Beta Lead Hiss

[Walt-Dogg]

Picked up a Beta Lead a couple weeks ago, has a loud hiss when it idles, amp has been serviced according to previous owner. What could it be? I'm taking it to my tech anyways, I was just hoping someone who is savvy with Sunn TRANSISTOR amps could give me a hint since once I take it my tech it will be there and I will have to way of retrieving it since I'm driving back to OC from Oakland then flying back to Oakland and having amps brought back up in my car once they are repaired.

[Walt-Dogg]

And is it possible that this is caused by a replaced mid potentiometer in channel A?

[loudthud]

What controls affect the volume of the hiss (if any). Does it change when a guitar with the volume control on the guitar all the way down is plugged into any of the inputs on the front panel? Does it change when you plug the guitar into any of the "Line In" jacks on the back of the amp?

[Walt-Dogg]

When there is no input there is no hiss.

My guitar's volume knob does not affect the hiss.

When I am in Channel A the hiss is there.

When I am in Channel B the hiss is minimal (note, both channels engage anyways).

However:

When I am in both inputs the hiss is louder than in either input A or B.

The hiss also gets louder when the distort and level controls on each channel are turned up as well when the master volume is turned up.

Note: I just ran to my basement to try the line in and the hiss is subdued and not sharp and doesn't become terrible when the master is turned up.

[loudthud]

Each channel has an electronic switch in the signal path the turns the guitar signal on or off controlled by the footswitch and which input jack a cord is plugged into. With nothing plugged in, both channels are off. The Mid control is positioned after the switches so if it was creating the hiss, you would hear it when nothing is plugged in.

There are only two ICs in the signal path of each channel between the input jack and the channel switch. One of those is probably creating the noise although it could come from other components. A good technician can find the source.

[Walt-Dogg]

Thanks, I've found a competent technician somewhat local to my hometown and I will make sure he is aware of all of this but he does know his way around Sunn amps. Goes to show just how lazy techs are (Ehem, Craig at Pwrage...).