Hey I have a Peavey Mark IV bass head.

The problem I am having is that the head hisses like a mofo. The hiss is too loud to practice with at low volumes in my house. Wheather I put in the input to Channel A or B the hiss remains.

However, I have noticed that when i plug in the wire into the PWR AMP Input the hiss immediatle goes away, same happens when i plug into the Preamp out/in. When its in the PWR AMP input, I cant use the equilizers and controls on the amp. Is just one sound i get. Currently i have to use that with a eq pedal I have and it sucks.

Also If i am plugged into the normal channels, on the graphic equiler, if i move the "50" slider from the top, it makes a horrible screeching deafening sound. The other sliders work normally. Also when it is in the quiet PWR AMP state, when i movre the 50 slider is only makes this fart kind of quiet sqeuaky sound.

Im wondering what is causing this Hiss? Can it easily be repaired? How much to get it fixed in the store?

Wow no replies...after a month.

Cmon anyone?

Well, it's something in your preamp. Maybe look up a schematic and see if anything is busted or not wired right? Harder than it sounds to find an old schematic though alot of the time.

I think the problem can be caused by capacitors. I'm not genius, but I have your problem n a lesser scale on an old Peavey head and they told me Icould buy new capacitors and something else (Forgot what and can't find the three year old email) to fix it.