Tremolux Ab763 Intensity Pot Issue

[volt9]

Hello there, quick question for all you experts I have been trying to resolve this but I am losing my patience

I build a Tremolux clone, so far everything works as should be the issue comes when I set up the vol intensity 0 and the Intensity to 10  I get a big pop and then a flat noise , turn the vol to 1 or above and disappear or turn the intensity to 9 and it disappear (no guitar connected so far)  - Tremolo pedal is not even engaged

1.- Tried 12ax and 12at tubes _nothing

2.- Isolate the issue by removing the V3 Tube only,  leaving  V2 (12AX7) , V4 (12AT), power tubes and rectifier and Nothing ("nada") same story pop and noise

3.- Changed the roach, changed the intensity pot - Nothing

4.- when removed the intensity pot lead (AKA weber shut off) - the volumen turned cero didnt pop or noise.. but this of course is because the tremolo circuitry is not longer into the equation

any ideas? thanks in advance

[HotBluePlates]

Vintage Tremolux or new build?

[volt9]

Vintage Tremolux or new build?

Clone (Blackface/Vintage)

[HotBluePlates]

I'm assuming the trem has never worked properly. I'm also assuming you used the blackface eyelet layout, given the reference to the trem roach.

Tell me more about the "flat noise". What is that? What does it sound like?

Let me make sure I understand what you've done so far:
- Noise only happens with Trem at max and (vibrato channel?) volume at minimum.
- Removing the tube used in the tremolo circuit does not change the pop or noise.
- Unsoldering a lead from the tremolo pot stops the noise.
- The trem works properly with the Intensity below maximum (you didn't say this, but you didn't say its non-functioning).

Which lead? The one going between the center lug and the optoisolator, or from the right lug (looking from the pot back, with the lugs pointing up) to the 220k resistor?

Can you link whose layout you followed? The vintage Fender layout has each of these wires descending into a hole, to be connected to the proper location under the board.

[volt9]

I'm assuming the trem has never worked properly. I'm also assuming you used the blackface eyelet layout, given the reference to the trem roach.

VIbrato Channel only (not even a tube in a normal channel)

Tell me more about the "flat noise". What is that? What does it sound like?
1.- When vol 0 and turning the Intensity pot to max (10) , a loud pop (kind of like a scratchy pot) and then static loud one kind of like a bad ground.. bbbbzzzzzzzzzzzzzzzz
2.- When Intenstiy max and turning the Vol to 0 same loud pop

Basically this issue only happens when the Vol is 0 and Intensity is 10

If any of those are differente everyting works perfect! - Tremolo works perfect, everything

Let me make sure I understand what you've done so far:
- Noise only happens with Trem at max and (vibrato channel?) volume at minimum. YES
- Removing the tube used in the tremolo circuit does not change the pop or noise. Correct
- Unsoldering a lead from the tremolo pot stops the noise. Yes removed the Lead to the 220K resistor (Signal)
- The trem works properly with the Intensity below maximum (you didn't say this, but you didn't say its non-functioning).
The intensity works perfectly when engaged Min or max doesn't matter as long as it is engaged it works flawless, the issue is when not engaged and when the pot int is at max and vol at 0

Which lead? The one going between the center lug and the optoisolator, or from the right lug (looking from the pot back, with the lugs pointing up) to the 220k resistor?   Yes removed the Lead to the 220K resistor (Signal), basically disconnect the right lug of the intensity pot

Can you link whose layout you followed? The vintage Fender layout has each of these wires descending into a hole, to be connected to the proper location under the board.
My board is a turret Board - I followed the Fender Tremolux Ab763 schematic with no alteration except that I put Orange drops 0.02,0.02,0.02 for a slower rate instead of the 0.02,0.01,0.01 - which I dont think are part of the equation

Intersting thing compared to a weber schematic is that they use a 47ohm resistor instead of the 100ohm in the PI

[sluckey]

Double check the wiring and lead dress around the intensity pot. Make sure the intensity pot and roach both have a good ground connection. Make sure there is no dc voltage on the intensity pot.

Intersting thing compared to a weber schematic is that they use a 47ohm resistor instead of the 100ohm in the PI

That resistor is part of the NFB circuit. Weber was just copying Fender. The original Fender AB763 amps used a 100Ω resistor on models that used a 2 or 4 ohm speaker load (TR, SR, Tremolux, etc), and they used a 47Ω resistor on amps that used an 8 ohm speaker (Deluxe, DR, Vibrolux, Vibroverb, etc.). Fender was just trying to keep the NFB fairly constant between different models with different speaker loads.

EDIT... Here's a Showman AB763 with a note about that resistor...

[volt9]

Double check the wiring and lead dress around the intensity pot. Make sure the intensity pot and roach both have a good ground connection. Make sure there is no dc voltage on the intensity pot.
Assuming there is an existing DC on the intensity pot, which caps should be suspects ? Any idea? AB763 ciruit

Intersting thing compared to a weber schematic is that they use a 47ohm resistor instead of the 100ohm in the PI

That resistor is part of the NFB circuit. Weber was just copying Fender. The original Fender AB763 amps used a 100Ω resistor on models that used a 2 or 4 ohm speaker load (TR, SR, Tremolux, etc), and they used a 47Ω resistor on amps that used an 8 ohm speaker (Deluxe, DR, Vibrolux, Vibroverb, etc.). Fender was just trying to keep the NFB fairly constant between different models with different speaker loads.

EDIT... Here's a Showman AB763 with a note about that resistor...

[HotBluePlates]

Assuming there is an existing DC on the intensity pot, which caps should be suspects ? Any idea? AB763 ciruit

Probably the 0.1uF cap from V2 pin 6. Or a strange issue with the trem roach.

But since this is a new amp, you're very unlikely to have bad parts, but rather a wiring or lead dress issue.

[volt9]

Assuming there is an existing DC on the intensity pot, which caps should be suspects ? Any idea? AB763 ciruit

Probably the 0.1uF cap from V2 pin 6. Or a strange issue with the trem roach.
Replaced the Roach already with no luck, I will make some readings and log results
Thanks in advance

But since this is a new amp, you're very unlikely to have bad parts, but rather a wiring or lead dress issue.

[volt9]

Assuming there is an existing DC on the intensity pot, which caps should be suspects ? Any idea? AB763 ciruit

Probably the 0.1uF cap from V2 pin 6. Or a strange issue with the trem roach.
Replaced the Roach already with no luck, I will make some readings and log results
Thanks in advance

But since this is a new amp, you're very unlikely to have bad parts, but rather a wiring or lead dress issue.

Found the issue - lead dress from the Bias .. Thanks!