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Nomad 55 mud mod
- Thread starter rolue
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earachemyeye
Well-known member
Took the amp to practice last night and I like it. I just wrote a detailed review and timed out or something because it woudn't post. ARGGGH! In short, it does what the extreme switch does but to a lesser degree. I don't have a photobucket account so I can't post pics either. All you have to do is locate the 39k resistor on the schemo in the NFB loop (it's the first one) and replace it with a 500k linear taper pot and a 270k resistor. Run 2 wires from where the resistor was to the pot. One with the 270k resistor to the middle lug and the other to an outside lug then connect the empty outside lug to the middle lug. This gives you a range of 0-177k. Probably don't want to go all the way to 0 so I marked where 39k was in the rotation on my amp. I put the pot where ch.3 reverb was on the back to retain a stock look. I use an outboard verb unit.
earachemyeye
Well-known member
For gain tones I like it all the way up (177k). For cleans all the way down, even a little lower (33k?). I still have the mini switch in there so I'm thinking about using that to switch the pot in and out if it bugs me too much. All the way up and ch.1 switched to pushed is really nice now. Also the tone controls work differently with less NFB (as I posted before). I suspect it has something to do with the r/c circuit that follows the 39k.
earachemyeye
Well-known member
Not anymore than before however there is a touch more volume and gain at lower settings. I don't mind this because it punches through better since the amp is more responsive. I'd be happy to send the pics to someone who can post them on the visual reference thread.
NomadExpress
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i can do it. send me a pm with your e-mail.
Everyone,
Often read the boards here but rarely post. Had a thought on the Nomad. I personally have a 55. One area no one seems to focus on is the cabinet. If you are a blues fan meaning fender cleans then the open back makes sense which benefits channel one but I find the bass in channel two and three to be too loose. I added an additional piece to the back to mimick the 3/4 open cab design Mesa throws on the Rectoverb, Heartbreaker, and even the 2x12 Nomad 100. I was pleasantly surprised by how it tightened up the bass and to me really improved hi-gain sounds on the amp. Total cost was free since I prototyped with a scrap of 3/4 plywood.
I am still trying to work on the clean channel because that loose bottom end was rather nice but I love the improvement to the other channels. I know Mesa tunes the panel with a rectangular cutout centered on the speaker cone so I may go further down this route and make an entirely new back panel to make a factory-like solution.
Give it a try. All I did was remove the piece of metal channel that protects the tubes and reused the two screw holes to attach the new piece. The top of the board looks exactly like every other Mesa 3/4 panel and then I cut out a 2"x12" notch centered on the bottom which mimicks a port when stacked on top of the factory half panel. I think more time is needed to better understand the Mesa C90 and design a better port size and placement but I think this is rather promising.
Often read the boards here but rarely post. Had a thought on the Nomad. I personally have a 55. One area no one seems to focus on is the cabinet. If you are a blues fan meaning fender cleans then the open back makes sense which benefits channel one but I find the bass in channel two and three to be too loose. I added an additional piece to the back to mimick the 3/4 open cab design Mesa throws on the Rectoverb, Heartbreaker, and even the 2x12 Nomad 100. I was pleasantly surprised by how it tightened up the bass and to me really improved hi-gain sounds on the amp. Total cost was free since I prototyped with a scrap of 3/4 plywood.
I am still trying to work on the clean channel because that loose bottom end was rather nice but I love the improvement to the other channels. I know Mesa tunes the panel with a rectangular cutout centered on the speaker cone so I may go further down this route and make an entirely new back panel to make a factory-like solution.
Give it a try. All I did was remove the piece of metal channel that protects the tubes and reused the two screw holes to attach the new piece. The top of the board looks exactly like every other Mesa 3/4 panel and then I cut out a 2"x12" notch centered on the bottom which mimicks a port when stacked on top of the factory half panel. I think more time is needed to better understand the Mesa C90 and design a better port size and placement but I think this is rather promising.
You raise a good point.
When I demo'd and instantly purchased my nomad 100 head, I could swear it was hooked into a Recto 2x12 with v30's.
