Modulus JTM50

[Mcentee2]

About to start a Modulus JTM50 Black Flag build - super excited to get into this one. I chose it as it seems a great amp in itself as well as offering a few mod choices.

I play strat andLP and now SG - so run across all styles of noodling I don't play out in a band context so standing out in a mix isn't a concern - what is though is getting a great Marshall sound without either the bottom end farting or the top end "squelching" you can get with misapplied gain staging and eq.

Having looked at the main mods around, and how Ceriatone have laid out their All Access, I am trying to "downsize" the potential mod options to only those with the biggest bang for smallest change

As a general build I'll be using a single grounding point near the input jacks, using Merlin's guidance.

I would appreciate any views on the following expansive mods - I'll note my "top" with a *:

*1) Rectifier toggle - heavy duty switch between SS and gz34. I'll use the other side of the DPDT to get that 15k extra feed in the bias path to drop the resulting SS bias by just enough.

*2) Split/Shared Cathode on v1a - so far my choice for Bright side is 2.7k / .68uF. I know there are others, so have extra resistors/caps around, but might as well deviate a lot

3) This one I am not sure of, bright channel put a switchable in/out 0.0022uF in series with the existing 0.022uF

*4) Bright cap on bright channel - 100pF/off/4n7

*5) EQ slope change from stock 56k/250pF to 33k/500pF on a DPDT

(Keep the mixers at 470k and a bright channel 500pF mixer cap)

5) v2a cathode bypass toggle - 0.68uF /25uF - on the fence on this one too, but will try and see if it does anything "better". From what I have read, this one has downsides as well as benefits. Such as loss of touch response, can get very middy/pushy/spitty.

6) Presence Cap toggle for .1uF / .68uF - again, have to see what this sounds like before I make it permanent.

7) Post PI coupling staying at 0.1uF - I can't bring myself to put both these on toggles...just seems like a fair amount of work for poss not much change

8) Poss changing around the B+ Fuse location tot he HTCT, and also poss moving the first Filter Cap to before the Standby toggle - TBH I'm still confused by when that toggle is "useful" for a circuit - I usually ignore it anyway so will switch amps on from cold to off etc just using Power toggle.

That's about it I think, not bothering with any Master as I have a brilliant @JohnH attenuator being built alongside or messing with the NFB yet.

 

[neikeel]

Personally I would build a bog standard JTM50 and learn to play it.
If you make it look like a porcupine you will spend more time fiddling with all those mini toggles than actually playing it

 

[Marcomel79]

If you make it look like a porcupine you will spend more time fiddling with all those mini toggles than actually playing it

Couldnt agree more

 

[Mcentee2]

I hear you loud and clear!

I should have said my plan is to build as standard on Day 1 so I know it all works properly, then to tweak if I find particular responses or sound weren't as I want them to be.

Of course, fingers crossed the Day 1 standard hits th bull's eye

The only thing I would do on the build is the rectifier toggle as I can't seem to fall on one side of the fence easily....

I'm honestly 50/50 on SS Vs tube !!

A significant part of my pay off satisfaction from all this stuff is the tweaking though !!

 

[Ken Underwood]

Keep it as intended, if it needed all those mods then they would have been done by now

 

[AndyD]

Definitely build the standard JTM. I’ve just finished building one. Have a look at my building the classics post if you like.

 

[Marcomel79]

Definitely build the standard JTM. I’ve just finished building one. Have a look at my building the classics post if you like.

Its a beauty!

 

[Mcentee2]

Definitely build the standard JTM. I’ve just finished building one. Have a look at my building the classics post if you like.

Indeed - its your thread(s) that made me post here

This is the first time I have posted in Building the Classics, TBH I didn't know it existed as a forum as I usually shortcut straight to the Workbench forum, but today did a search for JTM50

Your build looks super clean and thought out

I like your above board cross wiring in black - makes it easy to see it's there!

 

[AndyD]

Indeed - its your thread(s) that made me post here

This is the first time I have posted in Building the Classics, TBH I didn't know it existed as a forum as I usually shortcut straight to the Workbench forum, but today did a search for JTM50

Your build looks super clean and thought out

I like your above board cross wiring in black - makes it easy to see it's there!

Thank you for your kind words!

 

[South Park]

I have a JTM on my build list to . You have to much tone shaping going on the gain and tone work together to keep things on the right power curve . Use the gz34 only and get some voltage sag a great sounding amp does not need mods

 

[Mcentee2]

Thanks all so far, I have to say I am bouyed up by the fact all of you are saying the same thing, that's a rarity on forums

It also makes my build process a lot easier, and I have more belief I will end up with a great sounding amp, that's or reason I picked it rather than a straight out JTM45 or a Super Lead - on paper, and listening to as much as I could find, it just seems to tick the right boxes soundwise for me.

Of course, it's not built yet, so it's a great idea at the moment still - lol !!

 

[Gene Ballzz]

Indeed - its your thread(s) that made me post here

This is the first time I have posted in Building the Classics, TBH I didn't know it existed as a forum as I usually shortcut straight to the Workbench forum, but today did a search for JTM50

Your build looks super clean and thought out

I like your above board cross wiring in black - makes it easy to see it's there!

