Nomad 55 mud mod

[rolue]

In response to the mud mod:

I also found the Nomad 55 to be very muddy, so I did the mud mod that nomad100hd proposed.
It did make a difference to me, but I still didn't like the sound. Especially channel 3, which also has annoying highs. I started looking at the NFB circuit in the amp, because the presence controls aren't the traditional kind.
I was going to change the 39k resistor off the NFB to 82k, and take out the 2.7k resistor and replace it with a 5k pot, so it would resemble a normal presence control. When I took the NFB wire off the 8 ohm tap to start the mod, I decided to play the amp without the NFB connected.

WOW, what a difference. No mud and no nasty highs. I didn't play at band levels, but did play very loud. I might put the modded circuit in anyway for more versatility, or to control what might result in unwanted feedback from not having a NFB circuit.

I'll post back when all mods and testing is done.

Any comments on this? Has anyone ever tried this?

 

[rolue]

For those interested, I'll be testing at band levels this week end, and will post back.
Would still like to know if anyone has done this before.

 

[rolue]

Amp sounds better without NFB. Clears up the amp and takes out the mud.
Very easy to do.Just take the purple wire off the 8 ohm tap, and put a switch between it to turn it on and off.

 

[Tommy_G]

Amp sounds better without NFB. Clears up the amp and takes out the mud.
Very easy to do.Just take the purple wire off the 8 ohm tap, and put a switch between it to turn it on and off.

I think the Nomad 45 has a switch (Extreme switch) that does exactly that; removes or attenuates NFB....and from what I read, most people shut the NFB off on that amp....So it would make sense that you would have similar results with the 55. Also, I think, but am not 100% sure, that the heartbreaker "bold/curvaceous" switch performs the same function. I have a Heartbreaker, and I run it exclusively on bold, which is the reduced NFB setting.

However....an awful lot of great sounding amps use NFB with success, so my thinking is that your discovery is simply covering over a fundamental problem with the Nomad design.

In the famous Nomad Mods thread, you will see that Koresh did an awesome job showing that the EFX return circuit is the main source of the tone-sucking mud. My experience has been that any outboard preamp plugged into the Nomad's EFX return sounds like crap. Thus, my sensibilities are that Koresh is correct. AND the Nomad isn't the only Boogie amp to use that EFX return componentry. Thus, a lot of muddy Mesa amps might find glory with the same change, including the Heartbreaker.

I've yet to do the mod, but I think he's on the right track in terms of addressing the fundamental problem.

That said, the ability to change the amount of NFB is a nice to have function in an amp.

 

[Tommy_G]

See below

 

[Tommy_G]

I did an experiment with my Mesa Formula Pre, which also has an effects loop, and it has been advertised by Boogie that the Formula takes direction from the Heartbreaker, and I'm pretty sure that the Nomad took direction from the Heartbreaker and Formula - so, shall we say, cut of similar cloth?

I ran two identical George L's from the Formula
1) from EFX Out
2) from Main output

Thru an A/B switch and into my ADA Ampulator, which Fed a ProTools Mbox set at 96kHz sample rate.

I set the effect out level (using the Volume Masters) and then the Main Output Level (using "Output") to be identical in amplitude, at least as good as my ear can hear levels while switching back and forth between the two output sources.

I changed all manner of eq settings on the ampulator, and even listened to the signal dry, and there was a very very slight, almost unnoticable improved clarity on the EFX out vs. the Main Outputs. There was a subtle preference in 'feel' between the EFX Out vs. Main Outputs, and in evaluating the subtlety in detail, concluding most of the tonal difference was in a slight improvement of the articulation of pick attack.

So, I would suggest, in spite of my support for Koresh's theory that the EFX return coupling is a possible source of mud, I have to suggest that at least on the Formula, there isn't enough difference to worry about.

As a disclaimer to my change in opinion, I will say that I worked long hours to pick tubes for the Formula that made it acceptable sounding, and it could very well be that I have a bright tube in the EFX or PI stage that effectively countered any tonal loss in the Effects return side....

