Marshall JMP Master Volume 20W Build

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Littlewyan
Posts: 1911
Joined: Thu Sep 12, 2013 6:50 pm
Location: UK

Re: Marshall JMP Master Volume 20W Build

Post by Littlewyan »

Yes it seems that a lot of Marshalls from the 70s get ripped apart. Quite often the ones you see on Ebay have bullet holes in them.

How big are these practice rooms? The ones I use aren't huge so a 50W amp cranked up is ear blistering and almost unbearable, even with ear plugs. Also I live in England, its a bit cramped over here compared to America so you can't make as much noise!

Cool amp! and cool collection! I've toyed with the idea of a Hiwatt but I think I'm more at home with Marshalls.

Thank you Deeder
gldtp99
Posts: 226
Joined: Wed Jan 03, 2007 9:21 am
Location: N. Texas

Re: Marshall JMP Master Volume 20W Build

Post by gldtp99 »

Yes, many of the '70's and 80's Marshalls have been modded----- now that the original condition amps are getting to be worth some good money it seems a shame ---- I no longer want to contribute to the molestation of original Marshalls but if one comes to me already molested (with extra holes drilled,etc) and the owner wants a particular tone i'll usually take on the project and build modded circuits.
Here's a link to the rehearsal building I'm in currently----- room sizes and rates/availability:

http://www.universalrehearsalarlington. ... -and-rates

Here's a 1981 Marshall 2204 that I own that is in stock condition-----some parts have been changed but it is still the stock circuit and has never been modded---- I'll keep this one stock:

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%202204%201981/IMG_5034_zps0bbe3b27.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%202204%201981/IMG_5033_zps9a1c8e9f.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%202204%201981/IMG_5030_zps0cfa0e81.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%202204%201981/IMG_5029_zps906513d5.jpg[/img]

A customer brought me a modded JMP Superlead that had stopped working--- here are "before" pics of the modded orig PCB before I took on the rebuild job:

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_4994_zpsc9d7dfff.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_4995_zpse9700994.jpg[/img]

The closer I looked at this amp, the less I could believe that it ever worked at all with these "mods"---- or why it didn't start on fire.
He wanted a "Hard Rock Marshall without Pedals".
So I rebuilt it into this:
[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_5008_zps130e4ec0.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_5007_zpsa45f7940.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_5009_zpsd44d211b.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_5001_zps4b396087.jpg[/img]

[IMG:800:600]http://i46.photobucket.com/albums/f112/gldtp99/Marshall%20SL%201979%20Vlad/IMG_4999_zpsf7c11ada.jpg[/img]

Here's a poor quality clip of another player (he plays Grindcore style) trying it out in my shop before the owner picked it up:

https://youtu.be/zog4b7jkq74

This was done several yrs ago and the owner is still using this one as his main stage amp---- I talked to him on the phone last night---- he brought me other Marshall JCM 800 2203 amps and I did much less invasive (and reversible) #34 Mods on them.
The big amp users here don't always play that loud (some do play very loud)----- a 50 watt 2204 would easily produce enough volume but their point is the extra power allows very low guitar tuning (sometimes 8 string guitars) so the lowest freq passages have a good, tight tone----- a 2204 doesn't do well when faced with this task----- and they're become accustomed to the feel and dynamics of high wattage guitar amps, so that's what they want.

Here's a poor quality clip (with low vol again) of a friend playing his 8 string guitar through my 150 watt Channel Switcher prototype------ most of what he's playing is much lower than a normal guitar range:

https://youtu.be/9Rk6EBfB2lw
'
Wes is playing the 8 string in my shop---- one of his bands, "Primordius"--- is on tour right now in Western Europe: https://www.facebook.com/PrimordiusTXDM/?pnref=lhc

No UK dates on their schedule, sorry.

So their use of very big amps often has more to do with note fidelity of the lowest freq passages rather than the ability to knock down walls with volume----- but the temptation to turn it up and blast away is always there so loud playing does happen in many bands.
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Littlewyan
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Location: UK

Re: Marshall JMP Master Volume 20W Build

Post by Littlewyan »

I wish I had rehearsal rooms like that near me! Good idea charging a monthly rate.

Thats a very good example of a 2204. You don't see many of those come up for sale, its mostly the 2203 100W Heads. Thats the case over here anyway.

The JMP Superlead has been destroyed! Who on earth modified that?! You did a pretty good job at clearing it up and it sounds great!

I know what you mean about the higher power amps having more bass. I have always noticed that lower power amps have a harder time with bass notes compared to higher power amps. Even when I attenuate my Marshall down to the same level as my 6V6 Amp I notice it has a more powerful bottom end.
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Littlewyan
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Re: Marshall JMP Master Volume 20W Build

Post by Littlewyan »

I have finally done a recording of the amp!

