Lee Jackson mod

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awangotango
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Post by awangotango » Thu Dec 21, 2006 2:58 pm

the difference with this mod is that V1 is not cascaded, but rather left stock and half is still used for the normal channel like stock non-master amps. Lot's of preamp gain mods cascade one half of V1 into the other if i'm not mistaken, as did the late 70's jmp's and then the jcm 800, and also the 'SIR' mod and others. This Lee mod instead, add's a gain stage later in the preamp which i assume creates it's own type of effects on the gain and crunch. My hope is that is doesn't create extra distortion, but just gives some texture and sustain to the preamp. The result i hope is that more of the plexi feel remains, rather than the amp becoming a jcm800 type gain. I'm currently working on getting this into a stock '68 superlead spec amp to give it a test drive. It appears to be a simple mod but tricky to get it looking clean in terms of wiring and layout. A new pre socket is drilled and V1 and V2 wiring are moved over one space to their new locations, with the new gain stage tube added after V2 (in original V2's location).... instead of hacking in a tube between the existing pre-sockets.

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Tone Slinger
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Post by Tone Slinger » Fri Dec 22, 2006 10:10 pm

Where are the caps and resistors gonna be located for this 4th tube ? It will be a small separate board ?

awangotango
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Post by awangotango » Sat Dec 23, 2006 12:57 pm

You only need one added turret to hold the other leg of .68 cap. Tried the mod (as detailed by cameron) last night at rehearsal. It did what i expected and had the crunch. Sounded very much like the Dave Prichard tone which i can now confirm, that was the mod he used. Unfortunately, it is alot of extra gain from the stock superlead circuit. I may try a 12at7 or lower gain tube for the new gain stage to see if i can get the crunch without all the extra gain and saturation. It's a great mod though and doesn't sound like other master volumes (ppimv or the jcm800 type masters). It is super heavy, full and meaty sounding with no fizz or odd noises. Overall, I wish i could get the extra crunch without the gain, since for whatever reason, whether it be my playing style or pick attack, i get plenty of juice from a stock circuit and don't need all the extra from this added tube. Very cool mod though. Also reminded me of Lynch's 'back for the attack' tone, so for anyone in an 80's cover band, this would be a mod to try. My 80's tastes run more toward the early 80's and the holdover from the NWOBHM so this mod can be a little too much gain and not enough 'cut' for that. My merc Ot may also not be the right match though, since it is very middy and warm without alot of cut. I can imagine this being a great mod with a stock metal panel, stock dagnal amp for sure though.

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Guitar Adjuster
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Post by Guitar Adjuster » Sat Dec 23, 2006 3:26 pm

awangotango wrote:You only need one added turret to hold the other leg of .68 cap. Tried the mod (as detailed by cameron) last night at rehearsal. It did what i expected and had the crunch. Sounded very much like the Dave Prichard tone which i can now confirm, that was the mod he used. Unfortunately, it is alot of extra gain from the stock superlead circuit. I may try a 12at7 or lower gain tube for the new gain stage to see if i can get the crunch without all the extra gain and saturation. It's a great mod though and doesn't sound like other master volumes (ppimv or the jcm800 type masters). It is super heavy, full and meaty sounding with no fizz or odd noises. Overall, I wish i could get the extra crunch without the gain, since for whatever reason, whether it be my playing style or pick attack, i get plenty of juice from a stock circuit and don't need all the extra from this added tube. Very cool mod though. Also reminded me of Lynch's 'back for the attack' tone, so for anyone in an 80's cover band, this would be a mod to try. My 80's tastes run more toward the early 80's and the holdover from the NWOBHM so this mod can be a little too much gain and not enough 'cut' for that. My merc Ot may also not be the right match though, since it is very middy and warm without alot of cut. I can imagine this being a great mod with a stock metal panel, stock dagnal amp for sure though.
Great,

Glad it worked out. Let us know if the 12at7 lowers the gain..

Allen

awangotango
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Post by awangotango » Sat Dec 23, 2006 5:22 pm

I think the 75Watt celestions (or 65's) are a great match for this mod. With a stock superlead, they are thin and compressed with no mids, but because this mod is so bulky and chunky in the mids, the 75's would be nice match and keep things clear and tight. The cab I used to test out this mod is my pulsonic 03 cones 25W M cab. There was a 75 loaded cab sitting right there in the rehearsal space. I didn't even think to plug into it at the time. Maybe next time.

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davyped
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Post by davyped » Sat Dec 23, 2006 6:19 pm

Any clips?


Dave

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Post by vkaxeman » Sun Dec 24, 2006 11:40 pm

Are the Lee Jackson DVD's useful for a newbie and worth the $ he is asking for them?

http://leejackson.com/MasterSeries/Mast ... chase.html

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5150loveeddie
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Post by 5150loveeddie » Tue Jan 09, 2007 12:35 am

So can someone resume what it is the mod(s) exacly in one post?? Guitar Adjuster?? I think I saw a .001uf cap somewhere on a LJ amp??

Thanks again guys!!!
Glutathione increase specialist

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rockstah
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Post by rockstah » Tue Jan 09, 2007 2:35 am

Guitar Adjuster wrote:Here is a layout for a 4th preamp tube circuit for a 2203 MV amp, by backing off the gain and cranking up the master you can get that Plexi crunch with EL34's but you have to have 69 spec filtering, the lower 12xxx filtering does not work so well with the added gain.

Allen
is the " Allenpreamp 2203 circuit.jpg" the lee jackson mod?

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Post by SDM » Tue Jan 09, 2007 4:44 am

rockstah wrote: is the " Allenpreamp 2203 circuit.jpg" the lee jackson mod?
Not the same mod.

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rockstah
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Post by rockstah » Tue Jan 09, 2007 12:17 pm

heya Steve- happy new year - so then which mod is this? :)
Mark

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Post by Necrovore » Tue Jan 09, 2007 3:51 pm

Mark if you can wait til after 6 I can email you a scan of the schematic. Unless Allen beats me to it.

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rockstah
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Post by rockstah » Tue Jan 09, 2007 4:21 pm

excellent! :)

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Guitar Adjuster
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Post by Guitar Adjuster » Tue Jan 09, 2007 5:00 pm

rockstah wrote:
Guitar Adjuster wrote:Here is a layout for a 4th preamp tube circuit for a 2203 MV amp, by backing off the gain and cranking up the master you can get that Plexi crunch with EL34's but you have to have 69 spec filtering, the lower 12xxx filtering does not work so well with the added gain.

Allen
is the " Allenpreamp 2203 circuit.jpg" the lee jackson mod?
E-mail sent Mark.

Allen

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rockstah
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Post by rockstah » Tue Jan 09, 2007 5:33 pm

thank you Allen!

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