Marshall JMP-1 Preamp mods?

Tube or solid-state, this section goes to eleven!

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 29 Apr 2013, 21:03

damm just read it...

No, a jmp-1 will never, never sounds as good as a mesa studio preamp. Got one, worlds apart. Love my jmp-1, all in all it's a midi-controlled distortion pedal. 'Just my two favorite guitar players use one, and my dearerst CD has been recorded with one. So I love it, but it's never gonna be in the same league as a Mesa Studio. Damm that Mesa might be just the best sounding preamp ever... better than the triaxis or CAE or what not.
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby deltafred » 30 Apr 2013, 01:16

Funkystrings wrote:Sorry deltafred. It didn't look too bad in it's draft state, but when I hit post, it crunched it up even more. I totally agree. some carriage returns are needed.

That's ok, I have a short attention span and reading that was like being back at work.

Looks like a case of WYSInotWYG. :lol:
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
User avatar
deltafred
Opamp Operator
 
Posts: 1440
Joined: 06 Apr 2010, 17:16
Location: Yorkshire, England, UK
Has thanked: 370 times
Have thanks: 257 times

Re: Marshall JMP-1 Preamp mods?

Postby Funkystrings » 30 Apr 2013, 20:29

tschrama totally schooled me.... those two things I did not know. That the bass shift is pre-gain (which explains why it can flab out a bit). Also didn't know where the distortion comes from. OK, it's IC12!!, not diodes! I knew it was some solid state gizmo he he. I guess I heard "diodes" from another forum. but that's what I meant in my previous comments. I'd like to try leaving all that solid state gain stacks stock for now while running the OD 12ax7 at tad hotter without blowing the IC out. Is that even possible?

tschrama said; "Q1: more bass.. sure it can be done, but the EQ focusses the bass around (dunno) 100Hz. So upping this band, makes you loose some < 100Hz. So here the trick: keep the bass at 0 to keep the most sub-bass. Adjust mid, trbel and pres from there. Got this trick from the ADA MP-1"
Excellent info, I never thought of handling the bass that way. I'll have to try it. Cool thing about it is, even if I did mod the bass, It's always going to revert to stock w/ a "0" setting on the bass.

And you're right, the JMP-1 is like a glorified stomp box. A lot of stomp boxes are just now catching up to it these days and souning almost as good, like the Suhr Riot, some AMT products, comes to mind for one. Yeah the Mesa Studio Pre is an amazingly fat preamp. Worlds apart from the JMP-1 but this Marshall's getting better for sure!

For testing, I'm using a US strat with a 500k vol. and no tone pot, Duncan Custom shop 78 in the bridge and DiMarzio Cruzer in the neck. JMP-1 into 5150, into a 1x12 theil cab loaded w/ a WGS ET65. (plenty of bass). I'm also switching between a WGS Green Beret in an open back Vox AC15H1TV combo. For clarification, any time I say "5150", It's through one of those speakers sense that amp was voiced for greenback based speakers. I then switch between a Mesa Simul-Satalite 1x12 w/ a WGS Vetran 30 in simul-class mode, running a pair of JJ 6L6 GCs and a pair of Tung Sol EL34s. Vitage 30 based speakers (like the Vet) , in an open back 1x12 would be very lacking in bass. So if I could get that to sound good, I know I'm there. I set the JMP-1's output to Instrument level for the 5150 because that loop was designed for instrument level stomp boxes and it always sounds best that way.

I tried boosting the range of the bass with 2K2 at R177 last night, and reducing the range of the middle at R158 with 8.2 and I have to say I'm liking it a lot better. It's not a radical change either, but fuller sounding indeed!. I'm able to A/B quickly between the 5150's pre and Marshall. The Peavey still has more bass. It took a 1K8 to match the 5150's low end and to be honest, I'm torn between that and 2K2 at R177.

If I can get it sounding good between those two power amps and three speakers.... then I'm probably coming up w/ something most people would like.

