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Discussion Forum for Mesa Boogie Products
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PostPosted: Tue Aug 08, 2017 9:33 am 
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Bottle Rocket

Joined: Tue Aug 08, 2017 8:05 am
Posts: 4
Hi Everybody,

I have joined this forum purely so I can comment on the Nomad Power Supply mod as detailed by soundguruman. I normally just lurk, cherry picking gems magnanimously proffered by other benevolent forum posters, but no-one has posted any post mod feedback so I decided to go for it and give soundguruman the credit he deserves.

I hope its ok to resurrect such an old thread...

Also, its a long post, but there is a lot to say...

I bought my Nomad 45 112 about 10 years ago after I played a gig where the back line was provided and to my surprise I was supplied with a Nomad 55 212 to use on stage rather than the cheesy amp I was expecting. I really liked the amp for the time I had to use it during the gig. Obviously there wasn't too much opportunity to tweak and play but I just plugged in, switched to channel 2 and just used the volume on the guitar, not knowing about the solo switch and didn't bother with channel switching as I'd only had time to set up the one second channel. I liked the way the amp cut through on stage and in the mix so decided to get one for myself (I'd always promised myself I'd get a Mesa Boogie one day and that day had come!).

I opted for the 45 112 for its size and convenience for gigging and smaller stages. I was unaware of the EL84/6L6 difference in the power stages.

I re-tubed with JJ matched quad EL84s and high gain 12AX7 preamp valves. The amp sounded ok but didn't blow me away and certainly didn't seem to have the clarity of the 55 I initially tried. I don't know if 55 amp was stock and just a lucky good sounding one. There seems to be quite a lot of variation in both sound and reliability in the Nomad range from what I've read online.

I came across this forum and the "mud mods". People were raving about how the mods brought the amp to life so I thought I'd give it a go. The mods certainly improved the darkness issue and gave the amp more "airy" breath and top end and yet it still didn't quite sound right. Kind of edgy and brittle?

I did the reverb mod too and whilst this made the reverb more audible on the overdrive channels 2 & 3 it was quite horrible and distorted on the clean channel where it had sounded lush previously.

Years later (now) I decided to reverse the reverb mod and so looked up the page I bookmarked with the mods on in case I wanted to un-mod at any time in the future. This was when I came across the mod suggested by soundguruman to replace some of the electrolytic capacitors in the power supply. I read his description of the problems caused by the power supply design. His conviction that this was indeed why the amp didn't perform as well as could be expected made me curious to try it.

I located the schematics on line to be able to interpret the instructions.

I have to concur that this mod is not for the faint hearted or inexperienced (I am an IT technician and ex wireman and comms engineer so have access to a temperature controlled soldering iron and solder sucker). It took a while finding the right diameter capacitors with the correct lead pitch but a company called Semicom in the UK and on eBay had both the 47uF & 22uF electrolytic capacitors in 12.5mm case diameter with 5mm lead pitch, 450V rating, 105C temp rating & 20,000 hours MTBF Nichicon manufacture. First of all I reversed the previous "mud mods" to put the amp back to standard

There is a lot of work required to be able to get to the underside of the board. This is necessary to be able to de-solder and re-solder the radial electrolytic capacitors.

As soundguruman suggested none of the other mods are needed after the power supply is sorted by stiffening.

The modded amp is completely different! The clean channel now has some sparkle. Its easier to hear the tone controls working. It sounds much nicer when "pushed" and overdrives warmly and is more rounded.
The overdrive channels - channel 2 is now thick and fat but warm too, much creamier; channel 3 is now usable! It has more bite and clarity rather than just fizzy mush. It can be very heavy!

When cranked the amp just seems to get nicer as the output increases. I haven't had a chance to try it in a band environment but I've found myself playing, sat in front of the amp just listening to the tone and dynamics. I don't know if anyone else has tried this mod but I just had to comment as no-one else has. Having tried both approaches I felt compelled to join up and post this for anyone else who isn't satisfied with their Nomad, but like me feels that the amp could sound so much better

Soundguruman said to another poster that they would thank him after performing this mod; I haven't seen a reply but I signed up purely to be able to do that - THANKS Soundguruman you've certainly lived up to your username in my experience 8)


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PostPosted: Tue Apr 24, 2018 5:43 pm 
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Bottle Rocket

Joined: Mon Nov 17, 2014 10:06 pm
Posts: 6
Did the cap augmentation posted by soundguruman and the amp can deliver considerably more low end punch, where before it just went to mush. Checking other mesa 100 watter schematics I noticed that all of them have two or three times total capacitance on these nodes than the nomad does. It looks like mesa wanted to experiment with making the amp spongey by using smaller caps. I like dual recs in tube rec mode, but the nomad just lost too much fun as it was.
Removing the board is pretty difficult. Much easier to piggyback more caps over the nodes, or strap in the caps near the air vents and run leads.


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