Nomad 55 mud mod

[Tommy_G]

Yep....That was my experience with my Express browsing. It had to have been speaker differences for it to be that dramatic.

If you're worried about your speaker, remember that all you're getting into the express effects return is a preamp signal. The Express power amp still controls the power level to the V30! All the signals in/out of the effects are approx. line level with the master levels at noon, although cleans may be a little higher because of the attack envelope of the signal.

I suppose though that the Express has EL84's or something, so you'd also be sort of checking out what the Nomad 45 would sound like. (maybe...I actually forget the power section of the Express)

 

[NomadExpress]

I have been thinking about all of this and one thing for people to consider prior to the NFB mod is the capacitor value for the FX mod. The design recommended mod is to take it from 5 nF (.005 uF) to 50 pf (47 pf). I was studying the curve and perhaps 83 pF or 100 pF would gently attenuate the high end and still exhibit an acceptably flat curve.

So I am thinking that picking a moderately higher cap value can possibly attenuate the need for the NFB mod.

 

[earachemyeye]

I've tried a few speakers in my Nomad 55 1x12. I settled on an Eminence Red Coat the Wizard. Nice round and warm sounding where the C90 to me was harsh and sterile by comparison.

 

[Tommy_G]

Always fun talking about amps. Wish I was more of an electronics guru though. I pour over schematics every night with only a very layman's understanding of what the different arrangement of components do. I do see the patterns, and have a basic idea of the functional blocks within a preamp schematic, but the details of resistor/capacitor networks and exactly what's being done to the tone makes my head spin.

I have 3 amps from the same basic program. Heartbreaker, Formula Pre, and Nomad - that was the lineage of that series, and in that order. The Heartbreaker introduced the 'Mk1 meets Marshal tonestack' as the Lust Channel. The Ld1 of the Formula, and Ch2 of the Nomad clone the Heartbreakers's Lust Hi Gain tones, plus or minus a little gain.

The Formula Pre took it a further step adding a 2nd Marshall tonestack Ld tone as Ld2, and the Nomad took that Formula Ld2 tone and put a mushy pseudo-rectifier flavor into it.

My Formula Pre isn't 100% stock. It had at least part of the "Andrew Mod" done on it (by me) which was a vast improvement. I can't recall exactly what was done, but for sure the 470 kohm resistor on the input of V1A was changed to a 1Mohm, and I think I changed a cathode bias capacitor from 1 uf to .68 uf or something to mitigate the bass flubbing that was ever-present on Lead 1.

I played the Formula for a few years into a SS power amp for my gigs (all I could afford at the time). It was love-hate - some nights it would sizzle with this spinning ethereal lead tone on the second Lead Channel, and other nights it was so dull and uninspiring that I'd want to huck it in a dumpster. I had never been really happy with Ld 1. So its been hiding in a rack for a few years.

Tonight I plugged it into the Heartbreaker Effects Return, and it sounded so awesome, beating the crap out of both the Nomad and Heartbreaker. I've only got New Pro tubes in it, and I got some top notch VOS in key positions in the Nomad and Heartbreaker. Go figure.

Even my wife who came down to give me crap for playing loud mentioned it was the best sound she's heard from my practice room in a while.

Wow, sometimes I do feel like I'm going backwards.

I don't believe I ever tested the Formula feeding the Heartbreaker power section, I gave it a try once on the Nomad power section, and gave up on it because it sounded like crap. I'm going to try it again tomorrow (into the effects loop and power section), and compare it to the HB.

So maybe my current struggles with the nomad really do go back to the Effects Return, the Power Amp caps, and the NFB loop. However - its clear from the Nomad schematic that there is a filter that accentuates certain frequencies during NFB. And while disconnecting the NFB may sound better than a poor stock design, I just can't believe that is the optimal configuration. NFB does so many great things for an amp in terms of feel and tone, and a total disconnect shuns the whole concept of it. Its bad philosophy. Again, the Nomad's power section is very rigid, almost like a SS, the Heartbreakers is such a joy by comparison, especially on the Curvaceous setting which has MORE NFB than the more rigid Bold setting.

I think I want a variable control NFB pot with a Real presence control hooked into the Nomad's existing filter network, as a starting place. That's something I'd take the soldering iron to do, if somebody could give me the details of implementation.

Anyways - tonight, I'm trying to figure out if there's a secret or two to be learned from the Formula Preamp lead channel Schematic as it would adapt very easily into the Heartbreaker or Nomad.

