high gain lee jackson gp 1000

[Gorhrut]

r15 is the 100k plate resistor for v1a. probably best not to remove that....

you should try wiring it how i showed in the pic with the push/pull removed.
in the other pics there are still a lot of pre distortion and post distortion traces right next to each other.


of course, its also possible i just misunderstood what the tech meant....???

also, if you get a chance can you post some pics?

[Rune]

r15 is the 100k plate resistor for v1a. probably best not to remove that....

you should try wiring it how i showed in the pic with the push/pull removed.
in the other pics there are still a lot of pre distortion and post distortion traces right next to each other.


of course, its also possible i just misunderstood what the tech meant....???

Yeah, sorry I ment the wire/resistor parallel with the relal. Did not remove R15.... Yeah, will try it out but not today.

Cameron; The GPSP thread? And what will it show me?
Havent heard any Dumble doing metal.

[Cameron]

Okay, so removed the relay, D5, R15 (which essentially is a wire). Did no cutting at all. And rewired from points in pic 3 and 4 in Gorhruts post . Got audio and it sounds just the same. With noise and all. Maybe if I wired it from the internal pot I'd get better results. The layout of the clone is a tad better and easier to work with even if its smaller. And maybe if I cut some traces it would get better....

What thread on the Bodom forum? And what would it show me?

Lee Jackson GP-1000 got more natural distortion than the Dumble amps I've heard. Or???

I'm wondering what noise you are hearing? is it with the guitar off ? does it have a pitch? or is it a hissing ...you know. Do you have a recording of the noise? I'm just trying to get a better idea as to what you are hearing.

[Cameron]

r15 is the 100k plate resistor for v1a. probably best not to remove that....

you should try wiring it how i showed in the pic with the push/pull removed.
in the other pics there are still a lot of pre distortion and post distortion traces right next to each other.


of course, its also possible i just misunderstood what the tech meant....???

Yeah, sorry I ment the wire/resistor parallel with the relal. Did not remove R15.... Yeah, will try it out but not today.

Cameron; The GPSP thread? And what will it show me?
Havent heard any Dumble doing metal.

I know ....its too bad ...Dumbles are great amps and can do very heavy tones but most guys are doing the RF type stuff. Go look and compare the schematic... you could use the same layout. You could mod the Dumble to a Jackson easily or the Jackson into the Dumble. Its like the Jackson is a simplified version of a Dumble. You guys on that forum even put in the other tone stack ...like the Dumble has.

And..It shows me ... don't over think things...this was never a unique preamp ...too much mojo and mystery put on this preamp there.......also never copy a layout...you will usually copy its mistakes also......and its not cool and thats where you can get into trouble and have Lee's lawyers send you letters ...this is a very simple preamp ..that tech should have known this stuff.......you should also know more then d7 r3 and thats stuff.......know what the parts are because those numbers are going to change if another schematic is made...the programs generate these numbers...and are more for the assembler that does not care what part value ...its just bins and those numbers...but a tech needs to know what part and where it is in the circuit and is function in the circuit. That will help you see the parts that are the problem ...........its like you need to know where the water flows before you cut the pipe.....if the plummer does not know where the water flows ..he should not be cutting any pipe! and don't want him working on my house I'm only saying this to help you .....not to be a dick Just slow down ...soke some of this in ... I am telling you this from learning from my own experience...so I do understand
Its too bad you are not near me ...I would say come by and we'd have that up and the way you want it in about 2 hours....If you ever come to the US and Los Angeles ...bring it with you

There is one thing you said ...The trim(gain Ch output) pot on some of these was 50k ...I just found my old notes from the late 80's It seems one I had ...had a 1.5k in the last cathode instead of 10k ...and either a .22 or .022 (schematic is messed up here...its old)over the 5.6k cathode resistor......stock from the factory.

I think Gorhrut is getting it together.

[Gorhrut]

I think Gorhrut is getting it together.

thank you. learned a ton since i started this thread. a lot of the mods ive done were suggested on page 1 but i didnt understand them at the time. now im getting value from this whole thread and still finding more in it every day.[/quote]

[Cameron]

For the relay ...another idea ..would be to move the plate resistors and coupling caps to the tube sockets ...then run shielded cable to the relay but mount it up side down on the circuit board ...bypass the traces and run the shielded wire directly to the relay...also pullout the distortion pot from the board reinstall it with the tabs up and wire directly to it bypassing the traces on the board....for the traces that now connect to nothing ....wire these to ground. Also now that I see these notes...I think the cap ...C3 should be .1 not 1mf...over the 5.6k resistor.

[Cameron]

Another thing ....Lee originally designed this with one gain stage added for the distortion ...the 87....this circuit puts the signal coming back into the board out of phase ..this will suppress these problems.....when he added the second... extra gain stage...88....the phase... is now in phase coming back to the board .....its a bit like positive feedback or is...so you will get funny stuff in the hi-end and oscillation...if you add gain without fixing this...it will only get worse......

[Gorhrut]

for the traces that now connect to nothing ....wire these to ground.

what advantage does grounding these have?


and im not gonna pretend for a second that i understand what you said about phase and positive feedback....

what effect do these have? where in the circuit do they occur? and what are some possible solutions?