These two mods are sounding good with the factory presets as well, making them fuller sounding. I'm noticing a better "feel" as well

I'm swapping back and forth, between the stock components to the new ones with alligator clips. This bass boost is not flabbing out either. It's still pretty tight.

QUESTIONS, QUESTIONS;

Previous unanswered Question; I'd like to try leaving all that solid state gain stacks stock for now while running the OD 12ax7 at tad hotter without blowing the IC out. Is that even possible?

Previous unanswered Question; Does the clean section of the JMP-1 use 100% of it's 12ax7? or is it also a solid state hybrid?

New Question 1; Has anyone here tried a bright cap mod, near the input I presume, swapping it for a lower value the way so many JCM 800 users have? And where is the bright cap located on this amp?

New Question 2; Can anyone think of a more natural way to increase the overall bass without having to mess with R177 on the eq? It's totally working sound wise, but making bass settings more touchy between numbers on the preset. (5 is much bassier then 4....
Especially if I use the 1K8 that I'm liking. I may have to stick with the 2K2 if there's no better way.

I want to Mod the Bass Shift SLIGHTLY to turn it down a tad. I'll try Tubetinkerer's suggestion next, he said; "For OD replace C116 by 47nF or smaller" That's gotta work cause I held a 47nF to it in paralell and it flabbed it out more, so that's the one to change.

This is working out well. Thanks to all!
Funkystrings
 
Posts: 5
Joined: 26 Apr 2013, 15:10
Has thanked: 3 times
Have thanks: 1 time

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 30 Apr 2013, 21:06

Funkystrings wrote:
QUESTIONS, QUESTIONS;

Previous unanswered Question; I'd like to try leaving all that solid state gain stacks stock for now while running the OD 12ax7 at tad hotter without blowing the IC out. Is that even possible?

Previous unanswered Question; Does the clean section of the JMP-1 use 100% of it's 12ax7? or is it also a solid state hybrid?

New Question 1; Has anyone here tried a bright cap mod, near the input I presume, swapping it for a lower value the way so many JCM 800 users have? And where is the bright cap located on this amp?

New Question 2; Can anyone think of a more natural way to increase the overall bass without having to mess with R177 on the eq? It's totally working sound wise, but making bass settings more touchy between numbers on the preset. (5 is much bassier then 4....
Especially if I use the 1K8 that I'm liking. I may have to stick with the 2K2 if there's no better way.

I want to Mod the Bass Shift SLIGHTLY to turn it down a tad. I'll try Tubetinkerer's suggestion next, he said; "For OD replace C116 by 47nF or smaller" That's gotta work cause I held a 47nF to it in paralell and it flabbed it out more, so that's the one to change.


Unanswered question : So all you would change is the cathode reistor ? Yes you can, without any problem. I doubt though if that would change anything, cos the tube is (IMO) in operating range and not in overdrive.

Unanswered question : The clean channel is a hybrid, but the tubes play a major role in the stages sound. The solid state only handles the CL2-filtering and the gain. The rest of the tone is created in the tubes.

Q1 : This is pretty much what tschrama did on replacing R84. C56 is the brightcap although it is preset to a fixed value

Q2 : Just a long shot ; Try bridging C121 with a bigger cap. That the highpass filter at the input that works for all channels. If that doesn't work there are options for the separate channels , but I will have to look into it.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 30 Apr 2013, 23:04

Funkystrings wrote:So my question now is this; Could I first just try boosting that 12ax7 slightly for the OD sounds? and then just lower all the gain settings in my presets? Or would that blow something out? I'd like to make the JMP-1's overdrive a little more "out of control" like the 5150, and utilize it's OD 12ax7 tube the way the infamous "fifth tube" of the 5150 did sense that's why it was put there in the first place in both amps. I just think the tube in the JMP-1 should be a bit hotter so that if the gain was maxed at 20, it would then be a little "out of control" and start hissing like a snake the way the 5150 does when maxed. thus forcing one to simply turn the gain down on the JMP-1 so that say, maybe 10 would now have the same signal to noise ratio of the stock maxed 20 setting. Just to see if some mojo happens in that 10 region. Would that be simple enough? how would you go about this?


