high gain lee jackson gp 1000

[Rune]

Gorhrut: On the GPSP clone project, my tech got understood the email wrong, you see an old Finnish tech writes poor english and you could misunderstand him. The purpose of the pot was/is to find a tone you like easier than swapping the resistor until you get the right tone. Also make up for the lost volume drop made by diodes. The cap was also suggested, but you could do without as well and have diodes there.

The noise is still there with minimal modding. Just try slamming a TS with a lot of drive in front and see what happens to the decays of notes/chords. I can post a recording of it tomorrow or something, it is like a buzzy gnarly sound that comes present when notes ring out, most prominent on low E but other strings, chords as well. Palm muting is a mess with it and it is on the clean channel to, and if you lower distortion and gain. low treble somehow tames it, but then the tone suck.

I actually have made new boards, but with the same issue (because I didn't have the info on what was causing it). I have a clone of the unit and used to own a second original. And I have swapped and added parts and wires before. So only new thing would be cutting the board, which needs to be done anyways. Could buy a new unit if everything fails. it is quite cheap nowadays when Alexi and co dropped it for high gain Engls and Marshalls. I've seen units go for $200.....

No nobody goes around handing schematics of mods they make money of, that would be stupid, so no didn't get that from the tech, just values and vague info.

The distortion push pull system seems glued to the pot. but the backside picture should determin it. Clone has a modern mini switch system, that I wanted instead of push/pull. Could be easier to get the info from it. Same design and layout.

[Cameron]

Ive had 4 of these. I've been playing my LJ Blues59 alot lately. I'm very familiar with Lee's stuff...Ive never had this problem...only one early preamp I had a long time ago did this...and that I fixed by doing what I posted.... If you built a new board ...with a better layout??(don't do the same layout)..and still got the same problem??...I don't know what to tell you....its a simple preamp with not even allot gain to have problems with?? ...Ive built a few of these with more gain for friends and never had a problem...very easy. To me...I get the feeling...you are a guy trying to make a product to sell ...and you've gotten in over you're head with the project..... not a bad thing ..you just need to be more up front with what you are trying to work with....or more clear ...if you want help.

[Rune]

Lee Jacksons made many good amps, but they all got a lot of criticism nowadays. A lot of people says they´re to fizzy/noisy. But I find them perfect for what they do.

I have made new PCBs, but that was before I knew what caused the issue and how to fix it, so they got mostly the same design (with errors and all).
Also before I knew about all the mods possibilities too. Made the clone with two techs/electricians from Slovakia, where one of them is excellent at what he dose, but don't have that much experience with audio amplifiers, but he's getting there.

I for myself know how to solder, rewire, change parts, but I'm not educated enough on building amps, I understand a lot of it, but not all the technical aspect. But I know a lot of stuff in this design and self teaching me about the areas where the modifications could be placed and what it really dose, technically speaking as well.

And the guy providing me with info is a quite famous tech in Finland, who is famous for working on Dumble, Lee Jackson and Marshall circuits making them more modern. He's been doing modifications since I was i diapers so kind of trust that he knows what to do.
Also talked with Larry (Larrys Amplification) from Germany who did some mods on the unit 10-20 years ago and he had some input on other things that could be done in the tone stack.

I'll test out that grounding idea of yours first as it seems like it is easy, especially since I personal don't own and oscilloscope for tracking the issue and repairing traces is a lot harder, and I know that cutting the clean and relay out of the system can be avoided.

Although the techs from Slovakia I worked with making a clone did test it with an oscilloscope and found some issues, but where never able to fix them properly. One thing they tried was adding a small cap to R202 trying to block some of the harsh frequencies, but I felt that it took too much out of the overall treble in the amp, kind of dulled the harmonics somewhat.

I personally aren't/weren't making any money of the cloning project, and I'm really not looking to sell anything, I just wanted to see if it was possible to make this amp stable when pushing it with more drive.

