Nomad 55 mud mod

[the recluse]

I'm actually taking my Nomad 100 combo over to my amp tech this afternoon to have the mods from the Visual reference thread done: Cap swap in the effects loop, lift the 120pf caps, and add resistors on the reverb. I'm also going to swap out the 25K effects loop pot for a 50K dpdt push pull pot with a 50K resistor across the terminals. That way I can switch the loop form series to parallel and still have the blend knob. I'm also going to have him lift the negative feedback tap and replace the reverb pot closest to it with a 100K push/pull DPDT pot so I can switch the feedback loop in or out. I may even go ahead and have him throw a new set of tubes in too. We'll see.

I'm really looking forward to hearing what this will do to the Nomad overall, and I like the idea of having the loop and NFB switchable without having to drill out the chassis.

 

[Mordacain]

I'm actually taking my Nomad 100 combo over to my amp tech this afternoon to have the mods from the Visual reference thread done: Cap swap in the effects loop, lift the 120pf caps, and add resistors on the reverb. I'm also going to swap out the 25K effects loop pot for a 50K dpdt push pull pot with a 50K resistor across the terminals. That way I can switch the loop form series to parallel and still have the blend knob. I'm also going to have him lift the negative feedback tap and replace the reverb pot closest to it with a 100K push/pull DPDT pot so I can switch the feedback loop in or out. I may even go ahead and have him throw a new set of tubes in too. We'll see.

I'm really looking forward to hearing what this will do to the Nomad overall, and I like the idea of having the loop and NFB switchable without having to drill out the chassis.

I think you'll be happy with it. I'm considering reverting my Nomad 45 back to pre-mud mod specs but to be honest, the clean channel really does sound better (just my drive channels are too bright for my taste now). The 55 and 100 definitely seem to benefit more from this mod from everything I've read. Good luck with it!

 

[Tommy_G]

I'm also going to have him lift the negative feedback tap and replace the reverb pot closest to it with a 100K push/pull DPDT pot so I can switch the feedback loop in or out. I may even go ahead and have him throw a new set of tubes in too. We'll see.

I'm really looking forward to hearing what this will do to the Nomad overall, and I like the idea of having the loop and NFB switchable without having to drill out the chassis.

Take the Single Rectifier (Solo50 or Rectoverb) schematic(s) with you.

The reason I suggest having your tech look at the Single Rectifier Schematics is this: The voicing on Channel 3 on the Nomad is 90% the same as on the Lead channel of the SR !!! Most differences due to the increased impedance coming out of the (better) paralleled V1A+B of the Nomad, and how the vintage/modern settings are handled (Nomad in the preamp, SR in the NFB loop).

There is both a v.1 and a v.2 version of the SR. The v.1 had a vintage/modern switch on the lead channel, most like the Nomad. However, v.2 added a third pole to the switch, making it "raw/vintage/modern", with the raw setting more in the range of blues tones...I envy THAT!

WOW. Who would have thought you could have possibly the best clean/pushed channel Mesa ever made, but a SR on board as Ch3 !!!...not to mention the Nomad's Ch2 - which is an improvement over the Heartbreakers Lust Lead Channel and voiced like the British version of the Mk2 series lead channel! ! ! .

However, the SR appears to have a far superior NFB configuration than the Nomad, and it doesn't look like it would take a rocket scientist to mod the Nomad to SR specs. An easy low intrusive approach would reconfigure the NFB switching with manual, rather than automatic switching, essentially making it a really flexible home and recording amp.

With greater PCB intrusiveness (and mod skills), it may be possible to re-purpose the "vintage/modern" switchable relays (and switches) on the lead channels to control the NFB pathways, rather than simply bumping up the signal hitting the PI as it does in the Nomad...which of course, comes back in NFB, whereas the SR bumps up the signal level in the PI via reducing NFB.

I have researched this as much as I care to, but *THIS* is what I believe to be the ultimate answer to the Nomad 55/100 tone woes. The Nomad must carry the SR configurable NFB design.

Incidently, a disconnected NFB loop is one of three positions in the SR's NFB loop, I believe associated with the "Modern mode" setting of the v.2's lead channel....and auto-switching Rhythm channel NFB includes a 25 k potentiometer. And a much more conventional NFB loop for the other lead voicings of the SR Lead channel.

Basically a wishlist of everything we've talked about for months on this and other threads.

Once the Boogie Board gets done with the Nomad, it will be the most flexible and best sounding modern amp Boogie has made.

Please let me know if you are able to do this?