 

[Tommy_G]

Amp sounds better without NFB. Clears up the amp and takes out the mud.
Very easy to do.Just take the purple wire off the 8 ohm tap, and put a switch between it to turn it on and off.

Going back to this...I looked at the power amp schematics of the Lonestar, Heartbreaker and Nomad 100.

The Lonestar uses a 820 ohm resistor in the feedback loop, of which there is 100 ohm voltage dividing resistor dumping to ground.
The Heartbreaker has a selectable 1k or 10k resistor (bold/curvaceous) with a 100 ohm voltage dividing resistor dumping to ground.

The Nomad parts company with that trend. It has a 39k dividing against a 0.1 uF capacitor in series with a 2K7 voltage dividing resistor, the two of these parallelled with a 4k7 resistor. This would be expected to have a filtering effect on the negative feedback....

The 2k7 and 4k7 in parallel create an equivalent series resistance of 13Mohm.

You can see this is very different than most of Boogies Power Amp designs in that respect.

I wonder what the effect of it is? Koresh? SPICE?

 

[Koreth]

What matters is not the absolute values, but the ratio, as they form a voltage divider which determines how much of the negative feedback gets fed back and how much gets dumped to ground. The 820/100 arrangement is the same as found in many Fenders. Given the target market for the Lone Star, that makes sense. The Recto, SLO 100 and the Nomad (and probably a few others I'm not remembering at the moment) all share the 39k/4.7k arrangement, which curiously, is the same voltage divider ratio as found in the Lone Star and Fenders: 8.2:1.

The filtering provided by the .01µF cap would be the presence control, if there were a pot there to adjust it. It is how the presence control works in most amps. Since negative feedback actually reduces the gain of power amp, dumping an extra bit of that negative feedback to ground in the mid and high frequencies causes the power amp's gain to go back up at those frequencies, giving mid/high frequency boost. The 2.7k resistor in series with that effectively limits how high the presence control can be turned. A similar arrangement can be found in the DC5, except it has pots by that cap/resistor arrangement making that boost adjustable for a presence control. In the Nomad, since there is no pot, it would be like having one turned all the way up. Thus, in the Nomad, the upper mid frequency boost in the power amp is running almost full tilt, and our Presence is a high frequency cut in the tone stack instead.

4.7k and 2.7k resistors in parallel give effective 1.7k? to ground, not 13Meg?, but only neglecting the .01µF cap. At DC (0Hz), the cap acts as though it had infinite resistance, and so you can neglect it and the 2.7k. As frequency goes up from zero (and thus becomes AC) the charging/discharging action of the capacitor makes its apparent resistance (impedance is actually the correct word here) go down, becoming significant at about 2.8kHz (the -3dB point of the filter formed) according to the SPICE simulation I just threw together. Since since we're taking away negative feedback, this becomes a 3dB boost at 2.8kHz At 10kHz, that's a 7dB boost.

I'm surprised you find the Nomad less muddy with no negative feedback. Negative feedback helps dampen the influence of the speakers upon the gain of the power amp. Look at the frequency response chart for many popular guitar speakers. You'll see a big boost somewhere in the lows or low mids, where the speaker is most resonant. With no negative feedback that should translate to a big boost in the lows and low mids from the power amp and no high frequency boost. But, if it sounds good to you, then cool.

 

[Tommy_G]

Thanks for the great explanation, Koreth.

I see I misinterpreted the 4k7....thanks for clearing that up.

The original poster (who I was responding to) disconnected the NFB, so I can't confirm that the amp was less muddy. Per your reasoning the amp should have more highs with the NFB and filter.

Koreth, have you actually changed out the cap in the EFX Recovery Stage, and noticed a difference? My only comparison was using the Formula, which I think has a similar EFX Recovery componentry as the Nomad, and as I mentioned above, could barely hear a difference, ignoring the fact that I've chosen my tubes very deliberately, and that was 4 years ago, so can't quite recall how and why I came to the tube selection I currently have. What are your current thoughts on muddiness?