That is as clear as I can get. Now with all these pictures and mod suggestions and possibilities to get measurements and more info/pictures I thought maybe someone here knew about similar designs and how to fix these kind of issues. Like the Fender Concert II and Metaltronix M-1000 is very similar in design to this and are far more common amps.
You said Dumble has similarities, but I have yet to be impressed by those amps when it comes to heavy music. Kitty Hawk Preamp(s) on the other hand is awesome.

[Cameron]

Lee Jacksons made many good amps, but they all got a lot of criticism nowadays. A lot of people says they´re to fizzy/noisy. But I find them perfect for what they do.

I have made new PCBs, but that was before I knew what caused the issue and how to fix it, so they got mostly the same design (with errors and all).
Also before I knew about all the mods possibilities too. Made the clone with two techs/electricians from Slovakia, where one of them is excellent at what he dose, but don't have that much experience with audio amplifiers, but he's getting there.

I for myself know how to solder, rewire, change parts, but I'm not educated enough on building amps, I understand a lot of it, but not all the technical aspect. But I know a lot of stuff in this design and self teaching me about the areas where the modifications could be placed and what it really dose, technically speaking as well.

And the guy providing me with info is a quite famous tech in Finland, who is famous for working on Dumble, Lee Jackson and Marshall circuits making them more modern. He's been doing modifications since I was i diapers so kind of trust that he knows what to do.
Also talked with Larry (Larrys Amplification) from Germany who did some mods on the unit 10-20 years ago and he had some input on other things that could be done in the tone stack.

I'll test out that grounding idea of yours first as it seems like it is easy, especially since I personal don't own and oscilloscope for tracking the issue and repairing traces is a lot harder, and I know that cutting the clean and relay out of the system can be avoided.

Although the techs from Slovakia I worked with making a clone did test it with an oscilloscope and found some issues, but where never able to fix them properly. One thing they tried was adding a small cap to R202 trying to block some of the harsh frequencies, but I felt that it took too much out of the overall treble in the amp, kind of dulled the harmonics somewhat.

I personally aren't/weren't making any money of the cloning project, and I'm really not looking to sell anything, I just wanted to see if it was possible to make this amp stable when pushing it with more drive.

That is as clear as I can get. Now with all these pictures and mod suggestions and possibilities to get measurements and more info/pictures I thought maybe someone here knew about similar designs and how to fix these kind of issues. Like the Fender Concert II and Metaltronix M-1000 is very similar in design to this and are far more common amps.
You said Dumble has similarities, but I have yet to be impressed by those amps when it comes to heavy music. Kitty Hawk Preamp(s) on the other hand is awesome.

Just build the preamp yourself ...its simple...you need to learn more about this stuff anyway. You have read stuff...but from the things you said in this thread ...you have ...without experience..... got some things a bit off on how this stuff really works.....and thats what what people where questioning earlier in this thread. You could use some of the Dumble preamp layouts to start you off. Go read the thread on the Concert amp ...that circuit is the fender circuit Lee talks about that was the first preamp....from that ...and with the info you have...you can add the extra gain stage and see how to add an independent clean also.

The M-1000 is nothing like the preamp. The preamp is in the Dumble/Fender type circuit(tone after 1 stage).... The M-1000 and the rest of the amps he designed are the Marshall type circuit(tone after the last stage...and others with a gain stage after this). Lee only used this Fender type circuit(even tho he says the 2nd run is marshall like ...its not..its the tone he was tying to get)...... in the preamps...not in the amps.....maybe because.... The guy that designed this circuit is not Lee....its Paul Rivera. I worked on a few Fender's that Paul did this mod on...mid boost and every thing......earliest one was a Fender Princeton ...done in 1974. Also I used to go to Harmony Music when I was a kid ...I lived down the street ....before Lee made it his shop. It was one of my favorite stores ever ......I learned allot asking those guys and Lee A billion questions .... The first ever soldering iron I had ..it was in box of cables that I was looking through at that store.