Got it home, and poof.....nfg with my 1x12 open back C90 lonestar cab.
That said, it isn't only the speaker. Lifting the NFB is a design feature of a lot of modern boogie high gain amps. Also, that R/C network after the feedback resistor revoices the amp so that it doesn't have the sonic footprint that other amps like the Heartbreaker have.
I'm working out a mod for Ch3 that will surefire be a major optional improvement.
The good thing about a marginal amp is that it stimulates an awful lot of education...It's actually a pretty decent 2 out of 3 channel amp between the clean and ch2. The lot of us will be employable as amp techs by the time we're finished with it. The similarly notorious Formula Pre went through some significant modding research, and by the time it was done, the lead channels were pretty asskicking. There's something special about it's ch3 now that I bet an amp company couldn't design for. Just a lucky accident of experimentation.
Gotta love thelastleroy's blasphemy mod, if nothing else for the balls it takes to gut an amp and start from scratch.
When I demo'd and instantly purchased my nomad 100 head, I could swear it was hooked into a Recto 2x12 with v30's.
Got it home, and poof.....nfg with my 1x12 open back C90 lonestar cab.
That said, it isn't only the speaker. Lifting the NFB is a design feature of a lot of modern boogie high gain amps. Also, that R/C network after the feedback resistor revoices the amp so that it doesn't have the sonic footprint that other amps like the Heartbreaker have.
I'm working out a mod for Ch3 that will surefire be a major optional improvement.
The good thing about a marginal amp is that it stimulates an awful lot of education...It's actually a pretty decent 2 out of 3 channel amp between the clean and ch2. The lot of us will be employable as amp techs by the time we're finished with it. The similarly notorious Formula Pre went through some significant modding research, and by the time it was done, the lead channels were pretty asskicking. There's something special about it's ch3 now that I bet an amp company couldn't design for. Just a lucky accident of experimentation.
Gotta love thelastleroy's blasphemy mod, if nothing else for the balls it takes to gut an amp and start from scratch.
I agree on the NFB but would say it depends on style. Mesa's new technique is to have it switched by channel. Usually a lot of NFB for clean channels, and then selectable for dirty channels. They usually will call the selectables settings as Raw/Vintage/Modern as used on Rectos. That corresponds to A lot/ a little/ and no NFB. So I would say the NFB is probably good for Channel 1, debatable for the Vintage settings on Channel 2 and 3, and not needed for the Modern settings on Channel 2 and 3. I am thinking about going with an On-Off-On switch so I can simulate the three settings. Stock, additional resistance (less NFB), no NFB.
Also, has anyone tried first removing the preset presence circuit (R/C) hanging off of the NFB, without removing the NFB. I would be curious about first revoicing the NFB before removing it. A lot of great Mesa amps have NFB but simply not that preset presence circuit. The voltage divider ratio is pretty normal, so maybe knocking that preset presence off would improve the NFB sound first.
Also, has anyone tried first removing the preset presence circuit (R/C) hanging off of the NFB, without removing the NFB. I would be curious about first revoicing the NFB before removing it. A lot of great Mesa amps have NFB but simply not that preset presence circuit. The voltage divider ratio is pretty normal, so maybe knocking that preset presence off would improve the NFB sound first.
earachemyeye
Well-known member
I figured that r/c circuit had something to do with voicing the amp. I haven't gotten into the math so I don't know what exactly it's doing. After some weeks of playing mine I've decided to keep the NFB to the low side although ch. 3 sounds killer in vintage mode with less NFB. Very Van Halenish. Ch. 2 is to fuzzy sounding without NFB. Sounds like crossover distortion to me, yuck. Too much bass in there that I can't dial out. I tried getting some readings with the MM while it was cooking but it pops if I touch one of the legs on the pot so I'm not gonna beat it up like that. Maybe the best alternative is a rotary switch with a bunch of resistors of different value going up from stock. I have one but I'm not convinced to put it in yet. Kinda like it where it is. I sent a bunch of pics to Nomad Express and he said he would post them but he hasn't yet. I'd be interested in a ch. 3 mod that fattens it up some. Maybe addding a touch of 500k,800k and 80k? Seems to work wonders for mine with an outboard eq. I have a 1x12 55 with el34's in it.