The other thing the Board members should be thinking about is why Channel 3 sounds so shitty above about 11:00 on the drive channel. Below this, there is boatloads of what sounds to me like (what has been described as) inter-mod distortion (or some-such thing I was reading about 10 years ago), which gives it a wicked crunchy tone at low gains, but I suspect becomes problematic as the gain goes higher.

I have a huge problem with the archetecture of the Nomad. That is the clean channel V1 is shared with both Channel 2 and Channel 3 lead channels, which makes every tube selection a compromise. The Heartbreaker at least has the advantage of completely independent toneshaping tube paths on Channel 1 vs. Channel 2. That said, the Nomad is still my #1 gigging amp. There's just something about a low gain Channel 3 with the neck pickup that you can't find anywhere else.

 

[Koreth]

Truth be told, I have not made any changes. Shamefully, I've had the opportunity to do so until recently, but haven't taken advantage of it. Right now my Nomad's on loan to a buddy of mine.

What I find strange is people finding Ch 3 to be the muddy one. I've never found Ch3 to be muddy. It has always been channel 2 for me. Ch3 for me has always been tight and bright, and Ch2 sounds bloated by comparison. And when I was gigging the Nomad, I was running my gain plenty high, too, 1:30 to 2'oclock, and it sounded great to me for lead and med-high gain rhythm. The guy I'm loaning it to right now runs the gain even higher, and makes it sing.

I do intend to revisit this once I get it back. Ideally, I'd pick up a 2nd Nomad and leave one stock so as to be able to have a true A/B test, uncolored by the rose lens of memory.

 

[Tommy_G]

I like my Ch2. I was footswitching between my Heartbreaker Ch2, and Nomad Ch2, and I can get them within a few percent of sounding the same, probably due to tube differences in them.

I guess the way you set them depends on what you expect out of them. I try for a really thick, fat, and punchy tone, and invariably end up with my gain at 1:00-3:00, Treble at 1-1:30, and mids at 1:30-2:00 (mids always slightly higher than treble), presence about 11:00, and bass anywhere it sounds right in the room, from 8:00-dimed. Note that the treble has the affect of changing the center freq of the mids while also adding or subtracting treble. In a Marshall tonestack, the Mids add mid-highs which seem to give more brightness.

Give it a try. Its very clear and articulate and cuts through the mix really good on this setting. It sounds particularly good with neck pickups. Humbuckers or single coils. On the Bridge pickup, only sounds good with Humbuckers, but is a very hard rocking tone, whereas on the neck, its more hard bluesy.

Ch2 is no Mk2C+; Its vintage Mk1 meets Marshall tone stack. This channel just doesn't sound right to me with the mids scooped - it looses all its character.

 

[NomadExpress]

...... No mud and no nasty highs. I didn't play at band levels, but did play very loud. I might put the modded circuit in anyway for more versatility, or to control what might result in unwanted feedback from not having a NFB circuit.

OK so What I am thinking is "but did play very loud".... That's an over all volume increase brought on by the boosts described by Koreth here...

I'm surprised you find the Nomad less muddy with no negative feedback. Negative feedback helps dampen the influence of the speakers upon the gain of the power amp. Look at the frequency response chart for many popular guitar speakers. You'll see a big boost somewhere in the lows or low mids, where the speaker is most resonant. With no negative feedback that should translate to a big boost in the lows and low mids from the power amp and no high frequency boost. But, if it sounds good to you, then cool.

I am thinking...
Perhaps this is a perfect storm. Perhaps the mud was simply perceived because of the ABSENCE of frequencies, not an abundance of lows, so to speak. Doesn't the FX mod and the mud mod bring more frequencies into the audible mix?

I know I love the mud and FX mods, but perhaps the NFB mod would be the icing on the cake. It certainly sounds like the whole amp gets louder... As for perceived volume, the lower frequencies need greater dB increase for perceived balance.