[Gorhrut]

[img2178]http://i.imgur.com/H1UykYa.jpg[/img]

im going to try making a version of this amp without pcb and without all the push/pull nonsense and no clean, only distortion.

does this look right? i just removed all the push/pull stuff in the schematic. i also removed the midshift and left the value that i like the tone at.[/img]

[Cameron]

[img2178]http://i.imgur.com/H1UykYa.jpg[/img]

im going to try making a version of this amp without pcb and without all the push/pull nonsense and no clean, only distortion.

does this look right? i just removed all the push/pull stuff in the schematic. i also removed the midshift and left the value that i like the tone at.[/img]

Leave the mid boost stuff in its very useful..... go from the out of the fender clean..into the overdrive ...master is p100. There is another mistake ...if you don't see it ...go read some more about how this stuff works.. before you start.

[Rune]

No, P100 is certainly not the Master, and I believe it is an error in the schematic. P100 is the pot in the middle of the PCB, it sets the volume between clean and distorted signal. On my clone it is kind of fucked up, believe it got built wrong. On my original it works until at highest settings, then there is HF oscillating and tube feedback all the way, nothing but it.
Value of P100 is 10k, not 1M. I believe the relation between this pot and the relay is the real issue.....but I'm no pro. What happens if ypu were to remove it and R17 from the circuit.

[Gorhrut]

@cameron

is this more accurate?
[img2176]http://i.imgur.com/pDxqAOx.jpg[/img]



@rune, on my gp, i havent had any oscillation that i can tell when p100 is turned all the way up. what brand of 12ax7 are you using? ill also have to check what value my p100 is because i thought i checked all my component values against this schematic and they looked correct. mine is weird though because i have an actual pot in the back of my gp instead of the trimpot built on the pcb. ill check the value today and edit this post with it later.

[billyz]

C9 connects to P2 (pot). P100 connects to p6,and p7. Loose the connection between p2 and p100.
I am a bit perplexed by r17, is this right or some kind of feedback loop? I would think it forms the voltage divider and should be grounded.
Good luck, you've come a long way to understanding these circuits.

Billy Z

[Rune]

Actually R17 is connected to the distortion pot and not P100 and it is wired to the masters. P100 is connected to ground/C4/C9. Nothing else.

And you havent removed the relay completly.

It has been a while since Ive tried it on full with an original, but my 87 (which I sold) made feedback noises on full, unmodded. It had 3 Groove tube 12AX7C.

Ive heard about those units with the pot on the back, those are quite rare. Can you take a photo of the main PCB and post it here?

[Gorhrut]

@rune



@billy, hey, nice to see you on here. ive come a long way since i first came into your shop but i still got a LONG way to go!!

[Rune]

I don't use that schematic, it is like a swizz cheese of errors.

[billyz]

Actually R17 is connected to the distortion pot and not P100 and it is wired to the masters. P100 is connected to ground/C4/C9. Nothing else.

And you havent removed the relay completly.

It has been a while since Ive tried it on full with an original, but my 87 (which I sold) made feedback noises on full, unmodded. It had 3 Groove tube 12AX7C.

Ive heard about those units with the pot on the back, those are quite rare. Can you take a photo of the main PCB and post it here?

Ok, looking at the original schematic. I see c9 connects to p2. P100 is grounded to form a divider. The middle leg of p100 connects to master (p6,p7). R17, seems to serve a multifunction function of grid load and feedback.

I have been inside gorhuts gp1000, but don't remember , is p100 an internal trimmer?
You nutty guys and your ultra high gain stuff!

[billyz]

I don't use that schematic, it is like a swizz cheese of errors.

It's been a while since I worked on gorhuts preamp. But I do not recall errors in this schematic . Perhaps there are different gp circuits , but his follows this schematic, or did until the mods.
Gorhut is pretty sharp and wants to learn . He did bite off a big one with experimenting on this pre, especially since it is on a pcb. I do think it would be better to build one with turrets and wires to experiment on.

Good luck,
Z

[Gorhrut]

@billy, on most gp1000s it is an internal trimmer, but on mine it is a minipot on the back of the chassis

@rune, do you have a better schematic to work from? i would greatly appreciate an upload....or maybe not if billy says mine is good...