Tone stack issues (Fender 75 amp)

[Dreadneck]

As suggested from another thread concerning this amp, I start a new thread regarding issues with the tone stack.

It doesn't work at all. Turning the pots does nothing. The bright switch also has no effect.

It is the Fender 75 amp so the tone pots has a push-pull function for boost. Those work except for the middle boost that only seems to lower the amps volume........

But the first problem is fixing the wiring of the tone pots. I attach the schematics and also a drawing I made of how it looks now.
I have major trouble working out the wiring from the schematic..

Any help would be greatly appreciated!

 

[Jon Snell]

If there is a bad ground connection, the tone controls and boost control will not do anything.
Check the ground point.

 

[Dreadneck]

The grounding you point out is there and in good shape. I'll look for other possible ground errors.

The way the wiper arrow is pointing in the schematic on the bass and mid pots, does that mean it is tied to lug 1?
If it was tied to lug 3, would the arrow be angled differently?

 

[YellowBoots]

Here’s my best attempt at wiring it according to the schematic. Check for errors because it is easy to make them.

1. Verify the mid boost switch also has a 100K/.0047u shunt to ground like I have drawn. Mid boost is wired to left lug of mid pot—not wiper of mid pot.
2. The 250p to right lug of treble pot comes before the 100K.
3. Treble wiper is wired to right lug of volume pot.
4. Bright switch is wired to wiper of volume pot—not wiper of treble pot.
4. 120p bright cap runs from treble wiper to bright switch—not right lug of volume pot.
5. I don’t see an 820K in parallel with the bright cap on the schematic. Should work with or without.

Give that a spin and see if there’s any improvement. I bet there are other ways to lay out the wiring for the tone stack—I’ve only illustrated one option. If the pot lugs get too many wires, you may have to look elsewhere to make connections while maintaining the integrity of the circuit. Good luck, hope this helps.

 

[Dreadneck]

@andrewRneumann
Sorry for the long silence, life came in the way.

I followed your instructions and now the treble pot and bright switch work! =D
However the mid and bass still doesn't do anything.....
I don't get it.. I mean they should work right? I might re-do the ground connection of the mid boost section and see if I can find a better spot for it. But that shouldn't affect bass and mid controls unboosted?

 

[YellowBoots]

But that shouldn't affect bass and mid controls unboosted?

One way or another, that left lug of the mid pot needs to find its way to ground. If it is ungrounded, the tone stack won’t work. Send us a photo of the pots and all the associated caps/resistors/grounds… maybe the sharp eyes here can spot a mistake. It is confusing.

 

[TwoBear]

The grounding you point out is there and in good shape. I'll look for other possible ground errors.

The way the wiper arrow is pointing in the schematic on the bass and mid pots, does that mean it is tied to lug 1?
If it was tied to lug 3, would the arrow be angled differently?

I think you’re referring to how the pots are represented ? When it’slashed through that means it’s open as in a variable resistor. Is that what you’re talking about like the pots in the tone section?

 

[TwoBear]

If this helps then great.