Well, just lifted the 2.7K resistor hanging off the NFB to ground. Basically removes the fixed presence circuit off of the NFB. Like it better now and I did not altogether remove the NFB, just revoiced it. I believe part of the benefit of removing the NFB is that you remove the fixed presence circuit which IMO hurt the tonal balance. I always found channel 3 a little to fizzy and was rolling back the trebel, much better after removing the presence circuit. By removing this you are allowing a more equal amplification across the frequency spectrum while the existing presence circuit favored more mids, and even more trebel.
I would rather have all frequencies be equally amplified and use the EQ to shape verse have the amp automatically voice itself in only one way. NFB is not a bad thing so you should all consider whether you want to change the power section's dynamics (NFB) or frequency response (fixed presence RC circuit), or both.
Also went from reverb mod v1 to v2 (lowering the 330K resistors). Much better reverb performance now.
I would rather have all frequencies be equally amplified and use the EQ to shape verse have the amp automatically voice itself in only one way. NFB is not a bad thing so you should all consider whether you want to change the power section's dynamics (NFB) or frequency response (fixed presence RC circuit), or both.
Also went from reverb mod v1 to v2 (lowering the 330K resistors). Much better reverb performance now.
Glad to hear you did this and are satisfied with the results.
I've thinking that a potentiometer is probably the right way to go on that part, and if it were a push or pull switch style pot, all of the nfb could be removed as well through the switch part.
I bet there is more meat in the lower mids, which is needed, but probably have to roll the bass control down to about 10:00....
Give us your before and after settings for ch3?
I've thinking that a potentiometer is probably the right way to go on that part, and if it were a push or pull switch style pot, all of the nfb could be removed as well through the switch part.
I bet there is more meat in the lower mids, which is needed, but probably have to roll the bass control down to about 10:00....
Give us your before and after settings for ch3?
earachemyeye
Well-known member
Nice post. I think the same about ch. 3. I was using an eq to remove the fizz in modern mode. It's a killer channel with a few tweeks to the voicing. I'm using vintage mode now. I hated it before, thought it was a muddy mess. Less NFB seems to have cured that. So here is the total package: switcheable NFB levels and switcheable voicings for each level :roll: WTF, I must be on the Marshall forum.
Well, you bring up the right point, and the right solution.
The Nomad Ch3 is a bit of a bastardization of the rectifier red channels, except those amps had an extra gain stage, but less gain per stage, and had switchable nfb and presence, I believe, including the tremoverb.
The vintage and modern setting on the Nomad switch out a resistance toward the end of the preamp so as to overdrive the PI from the preamp directly, rather than through a reduction of nfb as in the other amps.
However, what would it take to have switchable NFB...Does anybody know what part and how to piggyback on the existing switching network to make that happen, or is a whole new PCB board with new switching networks required for that?
Perhaps the switching relays that chooses between Ch2 or Ch3 at the gain pot stage maybe could be interchanged with a relay with one more pole (if they make em and they fit...), to at least partially accomplish this.
The Nomad Ch3 is a bit of a bastardization of the rectifier red channels, except those amps had an extra gain stage, but less gain per stage, and had switchable nfb and presence, I believe, including the tremoverb.
The vintage and modern setting on the Nomad switch out a resistance toward the end of the preamp so as to overdrive the PI from the preamp directly, rather than through a reduction of nfb as in the other amps.
However, what would it take to have switchable NFB...Does anybody know what part and how to piggyback on the existing switching network to make that happen, or is a whole new PCB board with new switching networks required for that?
Perhaps the switching relays that chooses between Ch2 or Ch3 at the gain pot stage maybe could be interchanged with a relay with one more pole (if they make em and they fit...), to at least partially accomplish this.
Question came up around my bass settings after removing the RC fixed presence and the answer is no change at all. I wanted more bass in the mix and this simply helped. I have always run an EQ in the loop with a V to re-voice the amp but I have now softened the V shape a lot. I also need to turn the treble up on channel 3. I used to run it low (10 o'clock) but now run it at 11:30 and find that there is less fizziness as I turn the gain up. I also think the higher treble settings deliver better gain on a Mesa, I just could not handle the fizziness it created on this amp. The Presence (treble cut) control works better now too.