 

[NomadExpress]

....

I think I want a variable control NFB pot with a Real presence control hooked into the Nomad's existing filter network, as a starting place. That's something I'd take the soldering iron to do, if somebody could give me the details of implementation.
...

Let me look into it over the next few days, The basic information is here, I would like to get back into my amp and find the parts. Reverb is not working either... Ill need to look at that too.

 

[Tommy_G]

Thanks, NomadExpress.

I've got a fairly difficult technical issue that needs explaining.

I am trying to do an A/B comparison between the Heartbreaker and Nomad PREAMPS as sounding through the Heartbreaker Power Amp, using the Effect Send on the Nomad into the Effect Return on the Heartbreaker.

I put my guitar into an A/B box and A goes into my heatbreaker guitar input, and B goes to the Nomad guitar input.

Despite the switching, I can only get the Nomad Preamp to sound, and when I switch to the Heartbreaker input, its not total silence, but pretty close.

I just don't understand why this would happen.

I can do this successfully running the B cable to the Formula's input, and the Formula's Main output into the Heartbreaker Effect Return, and both sound depending on the A/B switch.

Weird? Or is this because of the Nomad's Parallel Effect loop which causes the Heartbreaker to backfeed its preamp signal to a possible lower impedance in the Nomad Parallel circuit?

 

[NomadExpress]

Tommy:

The explanation is quite simple. The Heartbreaker has a serial loop.

Plugging anything in a serial FX return jack effectively overrides any signal you get from the preamp, even if there is no signal sent to the return jack. Both the Formula and the Nomads have parallel loops so they won't exhibit this issue. The Heartbreaker will as it is a serial loop.

 

[Tommy_G]

Tommy:

The explanation is quite simple. The Heartbreaker has a serial loop.

Plugging anything in a serial FX return jack effectively overrides any signal you get from the preamp, even if there is no signal sent to the return jack. Both the Formula and the Nomads have parallel loops so they won't exhibit this issue. The Heartbreaker will as it is a serial loop.

At first I thought that too, except that that the HB preamp still comes through if I put my Formula Main Outs into the EFX Return of the Heartbreaker...it just doesn't work with the Nomad. I think the effects disconnect only occurs if you plug into the "send" side. If you just plug into the return, I think the signals mix according to the laws of physics...(of course, with the inputs being switched there is only 1 significant signal at any time, other than background noise.)

:? :? :?

 

[NomadExpress]

....

I think I want a variable control NFB pot with a Real presence control hooked into the Nomad's existing filter network, as a starting place. That's something I'd take the soldering iron to do, if somebody could give me the details of implementation.
...

Let me look into it over the next few days, The basic information is here, I would like to get back into my amp and find the parts. Reverb is not working either... Ill need to look at that too.

This is the basic Idea for a variable NFB mod with a full "Kill" switch, mimicking the Nomad 45 Extreme switch. I just slapped the image of a pot for representation, Any double throw- push pull would do. SPST is the minimum requred DPDT would work to, just remember to use the same "poles"/circuit.

Ill try to get to the presence mod this weekend. I wont be performing the mod unless someone says its to die for.

 

[Tommy_G]

Thanks!

Is there any specific voltage or amperage rating I need to pay attention to? I'm thinking there are pots that have a grand finale disconnect right at the end of the turn with a detente.

I wont be performing the mod unless someone says its to die for.

That would be my wife telling you after I get zapped.... :lol:

Speaking of which....is there any protocol for releasing the high voltage capacitors so zapping doesn't take place?

 

[NomadExpress]

I used a tiny toggle switch, rated at 125V.
something like this would be fine.
http://www.theguitarfiles.com/product_id-1771.html

Beware, some turkey on e-bay is selling them for $28.

Unplugging the amp and turning the switch and standby on for a few seconds should dissipate everything. Grab a cup of coffee and pull the power tubes to protect them (and the sockets). I leave the preamp tubes in.

Be gentle with disconnecting the reverb. I think I damaged the larger grey RCA cable. Now my reverb is intermittent and I trace it back to the RCA plug to the chassis. I think I can use a stereo RCA cable to replace it.

 

[Tommy_G]

Well done on the other thread that provides the visual reference. It would be nice to keep that thread as 'clean' as possible - only posting final results, not discussion.

So, thanks for the effort on that.

