LEE JACKSON GP-1000 88 replica for sale

[Rune]

Yes, we kind of solved the noise issue(s) by moving almost all the V2 components to tube PCB. Tried it on my clone as well, turns out the pot, which also was a problem on the prototype is wired wrong or just defective. Have to wait and see what TWCC has to say about it, but he's super busy as usual and have no time answering emails or testing with the project. I'm almost pleased with the sound. I think AYDY is totally nailed now, well almost, gorhrut still uses a trim-pot instead of diodes and resistor, but basically it does the same thing, and only slightly changes the sound.

Also, if you have a Fender Concert II you basically have the GP-1000, only need to change 6-8 parts and add diodes. Lee Jackson stole Fenders idea after working for them in the mid 80's. There is very little Marshall about any of the original versions. Clone resembles it more, but is more like a Mesa Boogie 2C specs-wise.

I might still send my original 88' to the Bodom tech, would be fun to see what he could do with the circuit, even if he doesn't like to do the exact mod twice.

 

[RR480]

PCB for v10. coming soon...rebuilt from roots

 

[Rune]

Yeah, probably the best, I mean it sounded good as it came, but with its flaws like volume drop on 2 EQ and not enough distortion and still minor noise problems and a defective on board trimpot, I started to get fustated with the thing. Since then we have new info, more techs/hobbists have participated in getting the original as good as it can get, and of course Ive learned a lot my self, could probably design my own amp with just some studying. Still trying to figure out the pot issue of the clone, will do some tests tonight.

 

[gorhrut]

redoing my gp 1000. ripped out the old pcb and replacing with turret board. same circuit, itll just be easier to modify and try different components. also working on making a full amp head with the modified gp circuit and williamson kt88 poweramp circuit(similar to vht/fryette) just need to calculate transformer values and design the layout. hopefully ill have a prototype assembled in the next couple months. could also add a built in je1000/mm04 like the gpsp had( i think) or make it as a pedal version

 

[Motorbreath_667]

I wonder if the mesa mark iic+ and the gp have similarities....
Also, I was thinking about the two masters, does it really need two? Since both of them are set exactly the same and if you would run anything between the pre amp and poweramp, most of the time you would have to use only one of the masters? It could clear some space on the front panel...

 

[gorhrut]

ill have to check the mesa stuff out.

it does not need two masters, in fact i will only be using 1 when i redo my gp. in the original gp, they werent exactly the same(100n vs 2u2 caps on the outputs) 2u2 is used to let more bass pass. the space cleared up on the front panel i am using for a pot to adjust the cathode of v2b. im going to use a 25k lin pot so you can go from really hot bias(bodom) to really cold bias(dumbles us something around 39k i think) changes tone a lot. im also bypassing that with a 1uf cap currently but i am going to experiment with 25uf(passes all guitar frequencies) and diodes/led.

once i get this preamp redone i think i will start a youtube channel with examples of changing the values of resistors/caps in amps and how to change them. there doesnt seem to be a really good channel with amp mods. uncle doug has some good amp theory stuff though.

 

[gorhrut]

mark iic has some similarities but quite a few differences too.

6 stages of common cathode gain stage vs gp's 4 stages common cathode and 2 cathode follower.
both have tonestack after 1st stage.
iic has a lot more stuff switching in and out of the circuit, also looks like it got built in reverb and eq......

 

[Rune]

A modified GP have more similarities to 2C+ specs wise, but they are both based on Fender circuits. 2C+ have a built in second EQ stage and reverb stage, which is tube driven. Also 2C+ originally dosen't have more gain/distortion than a GP-1000. Metallica had their modded the same way.

 

[Rune]

Bodom used diodes which could color the sound more than a bias pot, but it is the same deal, haven't done more research myself on my amps, beens super busy and now I spend my holidays in my family cabin, so away from everything. But I do believe that a proper ground soldering solves the internal pot trouble....

 

[gorhrut]

i think the main trouble with the gpsp internal trimpot is that it was wired wrong, if they copied that schem 100%. the schem originally shows r17(the grid leak resistor of v2a) attaching to the trim. it does not. this goes directly to ground. the internal trimpot is set up as a pre phase inverter master volume sort of thing. you can turn the trimpot up all the way to get the distortion/gain you need at lower volumes, and the master outs control the overall volume.(if that makes sense)

basically, it is set up so that all your distortion comes from the preamp. it doesnt drive the power amp hard enough to create power amp distortion(which would sound bad with kt88s anyways)




diodes and pot/bypass are different in how they effect the tone but i wont go into it unless someone REALLY cares to know.......



all of this might make no sense whatsoever as i am drunk atm.........