A few other things I did to get the sound I wanted was put TungSols in V1 and V3 (Mesa JJ style in other positions) which helped every channel, as well as run a Ross compressor with level high and sustain low to drive channel 1 (ala Andy Timmons) and the clean sound is amazing.
The only debate left for me is I keep switching between a 12ax7 and a 12at7 in the PI slot and can not decide which one I like better since they both have pros and cons in how they sound in this amp.
A few other things I did to get the sound I wanted was put TungSols in V1 and V3 (Mesa JJ style in other positions) which helped every channel, as well as run a Ross compressor with level high and sustain low to drive channel 1 (ala Andy Timmons) and the clean sound is amazing.
The only debate left for me is I keep switching between a 12ax7 and a 12at7 in the PI slot and can not decide which one I like better since they both have pros and cons in how they sound in this amp.
I'm loving an AY7 in the PI of my heartbreaker, smooths out the tone and has no strange artifacts going on allowing the natural expression of the power tubes to come through. (I run EL34's in my heartbreaker). i'll be trying an AT7 when I get around to ordering a bunch of new tubes. Can't remember what I have in the PI of my Nomad, but Ch2 is very very similar to the hi gain setting of the heartbreaker lust channel, so i can only believe I'd prefer an Ay over an AX.
There's a fellow with some youtube clips of his Les Pauls through the Nomad Clean Channel with a tubescreamer boost, and the tone is phenomenal. I've always held that the Nomad's clean channel is one of, if not the best in the business, for a post-V1 tonestack approach anyway, so no surprise you're getting Andy Timmon's quality.
If the Nomad was configured with only Ch1 and Ch2, people would like it. Ch3 sure buggered its reputation, but ya know, I've found if I back my volume off on my guitar, the Ch3 fizz disappears ala marshall.
All said, though, the fixed treble boost in the NFB really has to go, as you've found. I've been thinking that mesa did this to revoice the 6L6's that come standard in almost all their amps to have more of a EL34 quality. By comparison, the Heartbreaker has a standard NFB, and the low-mids are so powerful with 6L6's that they melt your face and make your eyeballs shake out of their sockets, which I don't like....which is one reason why EL34's are way better in that amp....so you see why Mesa may have done this to the NFB.
My current train of thought is that Tungsol EL34B's may be the perfect match for the stock nomad, so I'll be purchasing a set soon. They are EL34's with the bottom of a 6L6 and with the Nomad's weird NFB, they should be a good match.
There's a fellow with some youtube clips of his Les Pauls through the Nomad Clean Channel with a tubescreamer boost, and the tone is phenomenal. I've always held that the Nomad's clean channel is one of, if not the best in the business, for a post-V1 tonestack approach anyway, so no surprise you're getting Andy Timmon's quality.
If the Nomad was configured with only Ch1 and Ch2, people would like it. Ch3 sure buggered its reputation, but ya know, I've found if I back my volume off on my guitar, the Ch3 fizz disappears ala marshall.
All said, though, the fixed treble boost in the NFB really has to go, as you've found. I've been thinking that mesa did this to revoice the 6L6's that come standard in almost all their amps to have more of a EL34 quality. By comparison, the Heartbreaker has a standard NFB, and the low-mids are so powerful with 6L6's that they melt your face and make your eyeballs shake out of their sockets, which I don't like....which is one reason why EL34's are way better in that amp....so you see why Mesa may have done this to the NFB.
My current train of thought is that Tungsol EL34B's may be the perfect match for the stock nomad, so I'll be purchasing a set soon. They are EL34's with the bottom of a 6L6 and with the Nomad's weird NFB, they should be a good match.
Oh yeah....I also run Tungsol's in V1, and 1960 Raytheon Long Blackplates in cathode follower positions. Its a great combination. The tungsols seem to have characteristics that bring to mind what people say about VOS Mullards, although I've never had the opportunity to try one.
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