The first part is with the master up as I would normally play it and the last bit (there is a 3/4 second pause) is with the master down.

First part:

Presence: 5
Bass: 5
Middle: 7.5
Treble: 7
Master: 8
Pre Amp: 8


Second Part:

Presence: 5
Bass: 5
Middle: 7.5
Treble: 7
Master: 2
Pre Amp: 8

I recorded it using my Focusrite Scarlett 2i2, line out from my attenuator into that and then a cabinet sim on the PC.
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gldtp99
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Location: N. Texas

Re: Marshall JMP Master Volume 20W Build

Post by gldtp99 »

Amp sounds great !!! "Rosie" sounds good to me pretty much every time.

I don't want to post the guy's name that modded (butchered) that JMP Superlead------ he's a local here in N. Texas and we have mutual friends but I don't know him personally---- I've seen other amps that he's done and I've been impressed not at all---- I re-worked another he'd done but it wasn't as messed up as the one I posted pics of.

I like my JMP 2204---- it had physical damage when I first got it----- one of the filter caps was broken off, the amp was loose in the head cab and the front panel of the head cab was bashed in, and no logo.
Some repairs and it's been good to go for several years.

I decided to take over a build (low voltage 2204 clone, EL34x2) that I had been doing to teach a friend "how to build amps"------ it's been sitting for too long unattended so I'll finish it up as I can get to it. I could try some JJ 6V6's in this one just to see how they sound.
I'm trying 120k plate load resistors on V1 and an altered Voltage Divider (stock 470k/470k------ i'm going with 470k ground/330k series with stock 470pF second Treble Peaker cap)----- also a .68 booster cap on V2a.
Not sure yet what I'll do with the Cold Clipper----- might stay with the stock 10k.
We'll see how it sounds and go from there............... gldtp99
joeboo88
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Location: Way up North

Re: Marshall JMP Master Volume 20W Build

Post by joeboo88 »

Nice sound Ryan!
great job on the amp
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Littlewyan
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Re: Marshall JMP Master Volume 20W Build

Post by Littlewyan »

Thanks man! Can't beat a bit of Rosie ;).

Ah well thats fair enough, it is a shame that his standard of work isn't so great though.

How do people let amps get like that?!

Thats going to be a meaty amp! I've thought about fitting a switch onto my amp that will add in a .68uF Cap on V2A and also lower the Cold Clipper to 8.2K or something. Then another switch that will make the cold clipper 2.7K/.68uF to make it more of a non master volume amp when plugged into the low channel, as at the moment I don't use that channel at all!

Thanks joeboo :)
sturgeo
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Re: Marshall JMP Master Volume 20W Build

Post by sturgeo »

I think I might have to build something along these lines, my JTM45 build is just to clean at normal volumes and I don't want to start adding cathode bypass caps and changing the NFB resistor etc as that'll take the amp away from what it was built for and having another new amp is always better :D

I better get the PT ordered pronto as the PTs I get from ampmaker are normally Danbury models and IIRC they've closed shop :cry:
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Littlewyan
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Re: Marshall JMP Master Volume 20W Build

Post by Littlewyan »

What level of gain are you looking for? The 2203/2204 amps don't have that much gain with the master volume turned down low. You could increase it by modifying the preamp but obviously it won't be a 70s Master Volume Pre Amp anymore. Or do you think you can cope with 20W? Its only 3dB quieter than 50W bear in mind.
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M Fowler
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Re: Marshall JMP Master Volume 20W Build

Post by M Fowler »

What transformers are you using for the 150w Mule?

Mark
gldtp99
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Re: Marshall JMP Master Volume 20W Build

Post by gldtp99 »

M Fowler wrote: Thu Mar 23, 2017 7:06 pm What transformers are you using for the 150w Mule?

Mark
The PT is a Heyboer custom wind----- I had four of these PT's wound with massive capacity with the intent of building big amps for the local metal players----- 450V B+----- the OT is the big 100 watt rated one from Classictone: http://www.classictone.net/40-18072.html

