high gain lee jackson gp 1000

martin manning · Post by **martin manning** » Thu Dec 18, 2014 12:30 am

I don't think moving that resistor to the socket pin is doing anything for hum frequencies. I suspect there was a bad solder joint or something that you unknowingly corrected in the process.

Gorhrut · Post by **Gorhrut** » Fri Dec 19, 2014 7:39 am

just got my prototyping boards to make the amp head.

heater wires and ground wires all hooked up in 15 minutes for the preamp portion of the amp. ordered components from mouser today so ill post more pictures as i get them hooked up.

[img

2340]http://i.imgur.com/vW6Xd4V.jpg[/img]

Gorhrut · Post by **Gorhrut** » Sat Dec 20, 2014 9:13 am

messing around with my gp 1000 again trying to pin down this hum issue.

randomly decided to check filter caps. on the schematic, these are 47uf caps. all 3 of mine were at 90+ uf. could this be a sign of caps going bad? is this a significant source of hum?

martin manning · Post by **martin manning** » Sat Dec 20, 2014 1:43 pm

Usually the capacitance will measure low, and the ESR high in failing caps. If they are over spec, that should reduce the power supply ripple.

Gorhrut · Post by **Gorhrut** » Wed Dec 24, 2014 3:09 am

im removing the pcb in this and rebuilding on turret board. all components and hardware should be here by the 30th. but i have a few questions...

would there be a big change in tone by removing the split loads on both halves of v2 and just replacing with 100k each?

im just going to use 1 half of v3. for heaters, do i still run wires the same(pin 4+5 together and pin 9) or is there some other way since im just using 1 half right now?

would there be any advantage to using a choke instead of the resistors in the power section? change in tone? ive heard this might reduce noise, possibly enhance low end response. how would i set this up?(just replace 1 resistor? replace both with 2 chokes? if 1 resistor, which one?)

thanks to all for helping me with the mods and thanks for teaching me a lot along the way.

if it turns out good i will definitely upload pics and updated schems and such.....

here is the layout
[img:5396:2400]http://i.imgur.com/aJqGYKO.png[/img]

i am planning to have a ground wire going all along the outside of the board(shown in black on layout) so that i can easily solder on shielded cable wherever i need to. this shouldnt cause any issues, right?

Smokebreak · Post by **Smokebreak** » Wed Dec 24, 2014 6:12 am

If you abandon the split plate loads, you will get way more gain, but not the kind you're looking for. You can look at it as a voltage divider, as AC signal sees B+ as ground. So a 47K/47k split cuts the signal down considerably. With just a 100k , the amp may oscillate, or maybe sound like doodoo. You can certainly experiment with this section though. I think I had 22K/82K in mine, but had the amp running hotter in other places.
The 10K/100k wouldnt be as drastic a difference if you just replaced it with 110K, but at that point, I'd think you'd also be altering the frequency reponse, to an extent.

Gorhrut · Post by **Gorhrut** » Wed Dec 24, 2014 7:03 am

good to know. once i get the amp up and running i will try both and maybe make a vid for anyone interested in the differences....

i might start a youtube channel answering my own beginner questions with examples.

also, just realized the two 47k are not actually "split plate". its two in series and 1 has a plate bypass cap. reduces gain around 1khz. so removing this passes high mids slightly more.

Smokebreak · Post by **Smokebreak** » Wed Dec 24, 2014 7:27 am

Ha! You're right. I was thinking of the Rivera stuff, which does have the split on the 3rd stage

Gorhrut · Post by **Gorhrut** » Wed Dec 24, 2014 7:36 am

Smokebreak wrote:Ha! You're right. I was thinking of the Rivera stuff, which does have the split on the 3rd stage

its cool. ive been looking at this same schematic for months and just now realized it. lol.