 

[Koreth]

I fail to see how the Red channel of the Nomad is similar to the LD channel of a single Recto. The gain structure in the Nomad goes 1st gain stage -> gain control -> 2nd gain stage, 3rd gain stage, DC-coupled cathode follower -> tone stack. The LD channel of a single recto goes 1st gain stage -> gain control -> 2nd gain stage -> 3rd gain stage, 4th gain stage, DC-coupled cathode follower -> tone stack. The bias and cathode feedback bypass arrangements are different as well. Nomad: center biased, -> center biased -> warm biased, all of em bypassed with 1µf capacitors for about full gain down to 120Hz, with the exception of the 3rd stage. The 3rd stage still has the 1µF bypass cap, but with a 1k? resistor in series with it, reducing the bypass effect, and the amount of gain boost above 120Hz at the 3rd stage. By comparison, all of the Recto's gain stages are biased slightly cool-ish of center with 1.8k? resistors, and again bypassed down to 120Hz with a 1µF cap, with the exception of the 3rd stage, which is biased icy cold just above cutoff with a 39k? resistor and has almost no gain with that large of a cathode resistor and no bypass cap. The Recto with its one gain stage biased icy cold near cutoff is going to have much more distortion than the Nomad.

I'm certain I've posted such before, but comparing schematics, the Nomad's red channel strikes me as more similar to a hot-rodded Marshall 2203 circuit, and the orange channel more similar to a one-wire-mod Marshall 1959, than either is to a Recto or Mk2 lead.

 

[Tommy_G]

I was looking at the Solo50 schematic on schematic heaven. Pretty sure that the v.1 version.

Thanks for your input.

My post referring to voicing not gain structure. At 1000% gain the signal is nothing more than a slightly tweeked square wave, and the Nomad has 8000% and the SR, 10000%, so the gain structure itself isn't isn't going to deliver a big different in voicing. Maybe 10% at best.

Which leaves us with the tone stack and the NFB voicing to shape this god awful permanent unexpressive squarewave into some other kind of mush. You may wish to look at the common ground, or potential common ground on those items.

You are seeing the differences, I'm looking at the similarities. I'm pretty sure Mesa even advertised that the Nomad Ch3 was a "Rectifier"-ish channel, as part of the whole "Nomad" wandering schtick.

Which brings me to my wish list. A variable presence control on Ch1, and a configurable NFB loop with a structure that makes more sense to educated guitar technicians than "that NFB loop is VERY unusual".

The Nomad manual talks about the presence being controlled in the NFB loop, but the schematic doesn't back it up. Everything points to shortcuts and/or marketing decisions made as the Nomad got delivered from design to production.

I am convinced that there was more intended for this amp than meets the eye, and I believe the SR offered up some clues.

 

[the recluse]

Just got my Nomad 100 back from my tech and this is what I can report so far.

The FX loop brightness mod (swapping the 5uf for a 47pf) is a winner. Overall the amp is much brighter and seems airier to my ears.

I suspect the mud mod (pulling the 120pf caps) is contributing to this as well, since I had that done too.

The FX loop series to parallel with push/pull pot to switch is a winner. Currently set in series as default and can be pull out to get back to stock function.

NFB mod is a BIG winner. I also had this made switchable with a push/pull on the CH3 reverb pot. THis is like night and day. Switch back to stock mode sounds like throwing a blanket over the amp. It's much more alive and responsive and I am really happy to have done this.

Reverb mod is ??? My tech did the mod, and as we were testing before final assembly there was still barely any reverb coming through on channels 2 and 3. Channel one can get all kinds of fendery, but there's barely anything on the orange and red. We pulled the extra resistors to compare and just left them out. THere really wasn't much going on before or after the mod, and since I barely use the reverb on those channels I figured we might as well leave them stock. I plan on researching the other threads about this and maybe going back in at another time.

Haven;t had a chance to play this in a band setting yet, but I'm looking forward to it. A LOT.

 

[Tommy_G]

I really like your use of the push pots to switch these mods in and out!

 

[Tommy_G]

Reserved for future use. :mrgreen:

 

[the recluse]

I really like your use of the push pots to switch these mods in and out!

Thanks!

It seemed like a good way to go to retain the stock operation without having to drill out the chassis. The Reverb pot is a 100KB so it seemed like a no brainer to stick the DPDT pot in and use the switch for an unrelated function.

The FX pot was a little trickier because we couldn't track down a 25KB/DPDT pot with solder lugs so we shunted the pot terminals of a 50KB/DPDT with 22K resistors to approximate the value of the 25K pot.

FWIW, and I hadn't seen this listed in any of the other threads, these were 16mm Alpha solid shaft pots and they fit perfectly. The knobs were a little stiff to get on but they did fit.

 

[NomadExpress]

Just got my Nomad 100 back from my tech and this is what I can report so far.
...
Reverb mod is ??? My tech did the mod, and as we were testing before final assembly there was still barely any reverb coming through on channels 2 and 3. Channel one can get all kinds of fendery, but there's barely anything on the orange and red. We pulled the extra resistors to compare and just left them out. THere really wasn't much going on before or after the mod, and since I barely use the reverb on those channels I figured we might as well leave them stock. I plan on researching the other threads about this and maybe going back in at another time.
...