I also wanted to post something I've found to be helpful - a link to a description of what the various resistor capacitor networks do in a preamp.

http://www.regiscoyne.com/tech/preamp_mods/

Here's an interesting quote:

Think of capacitors as "tone windows"-the larger the window (value) the "bigger" (really, lower) the frequencies allowed through.

If you look at the difference between the Heartbreaker and Nomad's Power Amp schematic, one thing has always struck me as being out of whack: The Nomad uses a 0.047 and the Heartbreaker uses a 0.1 capacitor in the coupling between the PI and 6L6's. From the Quote above, that would imply that the Nomad isn't getting as full a range of lower frequencies as does the Heartbreaker...and when you play the two live - its a pretty obvious difference. The heartbreaker has far more girth to its tone.

Also, the Heartbreaker only has the 'stability' capacitors (I forget the technical name...?) on one side of the PI,. where the Nomad has it on both. The Heartbreaker sings, the Nomad doesn't. Wonder if having different frequency response on each side of the PI has some effect on the ability of the amp to sing (hi freq phase interactions caused by a filter on only 1 side of the waveform.)

 

[NomadExpress]

Thank you. I should put a note in there asking for just that... keeping the tread clean.

 

[timgman]

Pretty awesome information. I have the nomad 100 head and will be doing some of these mods in the relative future(when my brother in-law gets back in town for an evening of soldering)..

So far I am not that impressed with the touch / feel of my nomad 100. (through a marshall with the harsher celestian 75's). I've had the cab for decades and like the 75's so although they are harsh I like the "cut" they provide for live... I prefer V30's for recording though...

Any way, the touch / feel / harmonic response seems .. out of touch. all the EQ capability in the world and I just feel that the amp is a bit to compressed and flat..

Although some people may say it's the gain I do not think it is...

I come from the jcm 800 world where although an animal of an amp it is a one trick pony... It's a great trick though .

I want that intimate feel. the harmonic range feels on the nomad limited.
That is the only way I can explain it.

I f I could have touch sensitivity / full harmonic range with the 3 channels and features of the NOMAD I'd be in love. Of course that's prob why people get Marks ...
A Mark is not in my near future and I like to have a different amp than the common anyway..

What mods are recommended?
can the the loop mod be un needed with a loop cable?
can I just dump the NFB connection and be happy?
Thanks a ton..

 

[Mordacain]

I just performed the Mud and Parallel to Serial Loop mods today on my Nomad 45. To be honest, its not a terrifically drastic change with the way I have my EQ set currently. However, I have spent a lot of time tweaking with different tube types and speakers and run the amp in Extreme mode pretty much exclusively. I can still hear a difference, its a bit clearer and slightly more articulate. Clean is a bit more sparkly and lively.

I didn't get a chance to play with the loop to see if I can hear a difference with my POD HD500 in 4 cable mode, but I tested my Blackstar HT-DIST pedal in the loop (bypassed preamp) and I got signal...sounded like *** though; it sounded like that originally too though.

I made my mods easy to put back to stock in case I ever decide to part with the amp; I merely desoldered one leg of each capacitor for the mud mod and use wire twist cap to connect the loop for series (instead of soldering and insulating).

I also tried pulling the outside pair of EL84s to drop the wattage a bit (matched speaker ohms appropriately of course). Really doesn't make it any quieter in Extreme setting. In Normal it definitely dropped the volume a touch. The main thing was the loss of headroom. If I was going for a balls out classic rock crunch, I'd definitely try this (only on the 45 of course).

 

[Mordacain]

Pretty awesome information. I have the nomad 100 head and will be doing some of these mods in the relative future(when my brother in-law gets back in town for an evening of soldering)..

So far I am not that impressed with the touch / feel of my nomad 100. (through a marshall with the harsher celestian 75's). I've had the cab for decades and like the 75's so although they are harsh I like the "cut" they provide for live... I prefer V30's for recording though...

Any way, the touch / feel / harmonic response seems .. out of touch. all the EQ capability in the world and I just feel that the amp is a bit to compressed and flat..

Although some people may say it's the gain I do not think it is...

I come from the jcm 800 world where although an animal of an amp it is a one trick pony... It's a great trick though .

I want that intimate feel. the harmonic range feels on the nomad limited.
That is the only way I can explain it.

I f I could have touch sensitivity / full harmonic range with the 3 channels and features of the NOMAD I'd be in love. Of course that's prob why people get Marks ...
A Mark is not in my near future and I like to have a different amp than the common anyway..