Perhaps this is not so contrary after all and indeed complementary. I know that I really would like to cut some of the piercing highs too.

A push-pull pot will work for disabling and tuning the NFB. Electronically, what is the equivalent resistance of open, I am thinking a 1M Push-pull in series with the existing resistor (or greater R?) suffice?

g

 

[NomadExpress]

I just bit the bullet and did the NFB mod. I like it. I wired a defeat switch so it can be returned to the original configuration. It really is way louder and really does balance the amp after the FX loop and the mud mods. It is very much alive and responsive, warm and not muddled. This Nomad is a freaking monster now.

I would expect this to increase my tube wear, comments?

The last mod I am considering the reverb mod for channels 2 and 3.

 

[Tommy_G]

Thanks for your effort and insight NomadExpress. We'll get to the bottom of the Nomad's latent potential yet.

Here are some rambling thoughts for consideration:

1) I have always been disappointed that I couldn't get natural feedback except at earsplitting volumes. That would suggest a relative lack of fundamental and the first few harmonics, where the tone of any instrument is supposed to lay.

2) Demo'ed through a general assortment of similar Mesa amps on Youtube. My perception is always that the cleans are thinner than what they 'should be'. Again, fundamental and first harmonics.

3) Demo'ed through a general assortment of speaker shootouts on Youtube. Invariable, the Black Shadow leaves me unimpressed relative to many others (especially V30's and G12H30's, and Jensen C12N's)

4) The C90 was a speaker from the scooped hair metal days of the 80's.

5) Mesa appears to be subtly shifting their marketing to V30's over the last decade or so.

Screw the mods, I'm going to demo new speakers!

 

[Tommy_G]

NomadExpress - I was writing my little speech while you were posting on the NFB mod and pics.

I think what we need you to do is post an "after" youtube demo, and then reverse all your mods, and post a "before" demo

 

[Tommy_G]

Deleted...Oops

 

[NomadExpress]

Tommy, Thank you for your comments.

Thanks for your effort and insight NomadExpress. We'll get to the bottom of the Nomad's latent potential yet.
1) I have always been disappointed that I couldn't get natural feedback except at earsplitting volumes. That would suggest a relative lack of fundamental and the first few harmonics, where the tone of any instrument is supposed to lay.

I really think The FX and mud mods fixed this. It is very much alive, at much lower volumes. Feedback is definitely achievable at lower volumes. Also, the NFB really warms it up nicely (even with the C90).

.. My perception is always that the cleans are thinner than what they 'should be'. Again, fundamental and first harmonics.

Not anymore. Its bottom end is full round and articulate. Fatter and warmer cleans. Icepick practically gone.

3) Demo'ed through a general assortment of speaker shootouts on Youtube. Invariable, the Black Shadow leaves me unimpressed relative to many others (especially V30's and G12H30's, and Jensen C12N's)
4) The C90 was a speaker from the scooped hair metal days of the 80's.

Now that is interesting insight. I sort of agree. I am thinking that Mesa makes great amps, but the C90 has me scratching my head great amp, crappy speaker... nah Mesa knows what its doing. I was never impressed. They kind of remind me of Black Widows (Peavy) and your comment about the hair metal resonates.

I have to admit though, with the NFB mod, and never until I did the NFB mod was the bottom so round and articulate. The C90 sounded fine, for the first time really. lol.

5) Mesa appears to be subtly shifting their marketing to V30's over the last decade or so. Screw the mods, I'm going to demo new speakers!

I am not new to my soldering iron so it was easy for me to go in and replace a capacitor and lift the leg off off two others. Then The NFB is worth disconnecting and forgetting. I had the toggle so I figured what the hell. It cost me no money and 3 hrs of my time.

