Apologies, in my earlier post by preset tonestack I meant the resistor/cap network between IC12 pins 1 & 3 not the eq later in the chain. This preset tone network is the only difference I can see between OD1 and 2. It looks like a tweaked Marshall tonestack and preset level. It would be interes...

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...

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...

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 w...

............. 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...

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 clip...

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

[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 col...

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...

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 1...

Hi Funkystrings, welcome to the thread. First off, I did not come up with all the mods myself. I found a thread somewhere, few years back, where someone made similar suggestions that ispired me to take the lid of it. I think it was the Marshall forums. (Credit where credit's due) At that time I was ...

tschrama wrote: It's a damm fine sounding preamp if you ask me

Still stock ?

Great review btw. The E530 is indeed nice. But mine developped a noise issue in the clean-high gain setting. A relay issue? I was changing tubes on the E530 and I also suddenly had a noise issue in clean high-gain. Turned out that the pins of the older tubes i had laying around, were corroded. Mayb...

........... I'd recommend Tubetinkerer head over to Merlin's Valvwizard site (excellent books!), Aiken Amps tech pages, Kevin O'Connors books are full of great info, and of course a must have is the Radiotron Designer's Handbook http://archive.org/details/RadioDesignersHandbook Thanks... will check...

I find mine cleans up pretty well on OD1 with v low gain settings, even with my overwound PAFs, just by backing off the guitar volume etc. ....................................... ....................... I'd recommend anyone who doesn't want that sound not to get one! Thx for your input, Jooshtin. I...

Well.......dunno dude.......
here's mine.... looks pretty deadcentered to me.....

That's a gross misinformation. Center-bias depends heavely on V+. Neither does center bias does automatically result in largest headroom (or lowest distorting, or highest gain for that matter, which do coincide). We do not agree, obviously. Please provide a link to prove me wrong. I don't want to b...

devastator wrote:if a proper traduction of the french document is wanted , let me know .

If you think it's useful from a technical stance (that is, not from an Audiophile POV), I would certainly be interested.

I am sorry, but to my knowledge, you are wrong on the fender bias. 100k plate and 1.5k cathode will result in a dead-center DC-bias voltage, whatever the plate-voltage. This is also the recipe for largest possible headroom. Yes, the AC-load will influence the behaviour of the stage, that's why you'd...

The cathodes are not the classical fender 1K5, because of the low V+ (160volt) in the jmp1 versus 260V in a fender*. I think marshall chose 3K for stage1 and 2k7 for stage 2, to keep the bias point, (relatively) similar to the fender bias point; which in fact is assymetrical in both the jmp1 and fe...