nomad mods

[balokker]

One more mod to try on your Nomads: desolder one of the wires on the presence pot on channels 2 and 3. This circuit is a variable low pass filter that loads down the signal even when the pot is at 100k. I was was very happy with the extra punch I got.

 

[balokker]

Can any techs here explain how the vintage modern switch works on the Nomad? From the schematic it looks like selecting vintage throws another 220k onto the top side of the 100k MV pot, effectively lowering volume. But vintage has a slightly warmer sound as well. Not sure why that happens.

link to schematic:
http://schems.com/manu/mesaboogie/boogie_nomad100.pdf

edit: I think I see whats happening. That 220k resistor effectively gives you what amounts to a 320k pot without a bright cap, hence the darkening in vintage mode. Seems like a better solution might be a small switchable bright cap...? That would be an easy mod to try as well..

 

[VonRecktofen]

Hey Gang,
Better late than never, but longstory short, I bought a Nomad 45 2 x12 back in '02-'03, used it a little, packed it away, now I'm breaking it back out to jam, etc.
What Mods should be done to improve it's sound? I also use a POD Pro Rack Amp Modeler, and I have used the Nomad just as a power amp (pumping Pod signal into "Return" on the effects loop with a 1/4 plug inserted into the "Send"), but overall, I guess I'm underwhelmed with this amp...Had a Studio .22 back in the late '80's that I regret selling, thought that this 45 with 4 EL-84's would be greater...
Somebody convince me to keep this guy and mod it, or what is the market like for selling it?

Thanks for any ideas!

Franz in NJ

 

[Koreth]

Can any techs here explain how the vintage modern switch works on the Nomad? From the schematic it looks like selecting vintage throws another 220k onto the top side of the 100k MV pot, effectively lowering volume. But vintage has a slightly warmer sound as well. Not sure why that happens.

link to schematic:
http://schems.com/manu/mesaboogie/boogie_nomad100.pdf

edit: I think I see whats happening. That 220k resistor effectively gives you what amounts to a 320k pot without a bright cap, hence the darkening in vintage mode. Seems like a better solution might be a small switchable bright cap...? That would be an easy mod to try as well..

I will have to find the frequency response graphs from the simulations I did of this part of the circuit, but you are effectively correct. With the resistors in place, there's more attenuation of the signal, in the highs especially. But the overall gain structure isn't changed.

IMO, these resistors would be better placed between the 2nd and 3rd gain stages (V4a, & V3b) of channels 2 & 3. Altering the value of either of the two 1Meg resistors between V4a and V3b would let you affect how much of the signal from V4a is fed into V3b, and thus how hard V4a drives 3b and causes it to distort. This would have a much larger effect on the tone of Channels 2 and 3 than the stock vintage/modern switches do.

If I can find my old simulations of the Nomad's circuit, I'll play with them and see what I can come up with.

 

[bugsy62]

Hi there, I bought my Nomad 55 about two weeks ago, and having completely revalved it - I'm beginning to have fun with it. However, having spent weeks reading up on these amps I'm inspired to go ahead and do a couple of the recommended mods. I'm gonna do the efx cap mod and the NFB mod.
My main question is: can I just disconnect the reverb-three wiring from its pot. and re- use the pot as a variable NFB control? If so, do I need to put a resistor somewhere in the circuit, and what value do I need to use? If that pot isn't suitable- perhaps somebody could give me an idea of which components I would need for this mod.

I have found that by reading the manual a few times and then sitting and playing with the controls for several hours I have come up with some pleasing settings. However, I am hoping to gain some clarity in the sound and lose some of the buzzy overtones I am hearing.

By the way, I am super-impressed by the dedication and generosity of the members of this forum. Seriously, if it wasn't for the postings on this forum, I would be thinking that I had just spent a lot of money on a very average sounding amp. Clearly all is not lost, and I'm looking forward to turning my Nomad into a tuneful fun-to-play amp.

Many thanks for reading/ heeding my cry for help.

 

[Andree88]

Hi, I've bought a Nomad 100 head (done mud mod and reverb mod).
I just want to know if it's possible to do a mod to channel 3 adding gain (I want to know if it can sound like if it's boosted by an od. I mean, I want the sound and amount of gain like when I push it with my TS Mini).
I red that changing a resistor near V3 will add more gain to CH2 and CH3.
What should I do? Can You help me?

I don't want to need an OD to have a badass sound on my lead solos.

Thanks!

