nomad mods

[Koreth]

From what I can tell those caps that you removed were the cheap ceramic kind. Could one not replace them with a higher grade capacitor of the same (or since we're trying to reduce mud (in other words, trimming bass?)) or lower value and get a similar effect?

If this mod works, and works well, great! However, I cannot help but think that Mesa decided to put those caps of that particular value there for a reason, and quite possibly a very good one. Just what is being affected by removing those capacitors. Removing them doesn't place the PI at risk of oscillating somewhere in it's circuit, wearing/burning out PI or power tubes more frequently, or reducing headroom, does it?

 

[nomad100hd]

Those caps do nothing but dump treble and upper mids to ground. Why did Mesa put them there idk so far no negative side affect but a very much needed positive impact on tone. If you compare the nomad's power amp to other amps power amps you wont find much difference if any. So if those caps r needed it would be cuz of a bad layout.

 

[jaquetapus]

Well, I just did both those mods, and I'm not noticing a huge difference in the bottom end. [Haven't gotten it up to band levels yet tho, that might be the difference. So far just rockin it in my shop.] More comments after I put it through its paces.

-dave

And I forgot my camera while I had it all apart. Sorry.

 

[nomad100hd]

well it doesn't change the bottom in it takes away the mud. basically the PI ha a crossover on it to dump all highs to ground.

 

[nomad100hd]

decrease the highs it makes it sound like a bass boost. Everyone at band practice even the chick singer noticed right away the difference.

 

[KozMcCharlie]

Any ideas as to how the PI mod might work in a 45?

My uneducated guess is that more highs and upper mids means more chime and ring from the EL84s but maybe too much or maybe in a harsh way... I suppose that it wouldn't take too much to try it and see, but maybe someone else can confirm...

Also, are these caps present in any other Mesas?

 

[nomad100hd]

some amps do just have to look at the schematics. i just lifted one leg of the caps so you don't even have to completely remove them.

 

[KozMcCharlie]

OK... I just did the mod on my Nomad 45 2x12 and the result is great for me. The difference is that the sounds more lively and open. On the drive channels it adds chime and evens out the frequency response across the spectrum so that there isn't a huge woolly preponderance of bass and low mids especially on the CH 3. The clean channel has really gotten better in a Blackface sort of way. Cleaning up the mud is a good way to put it, but there's a bit more to the modded sound than that.

As mentioned all that I did was desolder one leg of the cap and bend it out of the way. Easy and very reversible. I can't say how it works with the other tubes, but for the EL84s it makes the amp sound a lot more like a stereotypical EL84 amp...

Thanks for the mod Nomad100!

 

[nomad100hd]

really did turn an okay amp into a great amp for me.

 

[lerxst88]

ill do this as soon as possible! anyone still need pics? PM with what you wanna see!

also what does PI stand for?

any other mods guys? hopefully i might clone a dual recto preamp onto channel three on my nomad so ill take pics of that!

 

[nomad100hd]

i'd like virgin nomad inside pics, mostly for wire routing. PI stands for phase inverter. lets see a dual rec has 4 gain stages and a cathode follower stage. the nomad 3 gain stages and a cathode follower stage in it's distortion channels. channel 2 and 3 share gain stages so if u wanted to alter channel 3 it will also alter channel 2. So unless u rip out the guts of ur amp and do a redesign ur not going to get a recto channel out of 3.

 

[nomad100hd]

also sorry i've not gotten a chance to document the other mods, my X wife decided she can't handle our 3 yr old son so i have him full time now

 

[Tommy_G]

Well....I really do hate turning my amps into custom jobs, but this seems pretty reversible.

I'm going to do a hail Mary and go for it !

I just have to say that what the Nomad brings to the table is the Mk series tone of Channel 2, and a marshally tone of Channel 3, and of course the 'standard' mesa clean tone. It really works for me as a gigging amp. I love it. But yes, there is some mud, and as mentioned earlier, when you use an outboard Pre with this power amp, you immediately know something is F'cked up.

Thanks for posting the schematic change!

 

[Tommy_G]

OK, before I go farther, just want to know if you guys who have done the mod typically use "modern" or "vintage" setting on Ch3 ?

 

[nomad100hd]

modern setting

 

[jaquetapus]

I usually use vintage.

 

[nomad100hd]

ha ha ok so one of each! i do play with my gain up on channel 3. The amp rocks vintage and metal!

 

[Tommy_G]

I looked through a bunch of schematics. The most highly regarded mesa amps (Dual Rec, Mk IV, Lonestar, Maverick) do not have that capacitor/resistor pair that is being recommended to be clipped out of the circuit.

Of interest is that both the Heartbreaker and the Nomad do have these pairs. Note that the Heartbreaker is always complained of as being 'dark'. This same mod will probably be good mod for that amp, too.

One further question: many of the power amps (Mk IV, lonestar, Heartbreaker) have a 0.1 uF capacitor going into the grid of the power tubes, presume this is a bass attenuation? The nomad and dual rec have only a 0.047 uF capacitor. What is the impact of this capacitor sizing on the tone ? I will say that the Heartbreaker always seems to have a much wider girth to the tone compared to the nomad & wonder if this cap isn't part of the reason.

Comments?

 

[nomad100hd]

the .1uf cap will let more bass threw than a .0047uf cap. If i were to change that capacitor it would be to make it smaller not bigger giving the amp more focus/cut. I think the .0047uf cap bass cut is at 154hrz.

 

[earachemyeye]

Ok, I did the cap clip mod on my Nomad 55. The change is subtle but noticable. It's getting late, I can't turn it up to a decent level with out provoking my wife to rage and I want to be detailed in my tone report so I'm going to post tommorow with the full results. So far though at bedroom levels I think I like what I hear.

Joe