[Cameron]

for the traces that now connect to nothing ....wire these to ground.

what advantage does grounding these have?


and im not gonna pretend for a second that i understand what you said about phase and positive feedback....

what effect do these have? where in the circuit do they occur? and what are some possible solutions?

1...It helps shield things a bit better

2...Its what/where the problem is ....the output of the last stage coming back into the board next to the distortion pot and traces ....being in phase with each other. I think ....if you just put the last cap and plate resistor on the socket and ran a shielded wire directly to the master output volume where the shielded wire goes that comes from near the relay and jumps over to the masters....take that out .....put your wire there instead.....I think will bypass the problem. You can do this without cutting the traces...its best not to cut the traces...not ..at least until you know how to fix it.....

Also the 10k in the cathode of the last stage is giving off allot of signal ...so if it still has a problem ...I might wire this directly to the socket too..

[Gorhrut]

Its what/where the problem is ....the output of the last stage coming back into the board next to the distortion pot and traces ....being in phase with each other. I think ....if you just put the last cap and plate resistor on the socket and ran a shielded wire directly to the master output volume where the shielded wire goes that comes from near the relay and jumps over to the masters....take that out .....put your wire there instead.....I think will bypass the problem. You can do this without cutting the traces...its best not to cut the traces...not ..at least until you know how to fix it.....

instead of the internal trimpot, i have a pot on the back of the preamp. i could wire this directly to the master out instead of routing back onto the pcb (in effect removing the cable by the relay) would this accomplish what youre suggesting?


i can try and make a pic really quick...

[Gorhrut]

[img:690:920]http://i.imgur.com/drobvYV.jpg[/img]
top view of pcb.
wiper of trimpot goes to master outs


[img2073]http://i.imgur.com/lVMKcyn.jpg[/img]
bottom view of pcb
from coupling cap of v1b to distortion pot



my gp makes wiring it this way pretty easy

[Cameron]

Its what/where the problem is ....the output of the last stage coming back into the board next to the distortion pot and traces ....being in phase with each other. I think ....if you just put the last cap and plate resistor on the socket and ran a shielded wire directly to the master output volume where the shielded wire goes that comes from near the relay and jumps over to the masters....take that out .....put your wire there instead.....I think will bypass the problem. You can do this without cutting the traces...its best not to cut the traces...not ..at least until you know how to fix it.....

instead of the internal trimpot, i have a pot on the back of the preamp. i could wire this directly to the master out instead of routing back onto the pcb (in effect removing the cable by the relay) would this accomplish what youre suggesting?


i can try and make a pic really quick...

No....you still have the in phase signal on the board ..plate resistor and coupling cap need to go to the tube socket.

[Gorhrut]

ok, i think i understand.

[Gorhrut]

finished modding. removed relay and all components that went along with that. moved v1b coupling cap onto the pin and ran wire straight to the distortion pot. had to leave the plate resistor because both v1a and b plates connect to b+ on the board. ran wire from p100(pot on back of preamp for mine) to the master outs. somehow managed 0 lifted traces/pads first time modding pcb. overall sounds really good.

i ran a test before modding. removed guitar cable from amp, all tone controls max and onboard trim maxed. there was high pitch squealing like crazy. adjusting the volume and distortion changed the pitch of the squeal but volume stayed the same. wish i had recorded it, it was pretty crazy... also got radio station when i touched the volume pot...

now that mods are done i tried the same test and squealing is gone. tried everything to recreate the squeal but couldnt do it. (guess thats a good sign) and no radio stations. only thing is a moderately loud hum that was there before. i didnt use shielded cable cuz i didnt have any on hand but ill switch it out when i do and see if that helps.

will post pictures tomorrow, and sound clip when i get my new poweramp...

[Cameron]

finished modding. removed relay and all components that went along with that. moved v1b coupling cap onto the pin and ran wire straight to the distortion pot. had to leave the plate resistor because both v1a and b plates connect to b+ on the board. ran wire from p100(pot on back of preamp for mine) to the master outs. somehow managed 0 lifted traces/pads first time modding pcb. overall sounds really good.

i ran a test before modding. removed guitar cable from amp, all tone controls max and onboard trim maxed. there was high pitch squealing like crazy. adjusting the volume and distortion changed the pitch of the squeal but volume stayed the same. wish i had recorded it, it was pretty crazy... also got radio station when i touched the volume pot...

now that mods are done i tried the same test and squealing is gone. tried everything to recreate the squeal but couldnt do it. (guess thats a good sign) and no radio stations. only thing is a moderately loud hum that was there before. i didnt use shielded cable cuz i didnt have any on hand but ill switch it out when i do and see if that helps.

will post pictures tomorrow, and sound clip when i get my new poweramp...

You can see how getting that off the circuit board helps.
After I ate tonight ..I thought I would put this circuit in an old Deluxe amp I made...

I just used parts I had on the bench..It works great...looks like shit..just did it in an hour.... ..but its just so I can remember and refresh my memory. I added way more gain ..first two cathodes are 1k/1mf and the distortion stage is 5.6k/1mf and on the last stage I put 820 ohm instead of the 10k.......I also added a 330pf over the 220k going to ground at the grid of the last stage to keep the hi end down a little and I also just liked it better with it. I'll try to put up a crappy cellphone clip. I'm kind of having fun playing this.... brings back memories of 1989