 

[Koreth]

Hi, I've bought a Nomad 100 head (done mud mod and reverb mod).
I just want to know if it's possible to do a mod to channel 3 adding gain (I want to know if it can sound like if it's boosted by an od. I mean, I want the sound and amount of gain like when I push it with my TS Mini).
I red that changing a resistor near V3 will add more gain to CH2 and CH3.
What should I do? Can You help me?

I don't want to need an OD to have a badass sound on my lead solos.

Thanks!

Take a look at the schematic here. There are a few resistors near V3a or V3b that if changed, will increase the gain of the channel 2/3 circuit at that point. If you don't understand tube circuits enough to pick out which resistors they are and why, I'd recommend against trying to mod for more gain by swapping a resistor near V3. Blindly swapping out resistors without understanding what they do and why runs a risk of damaging the amp.

However, I don't think increasing the gain late in the channel 2/3 circuit is going to get you what you want. It's not going to have the same effect as boosting the amp with an overdrive pedal. An overdrive pedal, depending on its settings, adds compression and clipping of its own, changes the eq balance of the signal going into the amp, and raises the signal level. That in turn causes V1a to drive V4b harder, which in turn drives V3a harder. A change in the signal entering the amp has effect through the entire cicruit, which will be difficult, if not impossible to replicate by making changes to the end of the preamp circuit.

Probably the simplest and easiest way to get the sound you like is to continue doing what you're doing now: boost the amp with an OD pedal. If you don't like having to do the foot pedal dance when switching to your lead tone, there's a number of devices you can buy that can switch multiple pedals with a single stomp.

If you want to make further mods to your Nomad 100 to improve its tone, check out the power supply mod described by soundguruman here. I've not done it yet, but his reasoning is sound. Unfortunately, it's involved. You have to disconnect multiple leads from the board so you can take it out of the chassis and get to the power supply capacitor leads on the underside. If you're not already experienced with soldering work and don't have access to a temperature-controlled soldering iron (that's important, you risk frying the board otherwise) and desoldering tools, you're better off to take the amp to a tech to have the mod work done.

 

[sentari]

It seems the pictures that Normad100 posted have been gone for some time. Can someone post them or point to/give some specific instructions to the mud and reverb mods?

 

[balokker]

Thanks for the mod list Optical.
I found that treble peaker to be a critical voicing factor as well. I went with 235k (two 470s in parallel) and 681pf.
What did you get from changing that 1M to 220k on V4a? Looks like it will boost the signal working with the other 1M on the grid.

 

[John Micka]

Hi all,
Reading this thread for a while and I must say a lot of work was put into this.
You guys are great taking the time to tweak these amps in for an improvement.
Well I have a question as I'm about to try a different output transformer on a Nomad 45 for a test.
The Nomad 45 I have has a blown output transformer, makes me wonder why its blown. I took it apart and found the short, the inner windings shorted through as they turned on the core at only one spot, this is a rewind job.
I noticed the circuit board previous owner did the mud mod I guess lifted the 2 little ceramic caps. (I replaced them back on the board)
Now I have added the SoundGuruMan Mod, (I'm sorry having lack of name) beefier power supply capacitance he stated took care of muddiness and he mentioned adding 68k resistance at the input jack. Also I added the parallel resistance to the reverb.

Anyways back to the output transformer, I'm going to try a Marshall 50 watt and was wondering if anyone tried this yet?
This transformer is about 5 times more steel on it than the standard one.
Some things that make me question is I don't know the impedance of the standard transformer and the winding ratio.
The Marshall really was built for 2 EL34's.
Also it would be interesting to hear the output of the beefier Marshall transformer (maybe).
I believe primary impedance is I believe 6.4kohms or 3.2k plate to plate and the Marshall has added a 16ohm speaker tap.

 

[John Micka]

I don't know any better.
When the Marshall 50watt output transformer was installed I got a huge hum from the speaker.
Tested another speaker still monster hum.
Only thing I can guess is a mismatch.???

 

[John Micka]

Okay, I got it done the Nomad 45 is repaired.
A member found me a transformer out of a rocket 44, it was the same output transformer.
Now I have questions.
This amp I did the power supply mod and before I closed it up I put on the resistors for the reverb mod.
After being on for about a 10 minute test, it has incredable power and punch.
I could feedback, controllable at any channel at volume below 5 easily.
Well I notice the huge amount of heat at the power tubes.
Has anyone installed any fan in the Nomad 45?
I believe it needs much more heat dissappation. Any ideas?
Or is there possibly something still wrong on this amp.
Incredable little amp, but I worry about the heat.

John