looking at the first picture, locate the three places where the mod is done. Part one is on the top left corner of the board. Part two is on the top right corner and Part three right in the center of the board. PART ONE Replace R45 with 330k Replace C22 with 47p R46 = 82k C12 = 1n The following schematic shows the difference between my unit and the Recto version. These pictures show the steps… PART TWO Replace R9 with 120k Replace C6 with 1n C5 = 1n R44 = 33k C6 was 1n on mine but that’s not the case with all the units. I removed it anyway to show where it is.

Difference between my unit and the Recto version. Steps…

Notice I used a 3k3 resistor for R44 instead of the correct 33k value. The original value is 33k.

PART THREE Replace R33 with 1M Replace R34 with 10k Just two pictures for this one…


I was going to make before and after sound bites but I got carried away and forgot to record the before one…sorry guys

Hope this info helps Last edited by Inkomodo.Dragon on Tue Oct 01, 2019 10:23 pm, edited 3 times in total. Top