Just put some thought to this. If you want "out of control" overdrive, forget about it. The fizz, hiss, or whatever you'd call it, is not going to happen with just one cathodefollower, which in essence is just one valve stage.
The fizz, whatever is created by distortion-chaining, actually five stages for 5150.
Just biasing the tube hotter is not going to change anything, because it is well within it's operating range and therefore not distorting. To take it into (full) distortion, you will have to increase gain of the stage by also putting
in a cathode bypass cap (I used 1 uF, but you "bassfreak" could try 22uF) which will inrease gain from 43 to 70. (not sure, but check my first post for this thread)
Stock, the output voltage at C51 is 40 * 1.8V = 72 Vtt. Pushed into full drive the output voltage will rise to 160 Vtt (=HT). That's 108 Vtt at R91 fed into IC12b which is specified at 11.2 Vtt.
Personally I would change R91/R92 just to be on the safe side.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 01 May 2013, 08:30

Tubetinkerer makes some excelent suggestions and analysis.

-Whether the OD tubes is clipping or not, is not relevant. You wont hear the clipping of the tube, because there is an element later in the signal chain that clips earlier (IC12b).

-Increasing the bass EQ, makes the bass more and more honkey, as you loose more and more deep-bass. A fixed deep-mod is possible, most practically in between IC12b and IC12c. Lot's of options there. I would suggestest a bass-boost as in the Peavey Rockmaster preamp (and maybe JSX, XXX).

-I would suggest C119 (22n) to 10-15n, and C116 (68n) to 10n-15n. This way you get a even-tighter, and normal tight sound.

-The jmp-1 OD channel has no bright cap around the gain pot. I don't know if the IC allows you to put one in.

-You can get , pretty much, as much gain as you want, but you will need more pre clipping tone shaping... more bass attenuation and prolly more trble attenuation too. maybe lower R189 (15K) to 7K5?
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 01 May 2013, 09:33

[quote="tschrama"]

-Whether the OD tubes is clipping or not, is not relevant. You wont hear the clipping of the tube, because there is an element later in the signal chain that clips earlier (IC12b).

- As with all distortion chaining you will hear the clipping. The tube distortion will color the sound one way or another. Solid state clipping induces even harmonics.
The tube can be biased to induce uneven harmonics. (See V2a in the 5150, (SLO-100, Dual Recto) although taken to extreme there)
If early clipping of IC12b would be the only sound-shaper, then the rectifier-bridge and tubestage would be pointless altogether. That's not the case.


-The jmp-1 OD channel has no bright cap around the gain pot. I don't know if the IC allows you to put one in.

-Intriquing, so I checked. The gain Pot (IC24b) is a resistor array. So I am pretty confident that you can put a bright cap either between pin 2/3 or pin 6/5.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 01 May 2013, 12:05

Tubetinkerer wrote:
-Intriquing, so I checked. The gain Pot (IC24b) is a resistor array. So I am pretty confident that you can put a bright cap either between pin 2/3 or pin 6/5.


Rechecked... only between pin 2/3
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 01 May 2013, 14:59

Tubetinkerer wrote:
tschrama wrote:
...

- As with all distortion chaining you will hear the clipping. The tube distortion will color the sound one way or another. ..... If early clipping of IC12b would be the only sound-shaper, then the rectifier-bridge and tubestage would be pointless altogether. That's not the case.

...

...
.



That's bullshit .. cann't make it any nicer..were you quoting someone?

When the first element in the signal chain is clipping, like IC12 in this case, it does so, before any of the other elements are clipping. It's clipping before the two opamps, the diode bridge, the tube stage. Once IC12 has clipped to the +v, the opamps, diode bridge, tube can do what they want, but the output of IC12 stays clippped, until input voltage drops below clipping threshold.