Thank you for reporting out back the reverb mod. I have been considering the mod and was wondering....
I will look into the hink there is a cap swap mentioned but I also recall that the results were less than stellar.
I will look deeper and see if I need to change original nomad mod thread. I will then update the Visual Reference.

 

[Tommy_G]

All my Mesa's came with green power tubes.

I stuck a pair of Yellow 6L6's in the Nomad 100 today and ran it on half power, and Ch2 almost came to life. It was 110 db (approx.) but at least not 150 db when it hit paydirt. If I got it down to 100 db, I'd be set.

I was able to turn the preamp gain down to about 10:00 (where it should be for a nice Marshally crunch), and I got enough articulation to make it pass the crunch test.

YAHOO!

Now, what to do with Ch3 ? Now that I got crunch on Ch2 rather than gain, I used Ch3 as the OTT gain tone, rather than the crunch tone. It even sounded better than usual because of the power tube switch.

This is definately a better use of the amp, but Ch3 still needs work.

Anybody got a pair of 6L6 Red's kicking around to compare against the Greens or Yellows?

It appears that what I'm discovering is that Mesa's fixed bias program keeps non-techies busy with a lifetime of fiddling around trying to find something that a simple bias adjustment may well have solved.

 

[earachemyeye]

Did the NFB mod on mine today using a mini toggle switch. As previous poster said this is a big improvement. I also hear the blanket effect switching it back and forth. My other observations are:
1. The amp is loud as hell now
2. It's way more dynamic and touch responsive.
3. The bass gets woofy and boomy at previous settings. Gotta dial it back but there's more low end there.
4. More preamp gain on tap. Had to dial the gain down from previous settings but the channels sound better than before at less gain and worse than before with large amounts of gain. The breakup is nastier with more lows in it.
5. The amp cleans up better with the volume knob. The "body" of the tone remains, it doesn't thin out so much as before.
6. Channel 3 really shines now for that chimey Vox like sound. Before if I set the gain real low it became stupidly thin and turning up the channel volume did nothing to help. Now I can set the gain way down and turn the channel volume up and WOW. Clarity, chime and TONE.
This mod is a winner but it makes the amp harder to tame for the volume. Half power mod anyone? Someone had mentioned using a pot to vary the amount of NFB. Is this possible? A big THANKYOU to all the gurus who have been so kind to share your work on this amp. We're getting closer to having our own custom boogie model!

 

[Tommy_G]

Thanks for more detailed review above. Details are far more helpful than one-word opinions to be sure.

Guitar tone has a lexicon all its own, and I haven't got on to all of it yet....So, Question:

Is "nastier" a good thing or a bad thing?

 

[earachemyeye]

For me it's a negative. The added bass and blanket being lifted make for a fuzz/fizz sounding breakup at higher gain settings which I'm not fond of all the time. Since I don't use alot of preamp distortion and the amp now sounds better at low gain settings, the tradeoff works for me. For more saturated sounds I throw a pedal in front. YMMV. Thanks for asking. I'd also like to add one more thing after playing around with it for awhile. Ch.1 pushed is incredible now. I've never liked that setting, I always thought it to be to harsh, thin and boxy for my tastes. Now it is thick crunchy lead tone goodness.

 

[earachemyeye]

I did some research about adding a pot to vary the NFB. I learned that in most amps there are 2 resistors in series that set the amount of signal that gets fedback into the PI. One is a shunt to ground and the other is the one to replace with a pot so this is for sure possible. Without a schematic I'm dead in the water. Where did you all find the schematic? I'd really like to try this. Thanks in advance.

 

[Tommy_G]

google 'schematic heaven', only the webphix link woriks, scroll down and find & click "Mesa Boogie", then Nomad

 

[earachemyeye]

Got the schematic. Thanks. Pretty sure I found the right resistor and have a pot to insert. The plan is to put the pot in series with the original resistor so that I can dial up the resistance to add less -feedback or dial it back down to stock spec or anywhere in between. There is a thread on the Marshall forum (a great read on this subject) where they are doing this mod to the JVM model with great results. If I've got the right resistor (39k) off the 8ohm tap it would be alot of -feedback hitting the PI in stock form. Should be done tomorrow, I'll report back.

 

[timgman]

Certainly Interested in the resilts.. video?
!!

 

[earachemyeye]

Finished... and it works! Sorry I don't have a video cam. Took some pics to post up on the visual reference thread. I'll try doing that this weekend (never posted pics here before). I didn't get to play with it too much tonight but my initial impression is that it does what I was hoping to do-find a balance of less NFB and volume. I'll have some time tomorrow with no wife or kids in the house to mess with it some more to give a more detailed report.

 

[Tommy_G]

If you can, find the best setting for on stage volumes, then measure the resistance. I wouldn't mind knowing how far out of whack the feedback is.