Cameron · Post by **Cameron** » Wed Dec 24, 2014 8:51 am

Gorhrut wrote:im removing the pcb in this and rebuilding on turret board. all components and hardware should be here by the 30th. but i have a few questions...

would there be a big change in tone by removing the split loads on both halves of v2 and just replacing with 100k each?

im just going to use 1 half of v3. for heaters, do i still run wires the same(pin 4+5 together and pin 9) or is there some other way since im just using 1 half right now?

would there be any advantage to using a choke instead of the resistors in the power section? change in tone? ive heard this might reduce noise, possibly enhance low end response. how would i set this up?(just replace 1 resistor? replace both with 2 chokes? if 1 resistor, which one?)

thanks to all for helping me with the mods and thanks for teaching me a lot along the way.

if it turns out good i will definitely upload pics and updated schems and such.....

here is the layout
[img:5396:2400]http://i.imgur.com/aJqGYKO.png[/img]

i am planning to have a ground wire going all along the outside of the board(shown in black on layout) so that i can easily solder on shielded cable wherever i need to. this shouldnt cause any issues, right?

Go check out Dumble layouts...They have been built and are proven to work ...plus you can see how to keep the switching ....or not...but there are some good layouts in that section you can start with. The circuits ideas are very similar...and most of the info can/will apply to the LJ preamp/amp also.

Gorhrut · Post by **Gorhrut** » Wed Dec 24, 2014 8:54 am

will do, cameron.

any specific layout from the dumble files or just check them all out?

Cameron · Post by **Cameron** » Wed Dec 24, 2014 2:35 pm

Gorhrut wrote:will do, cameron.

any specific layout from the dumble files or just check them all out?

All the info....these are basically modded Fenders ..adding 2 gain stages after the Fender clean and both switch the circuit in and out in a similar way. This is Lee's ..or Paul's

..version of a Dumble type circuit. You will see a lot of mods and tricks that will apply to the LJ preamp as well ways to keep the noise down.
You will also see a version with an extra tone stack for the gain channel only..its a simple board with trim pots...very easy ... its after the last gain stage ...I think for the tone you are trying to get .....you should try that...you can also switch it in/out....don't be afraid to try different types of tone stacks here. Back in the mid 90's I built one with an active type tone stack for a guy that owned a studio ...... It was extremely good at covering hundreds of different tones and styles....from pretty cleans to very heavy 7 string type stuff by playing with the two sets of controls...very versatile and fun to play.

Cameron · Post by **Cameron** » Wed Dec 24, 2014 3:39 pm

Gorhrut wrote:
im just going to use 1 half of v3. for heaters, do i still run wires the same(pin 4+5 together and pin 9) or is there some other way since im just using 1 half right now?

would there be any advantage to using a choke instead of the resistors in the power section? change in tone? ive heard this might reduce noise, possibly enhance low end response. how would i set this up?(just replace 1 resistor? replace both with 2 chokes? if 1 resistor, which one?)

thanks to all for helping me with the mods and thanks for teaching me a lot along the way.

if it turns out good i will definitely upload pics and updated schems and such.....

i am planning to have a ground wire going all along the outside of the board(shown in black on layout) so that i can easily solder on shielded cable wherever i need to. this shouldnt cause any issues, right?

Don't do the cathode follower ..unless you are going to put in a loop ....the output of the preamp.... would be the send of the effects loop in the amp version..If no loop...... just go from the master... to the input of the phase-inverter. You will see what I'm saying as you look at the Dumble stuff.

Also ....build it like you see it ..same power supply and filtering ...then mod it ...don't get to far ahead of you're self...
Pick one of the D layouts for how to do you're grounds. You have a ground loop the way you have it drawn. If you are not sure about ground loops and things like this ...then use a D layout after reading some of that stuff........READ/ Learn ...It will make the whole picture much clearer for you.

Gorhrut · Post by **Gorhrut** » Sun Dec 28, 2014 6:33 am

would removing that cathode follower stage have any tonal disadvantages?

from reading it seams it just deals with impedence. and there would be no change in phase since signal came off the cathode, right?

also, this is causing me some confusion:
[img

1012]http://i.imgur.com/roFwjir.jpg[/img]

does this mean that the heaters have a full wave rectifier and 2200uf filter cap? or are these ac heaters and the diodes/cap just for the led and relay? still learning how to read the power section of schems.....

im thinking they are ac heaters. which could benefit from dc elevation?
lol, im sure every question i ask shows just how much of a noob i am......at least i know to discharge filter caps

roberto · Post by **roberto** » Sun Dec 28, 2014 10:32 am

The CF has also a tonal impact on the sound, and you are right about the AC heaters, and DC just for led and relay.

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