.. removed unrevelant words.. cann't bother to deal with 90's myths about even and odd harmonics in a preamp driven 40dB beyond headroom. Spectral analysis of the non-linear behavior of a high gain preamp is completly uselless.
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 01 May 2013, 15:34

tschrama wrote:
That's bullshit .. cann't make it any nicer..were you quoting someone?

When the first element in the signal chain is clipping, like IC12 in this case, it does so, before any of the other elements are clipping. It's clipping before the two opamps, the diode bridge, the tube stage. Once IC12 has clipped to the +v, the opamps, diode bridge, tube can do what they want, but the output of IC12 stays clippped, until input voltage drops below clipping threshold.

.. removed unrevelant words.. cann't bother to deal with 90's myths about even and odd harmonics in a preamp driven 40dB beyond headroom. Spectral analysis of the non-linear behavior of a high gain preamp is completly uselless.


Mr. tschrama you make very bold statements. Not that it impresses me, but it's challenging.
And I wasn't quoting anyone, just using my common sense.

Again we do not agree. The rectifier, opamps etc. all induce harmonics. These harmonics are superimposed on the base-signal before going through IC12. Some of these, allbeit a very small portion, will be
lower than the clipping treshold of IC12. So these will make a difference. You can argue whether you can actually hear these, but they will be there.
What you are saying is that the opamp clipping, diode rectifier and tube are just cosmetic, not contributing to the sound.
IMHO That's BS. Can't make that any nicer either.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 01 May 2013, 17:02

"Again we do not agree. The rectifier, opamps etc. all induce harmonics. These harmonics are superimposed on the base-signal before going through IC12. Some of these, allbeit a very small portion, will be
lower than the clipping treshold of IC12. So these will make a difference. You can argue whether you can actually hear these, but they will be there.
What you are saying is that the opamp clipping, diode rectifier and tube are just cosmetic, not contributing to the sound.
IMHO That's BS. Can't make that any nicer either.."


Dont mistake my bold staments for disrespect. You're a smart guy.. I think you can handle bold statements... you gotta free yourself of spectral analysis. Try to keep viewing things in the time domain and be ready to learn much more.

I never said that the opamp clipping, diode rectifier and tube are just cosmetic, not contributing to the sound... I can think of several ways they do. Again .. NOT via harmonic analysis. don't limmit yourself that way.

r,
Thijs
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby Funkystrings » 01 May 2013, 18:44

For the record, I would never want to ADD a bright cap to this preamp sense It's plenty bright already. I thought there was one in the circuit already and wanted to simply lower it's value slightly without loosing to much Marshall vibe.

Also, I have three high gain amps already, Mesa Studio pre, JMP-1, and the pre in the 5150. They all produce more gain then I would ever want, "out of control" was EVH's words in a guitar world article regarding the 5150's initial release in the early 90s and if I remember correctly, it was in context to that area between 6 and 10 on the lead gain, that even HE won't use. I do'nt even use his 5.5 setting and mostly have to reduce gain more here in Nashville at coffee shops and such, (sense this is the acoustic singer song writer capital of the world. he he he), or when I used to play in church for Micheal W Smith, I set my 5150 gain channel to about two and a half, and it still sang like a bird. So I'm not really a high gain player.

Also, I'm pretty sure you guys Engl's have the same amount of bass as my 5150's pre. the resonence on it's power amp just dials it in better to various different cabinets but it will also add's different low frequencies then the preamp bass as you increase it so if you like those, you have to reduce bass.

I know that the 12ax7 in the JMP-1 is "well within it's operating range", (even on massive gain settings like preset 00 "Smoke-em"). I'm sure we can all agree that it's ICs are thinner sounding then say, an all tube ENGL, Peavey or Mesa design but it works great for those Dave Mustaine type rhythm sounds.

Some producers will often use a tube mic pre on vocals (and I do as well in my home studio). There is a point at the beginning of the sweep of a 12ax7 that doesn't sound much different then my discreet class A mic pre, but as I increase the gain and hear it just starting to distort, I then back it off to that point where it's just starting to bite, and it will make an otherwise lifeless vocal come alive without a lot of board eq. For now I'll just call it an "on the brink sound".