 

[Rune]

Yes I also think the grouding and the schem being wrong. But haven't had the time to test anything at all.... so will be right at in the following weekend. Yes I agee with all of your statement of how it works. I think my original that I tested it on had bad tubes causing feedback. And all the gpsp's have had serious trouble in the way the pot works....

 

[gorhrut]

the guys on the other forum said the grounding scheme was good but idk..... gp grounds to like 4 different places originally. that has to cause some ground loop hum.....

the one im redoing will have star grounding at first but im gonna mod this thing like crazy so ill try several different ground schemes.

one more mod is to dc raise the heater supply. probably voltage divider off the b+. this is supposed to cut down on noise a lot.



also found out that, in theory, a 12au7 works better than a 12ax7 for the cathode follower stages. v3a and b. havent tried it to see what effect it has. components should be in soon and once i have this gp redone ill try whatever mods you guys want me to.

 

[Rune]

I really don't thonk Alexi and co had all these mods on their amps. And Ive really obly experienced one noise on the gpsp and feefback issues on GP original. I wouldn't mess with any input voltage, DC or AC. The tech said that to form the sound lesser plate voltages are better, but not needed in Alexis apporach. He said something like Malmsteen had 82K (or something plate voltage(s). and the whole less is more stuff!

 

[Rune]

12au7's i've tried, less gain and also less noise of course. Not what I want...

 

[gorhrut]

ya, im sure a lot of the stuff im gonna try modding alexi did not do. i think we covered alexi mods pretty well on the other forum, so now im gonna improve(or try) on that.

did the tech say lower voltage or lower the resistor? if he said lower voltage, you would actually want to raise the plate resistors(lowers voltage into the stage).....although this would result in a larger voltage swing off the tube. so, idk, id have to see exactly how the tech wrote it.......like you said, alexi probably didnt have any plate mods. maybe he increased power supply filtering, this would make the amp have a tighter/stiffer response, again, probably not necessary though

referencing the heater supply to dc wont change the tone itll just make the amp more stable. not done in original gp's but really wouldnt hurt.

 

[Rune]

He said:
"Adding bigger anode resistor increases volume (gain), but at the same time it lowers the upper frequency knee. So it can be used in some stages, proportional to following stages reactances (specially high frequencies). Values 68k... 150k are enough usually, my opinion, with ECC83/AX7. Sometimes less is more! (Ok, I know Malmsteen statement...)"

Changing the voltage iself was not mentioned.

Another thing and a huge fun fact I discovered, you know one of the first GP-1000 previously owned by The Wings and used on their pre success demos didn't have a relay and pot. It is of course a 87 version with tube powered XLR output and thus no extra output gain. The amp was hooked up directly from distortion pot traces to C4 with only a wire. Now as we've discussed and found out it is the amps level pot. Now adding no recistance there would basically make it "on full". Now you need very silent tubes and some blocking caps to make that work OK without serious noise issues. Ive had orignal GP's tubes squeel nonstop with the pot on full. I'll finally get to test some pot wiring tomorrow on the gpsp, might get it to work one way or another. Going to ground the trimpot to input ground instead, since it is sloppy done on 88 models. If that dosen't work I'll try the pre mentioned wire solution or finally replacing the trimpot with a 1kohm LOG regular volulme pot. If none of this works well enough there has to be some other issues like the placement of R17 which bugs the shit out of me that it possibly got fucked up by that piss poor schematic found online. I actually think if I told TWCC to build it just from readings and pictures it would have been a better and more stable unit. Like we did with sp-1000, which is cloned perfectly!

 

[Rune]

R17 is definatly wrongly placed/wired after checking right now....more later, now I really wish I got involved more with the building of the gp part! It is wired to the distortion switch/pull pot insted of direct to pot, also it was wired to the ouput masters....due to piss poor schematic, feel sorry for all that used it for building clones or fixing their amp....

 

[gorhrut]

other than that 1 mistake the schematic was spot on for the wiring of my gp.

 

[Rune]

So I did some minor work on the amp today, it is so damn cold in Norway so it is hard to stay at my rehersals for more than an hour, so I tried wiring the trimpot ground to input, now that's not where it should be grounded. Because when connected there the amp squeels like hell when not playing and the pot only changes it's frequency a little bit.... Also took some pictures of studying the placement of R17... I'll get back at doing/testing the rest of this stuff tomorrow...

 

[Arystar]

I wish thsi thread became a sticky with a different name/title like "JE-1000 / GP-1000 Custom Order".

although TWCC and RR480 didnt sell as much GP replica's as they wanted, in the end they werent ready yet anyway

The JE-1000 on the other hand sold quite well I noticed and TBH its a GREAT thing that they shouldnt stop making, or they should atleast take orders for no?