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If you want to share the technical details and drawings for the mod, then you are in the right forum section and please do share it. :)
 

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It's generally a simple matter of either lifting the ground connection of the midrange pot, or inserting a large-enough resistance in series with it. My info says the Midrange control is a 25K pot. If you stuck 100k between ground and the ground connection to that pot, that would likely provide enough isolation.

The Marshall/Fender tonestack selectively bleeds signal to ground. If you make that path to ground more resistance, there is less bleed. The treble boost will still work pretty much the same, but the bass and mid controls will have a much less noticeable effect.

I did this mod to my old Blackface Tremolux head 30 odd years ago, after reading an article outlining it in a 1981 issue of Polyphony magazine. The result is a useful level boost, since you're not bleeding off as much signal. The lift also provides more "heft" to the signal, in the absence of as much bass and mid loss.

Ideally, one would use a pot or trimmer to adjust how much additional resistance to ground from the midrange pot suits you. A remote footswitch could then be used to simply bridge the added resistance and go back to normal tonestack functioning. It will work for anything using a Fender-type tonestack. Note that in some amps, there IS no Midrange control, simply a fixed resistor to ground where a Midrange pot might normally be. It works the same way. Just either break the ground connection of that resistor, or insert some other resistance in series with it.

I should clarify that the mod does not affect gain at all. However, if there are any gain stages in an amp, subsequent to the tonestack, you will be hitting them with a hotter signal, so some mild overdrive is a definite likelihood
 

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Just a quick addendum. Get hold of the Duncan Tonestack Calculator ( TSC ). It lets you do instant graphing of the frequency-response changes of different component values for a variety of tonestacks, including Marshall. If I stick 100k in series with the ground side of the Midrange pot, I get an overall boost of several DB and a boost of about 6db for the mids and upper bass.

Fun and useful to play with.
 

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Discussion Starter #6
Just a quick addendum. Get hold of the Duncan Tonestack Calculator ( TSC ). It lets you do instant graphing of the frequency-response changes of different component values for a variety of tonestacks, including Marshall. If I stick 100k in series with the ground side of the Midrange pot, I get an overall boost of several DB and a boost of about 6db for the mids and upper bass.

Fun and useful to play with.
Thank you for the cool info.
I kinda like it better with the lift mod. It is a little brighter and gainy. The mids are really honking and what I like most is the feel. Great string attack.
I think it would work best with a footswicth on/off as a solo boost for live playing.
 

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That's how I set up my old Tremolux head. Since the tremolo was cancelled with a connection to ground, I simply subbed a stereo jack for the existing mono jack on the back of the head, using one ground connection for the tremolo, and the other for engaging/disengaging the mid-lift.

I'll see if I can scan the article and post it, although it won't necessarily tell you more than I already have.
 

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I'm sorry I don't have any schematics of my mods.
But thank you for your interest.
Of course you have schematics, all builders and modders do. Why don't you just say you prefer not to share it?

I've used this circuit on my amps for years. You just lift the tone stack above ground with a fixed or variable resistor.
 

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I'm sorry I don't have any schematics of my mods.
But thank you for your interest.
Other commercial operators on this forum keep their advertising and promotion in the commercial area.
It's not really fair to them that you do not play by the same rules.
 

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Discussion Starter #10
I'm very sorry to make members angry and upset. The post was not intended for advertising and promotion of my Plexi R/T mod.
It was just for a discussion on the Tone Stack Lift mod.
My apologies, I won't post on this forum anymore.
Goodbye!!
 

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Don't go away. And certainly don't go away mad.

It's a fine line to walk between discussing something one is simply interested in, and discussing something one is interested in and makes a business out of. Sometimes it's simply a matter of choosing the right words. "My mods" starts to have the flavour of advertising a product or commercial service. And as jb noted, it's better if anything promoting one's own business be confined to those subforums here where it's supposed to go, and keep all the other subfora for discussing gear. That's all. No big whoop.

BTW, there is nothing that stops anyone here from asking "Does anyone know where I could get X done to my amp?", and another member pipes in "You could try so-and-so in Collingwood". Friendly referral advice is entirely legit.
 
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