On a tube mic pre, when it's starting to bite like that, it also adds a tiny, tiny bit of hiss at the expense of the much better vocal sound. So if I can get it to bite on the JMP-1, I'll just reduce gain at the front control panel so that any hiss would be dialed away.

I think the 5150 has this approach more dialed in, as others have driven that effects return just a little too much and thought the power amp was clipping (The 5th tube is post FX return), and Eddy said it was there to "further warm the sound" so I'll call it a better "on the brink" setting that I'm hearing in the JMP-1. I just want to do a very simple experiment to see if I can hear it on the JMP-1's tube. I'll know it if I hear it. I'm not trying to " bring it into (full) distortion", as you mentioned, I'm thinking I shouldn't need a cathode bypass cap for this, but if you could suggest some subtle component values for that, I may give that a try as well later down the road.

It should be a very minimal mod to try and get that tube to "bite" more without changing the amp to much at all. The JMP-1 will always be a high gain, solid state beast though. I want to see if I can fatten it ever so slightly without an extensive mod, by going with the nearest component value change at the cathode resister, I guess . If I like it, I'll keep it, if not, I'll put it back.

So which one is the cathode resister again? and what direction should I change it's value?
Funkystrings
 
Posts: 5
Joined: 26 Apr 2013, 15:10
Has thanked: 3 times
Have thanks: 1 time

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 01 May 2013, 19:05

Tried to find a way to explain it in simple terms...

Before the first element start clipping, all the previous elements in the signal chain are in still their linear regeon, often by a very large margin. Beyond that point, the clipping element is unable to pass information about the nonlinear behavior of previous elements.
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 01 May 2013, 19:59

Funkystrings wrote:
So which one is the cathode resister again? and what direction should I change it's value?


R124 .. as tubethinkerer said.. piggyback a 680nF, 1uF-- up to 10uF on top of it.. bit more gain.. bit more bite and tighness with lower value caps.

I would add a 1uF across r124, 470pF across r126. Now the pre clip voicing is very similar to an E530. No.. it won't sound the same.. but it will have some similarity.
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office

For this message the author tschrama has received thanks:
Funkystrings (02 May 2013, 01:06)
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 02 May 2013, 08:07

tschrama wrote:
............. you gotta free yourself of spectral analysis. Try to keep viewing things in the time domain and be ready to learn much more.
..................... Again .. NOT via harmonic analysis. don't limmit yourself that way.


I'd like some explanation on this, before I just take your word for it.
You are not taking this into the Audiophile realm, are you ? "Measuring means nothing. Trust only your ears and spooky theories", that kind of stuff ? "Polish your tubes for crystal clear sound" ?

As far as I understand, every distortion stage creates harmonics from sound (base signal + induced harmonics) created by a previous distortion stage. At the end of the chain pretty much all the original signal will have been
transformed into a mush of harmonics that makes up the eventual sound. The more stages => the more high frequency harmonics (5th stage hiss, fizz, outtacontrol... )

Q: What has the time domain got to do with anything ? (Quantum mechanics :-? Parrallel sonic universes ? 6-string theory ? Uncertainty principle ? )
Q: In what way is harmonic analysis "limitting yourself" ?

Enlighten me, please.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 02 May 2013, 08:29

Funkystrings wrote:Also, I have three high gain amps already, Mesa Studio pre, JMP-1, and the pre in the 5150. They all produce more gain then I would ever want, "out of control" was EVH's words in a guitar world article regarding the 5150's initial release in the early 90s and if I remember correctly, it was in context to that area between 6 and 10 on the lead gain, that even HE won't use. I do'nt even use his 5.5 setting and mostly have to reduce gain more here in Nashville at coffee shops and such, (sense this is the acoustic singer song writer capital of the world. he he he), or when I used to play in church for Micheal W Smith, I set my 5150 gain channel to about two and a half, and it still sang like a bird. So I'm not really a high gain player.