What mods are recommended?
can the the loop mod be un needed with a loop cable?
can I just dump the NFB connection and be happy?
Thanks a ton..

The GT75s are definitely going to be a bit harsh sounding with the Nomad. I've played those with a variety of amps and they certainly work for certain types, but not sure about the nomad since its such a Mid-Heavy amp.

As far as mods, I'd definitely recommend the Extreme mode-switch mod to remove the Negative Feedback on demand. Though I pretty much leave mine in Extreme its good to have the option to drop the volume.

I'd also recommend trying some different preamp tubes out. This amp gets the majority of its tone from the preamp, so different preamp tubes really make a difference in affecting the amp's overall voicing and touch responsiveness. Here's a thread that has some information on different preamp choices:
http://forum.grailtone.com/viewtopic.php?f=4&t=53247

I think I'm going to try the Effects Loop mod (the mud mod mk2) but I need to get the replacement cap for that. I'm pretty happy with mine in its current state but I might see if there's any way of revoicing Channel 2 to have a more Mark II lead channel voicing eventually.

 

[NomadExpress]

What mods are recommended?
can the the loop mod be un needed with a loop cable?
can I just dump the NFB connection and be happy?
Thanks a ton..

The "Mud Mod" is a subtle one. It helps in band situations mostly, but is not the biggest change.
Replacing the .005uF cap with the 47pf cap is pretty much proven to be one of the biggest bang for the buck mod
I put in the NFB switch because I like the option of having it or not. I use it in both settings.

I recommend the cap replacement and the NFB mods. These will really kick the tone in.

 

[NomadExpress]

.....
I think I'm going to try the Effects Loop mod (the mud mod mk2) but I need to get the replacement cap for that. I'm pretty happy with mine in its current state but I might see if there's any way of revoicing Channel 2 to have a more Mark II lead channel voicing eventually.

That's your best bang for the buck. I went in and put the extreme switch in also ... kick *** performance. Amp is now a keeper.

 

[Tommy_G]

.....
I think I'm going to try the Effects Loop mod (the mud mod mk2) but I need to get the replacement cap for that. I'm pretty happy with mine in its current state but I might see if there's any way of revoicing Channel 2 to have a more Mark II lead channel voicing eventually.

That's your best bang for the buck. I went in and put the extreme switch in also ... kick *** performance. Amp is now a keeper.

The best amp tech in a city of a million people looked at the Nomad schematic with me, and said the NFB loop was "very unusual".

My current belief is that the treble dump part of the NFB (which actually creates a treble boost because the dump reduces the feedback) causes the balance of frequencies to go wayyy out of whack as you crank the master. Thus, everything becomes unhinged tonally as we approach "feel" in the power section. Which is probably why the disconnected NFB sounds 'better'...because at least it insn't unhinged....even though it probably isn't optimal either, particularly with 6L6 tubes which *need* feedback (EL84's don't).

I sure have a love-hate with the Nomad. I love that clean channel! And the pushed side of the Clean, too.

I've been continuing my research into the Nomad schematic, and lately I discovered that the the Ch3 voicing is about 90% the same as the Rectoverb LD Channel. I don't exactly know whether REctoverbs were loved or hated, but I'm not an OTT high gain guy, and I try to force that channel into a mid gain blues lead tone, and it just isn't toneful enough for blues - too hard and cutting with inarticulate mush in the low mids. So, lets face it, I'm not using it as intended.

If I ever fix up that NFB, i'll see how it sounds before I mod Ch3. But for now, I'm in love with my Heartbreaker.

 

[Mordacain]

.....
I've been continuing my research into the Nomad schematic, and lately I discovered that the the Ch3 voicing is about 90% the same as the Rectoverb LD Channel. I don't exactly know whether REctoverbs were loved or hated, but I'm not an OTT high gain guy, and I try to force that channel into a mid gain blues lead tone, and it just isn't toneful enough for blues - too hard and cutting with inarticulate mush in the low mids. So, lets face it, I'm not using it as intended.

If I ever fix up that NFB, i'll see how it sounds before I mod Ch3. But for now, I'm in love with my Heartbreaker.

Yea, Channel 3 is pretty much your hard rock / metal channel and while I liked the low-gain tone, it definitely isn't going to work with everything. For blues, I find that channel only works with single-coils, otherwise there is definitely a bit of mush. The Gain definitely works to tighten the response of that channel. I run mine around 1-2 o'clock (of course I am going for a heavy rhythm tone on that channel).