1987x w/fx loop noise

[leewinn]

I have a 90's 1987x with an fx loop that makes noise similar to having the instrument cable plugged into the amp but not the guitar (sort of buzzing). The amp makes this noise regardless of whether a cable is plugged into the input or not. With vol 2 turned up to around 3/4 the noise nearly goes away. Turning vol 1 up at all makes it much worse. Also, the guitar can still be heard with vol 1 all the way down. I was leaning toward replacing the vol 1 pot but the resistance is pretty much the same as the vol 2 pot (measured from the center leg to each of the outside legs; turned up and down). I measured resistance to ground from the ground leg of both vol pots and came up with .2 ohms. Any thoughts?

 

[ampmadscientist]

I have a 90's 1987x with an fx loop that makes noise similar to having the instrument cable plugged into the amp but not the guitar (sort of buzzing). The amp makes this noise regardless of whether a cable is plugged into the input or not. With vol 2 turned up to around 3/4 the noise nearly goes away. Turning vol 1 up at all makes it much worse. Also, the guitar can still be heard with vol 1 all the way down. I was leaning toward replacing the vol 1 pot but the resistance is pretty much the same as the vol 2 pot (measured from the center leg to each of the outside legs; turned up and down). I measured resistance to ground from the ground leg of both vol pots and came up with .2 ohms. Any thoughts?

The noise is caused by the AC filament supply...
which powers the tube heaters.

Replacing parts will accomplish absolutely nothing. Don't blame the volume controls.

There IS a way to cancel the noise
which involves moving the filament wires away from the audio paths.
A simple modification, which is fully reversible, and won't damage the amplifier in any way.

There are also other methods of accomplishing the same thing.
DC heaters for the first two preamp tubes...(as used by Mesa and others...)
Elevating the heater voltages...

But with my method, there is no permanent modification, and it's the simplest, cheapest method.
That's why I use it.
It eliminates 99% of all buzz noise, from the audio.

 

[mickeydg5]

Lead dress and AC filament wiring was going to be my second concern.

This is a duplicate thread. Check out the other as well.

 

[leewinn]

Lead dress and AC filament wiring was going to be my second concern.

This is a duplicate thread. Check out the other as well.

It is a duplicate. Sorry, I didn't know how to delete it.

 

[mickeydg5]

It was due to heater operation.
Leewinn changed a few components and adjusted the filament balance.