Marshall Origin noise

[Valvehead]

Ive got a Marshall Origin 20 here with a nasty buzz/hum. Ive been chasing it for a long time and now I finally have a scope . I modded the amp according to Headfirst amps and its basically converted to a jcm 800 preamp. The amp sounds very good but....the buzz.
So , id like to give you all the info and Ill post scems and pics / video .

'The buzz can be killed with the master volume so i assume its before that .
Ive swapped tubes , and pulled the pcb out a couple times to inspect. ALL grounds check good with meter as do ALL shields on the cables . All pots are grounded as is the main Pcb .
I know its something with the mods. Ive also clipped a wire to ground and touched all ground points in the preamp

Ive went back and watched the mod video several times and everything looks good.

Here is what Im seeing on the scope ( will post a pic of V2/ Pin 2 )

Input jack and all of V1 sine wave is smooth and flat

V2
pin 1 noise on scope
p2 Noise (this is where its loudest on scope )
p3 noise (this goes to tone stack )
p6 noise (tied to pin 2 )
p7 NO noise
p8 No noise

so here is the stock scem , the hand drawn new layout , a video of the buzz

you will see the stock preamp is kinda funky as far as a Marshall

Im new to O scopes so maybe you guys can help me pinpoint the issue

https://youtu.be/bBq2114QDtc



Origin_20_Main_PCB.pdf

[The Dude]

FYI: Video is marked private so we can't see it. Can you fix it and make it public?

[Valvehead]

Ok-- should be fixed.

https://www.youtube.com/watch?v=bBq2114QDtc

forgot to mention..the modded version uses V2 pin 3 as the cath follower .

[Jon Snell]

What happens if you lift the 22n capacitor ... if the noise stops it is from V1.

[Helmholtz]

Can you change your scope setting to 10 ms/div (second button from left)?

[Valvehead]

What happens if you lift the 22n capacitor ... if the noise stops it is from V1.

no change at all

[Valvehead]

Can you change your scope setting to 10 ms/div (second button from left)?

Yes 10ms

here is V2 pin 2

[Pedro Vecino]

Can you put the schematic of the other part of the circuit? Tilt, eq, master volume...
Very thankful.

[Helmholtz]

Yes 10ms

here is V2 pin 2

Scope resolution is rather poor.
Fundamental frequency looks like 60Hz.
Maybe try 2ms/div.

[Valvehead]

Can you put the schematic of the other part of the circuit? Tilt, eq, master volume...
Very thankful.

I dont have have that . The mv , tilt , eq are all on a seperate pcb. The mod doesnt touch that pcb...all stock . All solder joints were checked on that board

[Jon Snell]

no change at all

What happens when you apply a ground to pin 2?
If still noisy, replace the anode load resistor/valve.
To have more noise on the grid (oin 2) than the anode (pin 1) makes no sense.
(Count from the underside of the valve base in a clockwise direction.)

[Helmholtz]

Can you add tube pin numbers in your drawing?

Have you tried a different ECC83 in V2 position? Some develop excessive heater hum.

Also please post a link to the mod video.

And post a scope pic of the noise with 2ms/div.

[Helmholtz]

What happens when you apply a ground to pin 2?
If still noisy, replace the anode load resistor/valve.
To have more noise on the grid (oin 2) than the anode (pin 1) makes no sense.
(Count from the underside of the valve base in a clockwise direction.)

I think his V2 wiring is grid pin 7 = input of gain stage, plate pin 6 connected grid pin 2 of second triode (CF).
So grounding pin 2 also grounds the plate of the first triode.
I think you meant grounding the input grid (pin 7).

Noise level should be the same on V2 pins 2, 6 and 3.

[Jon Snell]

I think his V2 wiring is grid pin 7 = input of gain stage, plate pin 6 connected grid pin 2 of second triode (CF).
So grounding pin 2 also grounds the plate of the first triode.
I think you meant grounding the input grid (pin 7).

Noise level should be the same on V2 pins 2, 6 and 3.

If it is V2b then yes, pin 7 is the grid.
Removing that 22n coupling capacitor stops any noise from the previous valve stage and if there is more noise on pin 2, that means the grid of V2a is noisy, which is V2b anode pin 6 therefore either the Anode load resistor is noisy or there is noise on pin 7 of V2b.
If the coupling capacitor (22n) is removed, the only path for noise is something on the grid, pin 7 or the valve is noisy.
The diagramme very simple, there are only a possibility of four components involved and of course bad soldering.

[Helmholtz]

Sure, I just think that with this wiring grounding of input grid pin 7 is more interesting than grounding the plate.

Also a noisy plate resistor will hardly cause a hum as heard in the vid of post #1.