That said, I am certain that getting a hemp cone will freaking knock it out of the park. I recommend 100 W, at least. It's can get loud. The C90 is fine for now, but I hear ya about the V30s, I think I like the V30 in my Express 5:25. I love that little amp. I really like what the Nomad can do now. I feel the 6L6s. I think it can do a much better "Fender" now with the clean channel. The thing just sings. I have only played my Strat through it. I will plug in my Les Paul and report back.

 

[Tommy_G]

No question you are not afraid to jump into amps. and lets face it - you added value to your amp. All of what you did clearly would either improve the tone, or add to the flexibility of the amp (eg. NFB switch). Of course you know that the Nomad 45 has that NFB switch already, so you can just tell people you just modded it to Nomad 45 NFB specs...

The disconnected NFB clearly would put more (relative) lows back into the tone, which of course, makes it well more rounded at the bottom end like a fender.

What is probably more valuable than a total disconnect of the NFB is to reconfigure it with a resonance and 'true' presence circuit. If you look at the NFB already in place on the Nomad, you will see a filter network in place that actually may act as a crossover of sorts, with different feedback for lows vs. highs. Even putting a potentiometer across one of those to control the BALANCE of those two frequency ranges may be a better method of dealing with the tonal situation there than a disconnect switch.

I think you hit it with your statement that it is a great amp / **** speaker. That's my feeling too, except the C90 had a purpose in the past era of tone and wasn't **** per se. I think the world of tone is moving to archtop guitars and more blues friendly tones. We are long past the 80's - and will miss them and my teenage hair metal years very much. So, Goodbye 80's. Goodbye C90.

Well, here I am full of ideas, but won't actually open up my amp!

 

[Tommy_G]

A couple of further comments to your post ExpressNomad....

You mention the PV speakers of yore. I grew up on Widows and Scorpions...the only amps I could afford 15 years ago. The Scorpions from what I recall were well more 'crisper' than the C90, but alas, a bunch of the same characteristics...mid scoop, extended range - huge power handling capability. I think you're right that the Widows were probably closer to the C90 because they didn't have snap of the scorpions, and man did I get good metal tone with an Ibanez Supermetal and a Widow in the day.

Your comments about the Express 25 remind me of a browsing experience from a few years ago. I went into a guitar shop and for kicks sat down with the Express and was shocked at its killer tones. I came home to my Nomad and was very disappointed by comparison, but believed that maybe my tastes had changed and the Express was where my future was at. Then went out to another store a few months later with the idea that if the Express impressed me again, I'd probably come home with it. The one I tried sucked shyte, and I came home to my Nomad feeling pretty relieved at the whole thing that I couldn't justify parting company with amp and coin.

Well, this V30 vs. C90 thing puts a whole new kink in THAT experience! I never even paid attention to speaker complement, just assumed pretty much anything Mesa put out had C90's in it!

If there is one thing I could ask you to explore NOMADEXPRESS - is that you somehow hook your Nomad into your express V30's and Express into your C90's and give me your thoughts on my new thread re: speaker satisfaction. If it involves desoldering your speakers, forget about it - just plug the effect out into the effects return of the other amp.

If there is something clearly wrong with the tone, you may have to put a patch cord into the unused send/recieve to fully open the effects circuit. (At least that's what distant memory reminds me to do when I'm not getting the right tone out of one half of the send/recieve loop)

 

[NomadExpress]

And that's it .... until Thursday night, it was unthinkable for me to consider going at my Mesa with a soldering iron. I fell a little dirty for doing it in the end. The pictures and instructions on this site really helped and I appreciate it. I hope I can give back, so I documented it. I understand the natural reluctance to mod your amp, though If you lived near Oregon, I'd do it for ya....

I see your post about trying the speaker... I apologize, I'm not incline to oblige, only because the V30 is a 30 watt speaker and the Nomad can drive hella loud now. I don't want to risk the speaker. Now I believe I do have the converse experience I can speak to. I plugged the C90 into the Express and it sounded like *****. Colder than the V30. you can tell the C90 stood out as cold against the warmer V30.