This OT has a 2.2k primary which is a bit high for six 6L6GC's but I built up this channel switcher experiment with iron that I had on hand---- I experimented with pulling two 6L6's and running the amp on only four (sounded good) and found that I much preferred the thicker tone of all six 6L6GC's.
I have a Heyboer Hiwatt Partridge clone 100 watt OT on hand that has a 1.7k primary that I'm thinking of using whenever I get around to building another one of these------ this OT is also an extended bandwidth type of OT, compared to most guitar amp OT's, so I'm thinking it will work well and present less load to six 6L6GC's than the Classictone with a 2.2k primary.
I realize that Heyboer would happily wind me OT's to whatever spec I wanted----- but I'm not sure how far down the rabbit hole I want to go with these huge six output tube amps.
I have another single channel KT88x4 version of the similar preamp that I built into a Metro 100 watt MV kit amp---- using the Metro/Heyboer kit iron with doubled first filtering stage values----- has Metro FX Loop and switchable bright cap------ this one has plenty of power and sounds very good so I'm still undecided about further experiments with the six 6L6GC idea.
The six 6L6GC idea came from my experience with Sound City 120's with six EL34's---- I also built one of these SC 120's up with a version of the 5 stage preamp (single channel only)---- It was bought by a local studio owner/metal player and he's been rehearsing/recording/gigging with it for some time now------ plenty of power in this one, too.
These players don't usually play extremely loud but want a very powerful amp so it will handle the very low guitar notes, with decent fidelity, that their music styles contain.
I'm finding that the stock Marshall type pre-PI Master Vol works very well with this circuit so there's no need for anything fancy------ simple is good................... gldtp99

PS---- my real first name is Mark, too----- I think i'll stick with gldtp99 or it could get confusing around here----- years ago on another forum some people confused me with Mark Huss because I was doing a lot of Hiwatt clones and Sound City 120/Hiwatt conversions at the time.
Then there is Mark Cameron.......................lots of Marks building amps :lol: :lol:
sturgeo
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Re: Marshall JMP Master Volume 20W Build

Post by sturgeo »

Littlewyan wrote: Thu Mar 23, 2017 2:02 pm What level of gain are you looking for? The 2203/2204 amps don't have that much gain with the master volume turned down low. You could increase it by modifying the preamp but obviously it won't be a 70s Master Volume Pre Amp anymore. Or do you think you can cope with 20W? Its only 3dB quieter than 50W bear in mind.
A reasonable amount, not high though like a modern amp. The preamp is going to get some of the typical mods, switchable 0.68uF bypass on V2b, V1b is getting a 3 way toggle with one side being just a bypass cap and the other being a lower value cathode resistor & cap. I'll probably leave the default as 10k to start with.

I'm interested in your power section, seems a little different to the normal 2204 layout :?

Edit: Just released its a non CT secondary, this calls for coffee and more sleep.
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M Fowler
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Re: Marshall JMP Master Volume 20W Build

Post by M Fowler »

Mark (gldtp99) thanks for your response. I've been using those Large Hammond 378CX PT and 1650TA OT for four KT88 bass amps.

Damn large transformers.
gldtp99
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Re: Marshall JMP Master Volume 20W Build

Post by gldtp99 »

M Fowler wrote: Fri Mar 24, 2017 7:42 pm Mark (gldtp99) thanks for your response. I've been using those Large Hammond 378CX PT and 1650TA OT for four KT88 bass amps.

Damn large transformers.

Big iron from Canada !! Nothing wrong with that !!

So you're building KT88x4 bass amps ? Your own circuit design or adapted from an existing amp ?
I'm in the (slow) process of building a Marshall Superbass preamp into yet another Sound City 120 for our bass player----- right now we're using my 1973 Marshall Superlead as a bass head thru a 1x15 cab and a 4x10 cab------ the Superlead, with Vols at @4-6, is sounding very good and we're thinking the Superbass circuit thru the SC 120's EL34x6 and bigger iron should also be a good sound---- the bass player needs a back-up head so the better sounding one will be the regular head and the other will be the back-up.
We've tried out my 1972 Hiwatt DR103, a DR103 clone I built, Fender BF Showman, two 70's Ampeg V4B's and the 1973 Marshall Superlead just works best as a bass head in our situation. It seems to crunch at just the right spots for what we're doing.
We're tuned to C# Standard and are playing modern type Alt/Sludge original music----- I've got plenty of time to build this SC 120/Superbass because I've put the band on hold until I retire from my regular job later this year----- I have no time for any fun right now with the massive overtime schedule we're working. I've closed my amp shop until then, also.
I'm playing thru my 150 watt channel switcher prototype running a 90's RI Orange 4x12 cab------ the young people i'm playing with don't seem to mind playing with an old guy like me------ the bass player and drummer are both young enough to be my children and are talented players------- this should be a fun project................ gldtp99
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M Fowler
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Re: Marshall JMP Master Volume 20W Build

Post by M Fowler »

Nice that you will be able to retire and get moving on your amp projects, can't wait to see what you do.

I built #1 150w bass head based on the preamp of the Fender Bassman 100 controls into modified PI for KT88's

The #2 bass head was based on Mojotone's 50w Bass head preamp into the modified PI for KT88's. The mojotone preamp has mid shift knob.

Both amps were just an experiment to replace the broken down terrible Ampeg SVT's the local bass players had. I hate working on SVT's.

Mark
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