Also, I'm pretty sure you guys Engl's have the same amount of bass as my 5150's pre. the resonence on it's power amp just dials it in better to various different cabinets but it will also add's different low frequencies then the preamp bass as you increase it so if you like those, you have to reduce bass.


I don't know 5150 personally, but only from what I've read or have been told. But Engl E530 has very little bass. Which is fine for tight high-gain riffing. But since I am not a high-gain player myself either
I have modded it to my liking, balancing the bass out a bit more.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby Jooshtin » 04 May 2013, 17:49

Here's a jmp-1 waveform chart from the service manual, got it off the web ages ago and forgot I had it…

Image

Just a thought for a mod, you could replace R122 & R121 between IC12 pins 2 & 5 with a tonestack using trimmers like in the Dumble HRMs. A dual rectifier tonestack could drop in there nicely for a contrast. I did this just as an experiment in a Musicman amp I've got (FMV tonestack) and it works really well:

Image

Cheers Tubetinkerer for sharing your mods and ideas, they have got me thinking, and made me want to have a look at the clean channel sometime (you weren't wrong about the biasing etc earlier either… :wink: ). I've just noticed you said your jmp-1 has a lack of range in the tone controls and sparkle in the cleans, usually these have loads of eq available, mine can get way too bright at extreme settings. What amp/speakers are you running it through? Are you using the line outs and not the emulated speaker outs into the amp?

I may try tweaking R142 to reduce the overall gain slightly. However, I find mine sounds superb and gets used loads in the studio, and bizarrely often sounds more "hot-tubey" than some expensive rigs - for clients who want that Marshall sound. Don't underestimate the effect of the power amp/speakers/cabs on the tone. Mine is run through a 9005 all tube power amp (recapped, microphonic ceramic caps in signal path replaced, and biased nicely) into a couple of custom closed back 1x12 cabs (Eminence Wizard & Governor speakers). It gets put in the live room and cranked up loud :D Also gets used a lot for bi-amping bass too.

IMHO the jmp-1 is the natural progression from the DRP-1, 9001, 9004 preamps - alongside the JCM900. Remember too that when the jmp-1s were designed a lot of UK manufacturers were having a hard time getting decent tubes, so it's no surprise that the OD channel doesn't rely on the tubes for clipping - it does of course add to the tone/mojo and the cathode follower sets the impedance into the OD1 preset marshall tonestack etc.

Hmmm... :hmmm:

Tschrama wrote: ".. all above post IMHO are worthless, including the French article. That guy is hopelessly lost about what's actually going on in the JMP1."

You sure about that? With respect, you are simply wrong sir. He's not trying to make it into something it isn't, he starts with the premise that it is already a great sounding preamp. OK, I wouldn't bother replacing the ICs, but probably the most popular mod, of any worth, I'm aware of is replacing microphonic/bad sounding capacitors in the signal path and re-capping the power supply. Done to improve the reliability and consistency of rigs that gig regularly and don't live in the bedroom. There's a lot of touring/recording racks that still have one or two jmp-1s in them…

Here's a nice quote, in relation to tube stages in this universe… "The larger the audio signal is, the more of the load line the operating point moves over and so the greater the distortion, and in most triodes the harmonic distortion is directly proportional to signal level. If multiple gain stages are cascaded then each will add another layer of distortion on top of the last, progressively building up a thicker tone by increasing the number and amplitude of harmonics." Merlin Blencowe, Preamp book, 2nd Ed.

Harmonic distortion, intermodulation distortion, tone shaping, cut off clipping, grid current clipping, biasing and anode load resistance etc. all have an influence on the resulting sound in a tube amp. Marshall, Fender, Mesa et al are not known to use any components that they could possibly save money with by leaving out!

For this message the author Jooshtin has received thanks:
tschrama (04 May 2013, 20:18)
User avatar
Jooshtin
 
Posts: 28
Joined: 31 Mar 2011, 20:18
Location: Luton, UK
Has thanked: 39 times
Have thanks: 13 times

Re: Marshall JMP-1 Preamp mods?