Yes indeed, super clean build by @AndyD , all jumpers and solder connections above board for easy maintence/trouble shooting/etc! Great way to go, IMHO.

And yeah, I've just recently been fairly impressed by the seeming quality of the kits and other stuff from Modulus. In the past, I've used their chassis as has Terry Shaffer/ @Guitar-Rocker and we've been quite pleased. It's nice/interesting that at least some of their Marshall style chassis are offered in steel, as well as aluminum. I like steel! Their sourcing of transformers seems well regarded as does their other componet choices. I'm betting it will be a fun (though always too short lived) build!

I find that I enjoy monkeying around with WORKING ON guitars, amps and related gear almost as much as I enjoy playing them! On the plus side, the constant, rigorous testing of builds and mods helps keep me playing enough to keep my chops up to snuff! Each new easily obtainable sound inspires me to write new versions/combination of licks, chords, songs, etc!

Happy Buildin'
Gene

 

[Mcentee2]

Thanks Gene

The chassis is the steel version in the picklist, so this is what should come.

I chose Mallory caps as I used them in recent Supa Deluxe build and am happy with them, but also because the Sozo 0.1 were out of stock and I didn't want to mix and match; resistors are mainly carbon film with the odd composite thrown in, well that was the Supa kit anyway, CTS pots, cliff jacks; filter caps are F&T, the transformers and choke do look and feel great from a UK builder and based on originals.

All in all, really looking forward to it.

 

[Mcentee2]

Well the kit arrived this morning, really quick!

It's a lovely looking set of components, the transformers weigh a ton!

I've got the main panel bits installed now, the only puzzle I have (apart from never knowing which side of the chassis all the necessary washers go on) is how to install the pilot lamp.

Picture below, of the lamp and some sort of weird washer - no idea.

It looks like I just push it through from the front, but the hole isn't quite big enough anyway, and if I make it too big then there is nothing on the inside screwing onto it to keep it in.

And that washer, really - no idea....

Any clues anyone?

 

[neikeel]

The hole needs to be opened out just enough for the lamp to push in with almost an interference fit. Then you will note that there is a pip on the inner flange of the lamp. You need to use a fine file (or hacksaw blade) to nick the plexi panel so that the lamp slides in and the pip engages with the plexi slot. Then the washer slides over the wires inside the chassis and over the lamp body - it will only do it once reliably as they can deform. You then push the washer so that it is firmly agains the chassis inner wall. If you do it correctly the lamp sits tight on the front and because of the pip will not twist or move.
It's easy once you have done a couple.

 

[junk notes]

@neikeel or anyone else know who carries real lamps and not LED? A year ago I had to return two. I do not know how to tell the real from LED, without knowing who made it, or where it came from. Anyone who has used these in the past to repair or replace know how bright these can be..

 

[Mcentee2]

The hole needs to be opened out just enough for the lamp to push in with almost an interference fit. Then you will note that there is a pip on the inner flange of the lamp. You need to use a fine file (or hacksaw blade) to nick the plexi panel so that the lamp slides in and the pip engages with the plexi slot. Then the washer slides over the wires inside the chassis and over the lamp body - it will only do it once reliably as they can deform. You then push the washer so that it is firmly agains the chassis inner wall. If you do it correctly the lamp sits tight on the front and because of the pip will not twist or move.
It's easy once you have done a couple.

Thankyou - that all makes sense. The hole in the chassis is fine, its just the hole in the faceplate that is noticeably smaller.

I can't see anything on the outside of the casing that would be a "pip", apart from what looks like raised writing/symbols.

I'll give it a go later -can't go wrong Then onto the transformers/choke..

..and then the Cap cans..... which I think will be the next minor puzzle.

 

[neikeel]

Look on the inner flange of the square bit of the lamp - you will see it there.

 

[Gene Ballzz]

HNKD @Mcentee2 ,
Whole lotta fun to be had, although the build time is often all too short lived! Given the plastic nutted jacks supplied and the thickness of the chassis combined with front and rear panels, you may want to leave off the fiber washers inside, to allow greater thread engagement of the nuts. There is a good chance that as you have them, the threads could strip, as well as some plugs may not go all the way into the jacks properly.
Just Observin'
Gene

 

[Mcentee2]

HNKD @Mcentee2 ,
Whole lotta fun to be had, although the build time is often all too short lived! Given the plastic nutted jacks supplied and the thickness of the chassis combined with front and rear panels, you may want to leave off the fiber washers inside, to allow greater thread engagement of the nuts. There is a good chance that as you have them, the threads could strip, as well as some plugs may not go all the way into the jacks properly.
Just Observin'
Gene

As usual you are right Gene

I do indeed have some washers left from the jacks because of that !

For the pots they only came with the serrated washers this time, I just left those on the inside, but it means the outside is bare nut against the Plexi faceplate - if I did have the extra washer for external then that would make the threaded shafts too short so all in all its working out ok.