Postby tschrama » 04 May 2013, 20:32

Voltage chart is great,thx! Where did you get that? Is there a service manual out there?

but you guys make me so tired..*Merlin Blencowe.. useless quote ...great example of a book with a fundamental error on each or every other page. *I am not going to repeat myself on the harmonic distortion myth. .. * Centre biasing can be interpreted in two ways.. at least I took the trouble to clear that up. Centre grid biasing is not automatically achived by using 1k5 cathodes and 100K anodes; it gets you in the ballpark, but depends on HT and load... *Just because I claim that a clipping stage cannot transmit any information about the behavior of it's pervious stages during that clipping transient, doesn't mean that I claim Fender, marshall etc are using useless components. * The jmp-1 OD CF is not driving the tonestack, nor does the output impedance of a CF have a mojor effect on a tonestack.. (and did you knwo that the bias point of the CF does have a mojor influence on the TS behavior?) ..EDIT..sigh..

Now let's talk JMP1 mods:
Adding an 47K tonestack for the OD2 channel... nice 8)

Does anybody know why the OD1 channel seems to have less gain than the OD2 channel? Or is that just something achived digitally?
Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. US Copyright Office
User avatar
tschrama
Breadboard Brother
 
Posts: 118
Joined: 17 Aug 2008, 09:39
Has thanked: 20 times
Have thanks: 6 times

Re: Marshall JMP-1 Preamp mods?

Postby Tubetinkerer » 06 May 2013, 15:16

tschrama, it's dawning on me that we are not on the same page in respect to "harmonic"

Did you understand that I (or anyone else) was not referring to "harmonic distortion" in any way, where it comes to clipping distortion ?
I assume you know that harmonic distortion (THD) refers to the non-linearity of the transfer characteristic of the amplifying stage (tube/transistor etc.),
whereas I was merely stating that clipping distortion causes harmonics (overtones) to be generated, and imposed/added to the base signal.

So when it comes to harmonic dstortion, I agree with you, but this is not an issue here, since in guitar amplification it's good practice to take advantage of the non-linear transfer.

I suppose you are mixing the separate meanings of "harmonic" in the discussion.
User avatar
Tubetinkerer
 
Posts: 28
Joined: 30 Mar 2013, 13:55
Location: Netherlands
Has thanked: 1 time
Have thanks: 2 times

Re: Marshall JMP-1 Preamp mods?

Postby MoonWatcher » 06 May 2013, 17:47

If he's still using them (don't know why he wouldn't be), it would be cool to know what mods were done to Janick Gers' JMP-1's. It's a nice cross between classic and modern, although that could come down to some of his other gear, but he doesn't seem to run half the crap that Dave or Adrian do.

...There's this cool "hollow knock" to his sound as well - something I would never associate with that pre.

But it's all just speculation as to what could have possibly been done.

Edit - scratch that. Gers is the only one of the three that's using an old Mesa Studio pre to go with the JMP's, which I'm guessing are used for either cleans or "buzzier" stuff (the JMP's and not the Mesa pre).

It looks like both Dave and Adrian are now using JMP-1's exclusively as pre's, driven into Marshall heads set for clean power amp operation only. Dave's sound is a bit buzzier than in years past, but I chalked that up to the use of those G12T-75's and the DSL/TSL heads. Adrian's sound is usually a little warmer, but he's been pushing stuff thru TS's for years, so there's the midrange thing.

I guess they've been doing the same sort of thing for so long that they just want it midi/automated as much as possible. I think Piece of Mind had some of the best guitar tones on it, truth be told. I think they went into the Nassau studios with the "then new" 2203 version of the JCM800's. Not much clean stuff on those old Maiden tunes, though.

Sorry for the big digression, but this thread almost needs it... :blackeye
MoonWatcher
Diode Debunker
 
Posts: 718
Joined: 28 Jul 2008, 13:27
Has thanked: 42 times
Have thanks: 63 times

PreviousNext

Return to Amplifiers

Who is online

Users browsing this forum: No registered users and 9 guests