Hey all,

I put together my bluesbreaker recently. It's sounds brilliant apart from the background hiss. There was other noise that I addressed at the start and now I'm down to a bit of hiss. I think that it may have something to do with the presence pot. The pot is a bit crackley when turning it and if you put it up to 9 or 10 it makes crazy noises! I understand it crackles because there is DC across it. I have the negative feedback from the 16 ohm tap going through the resistor that then connects to the presence pot. I was messing around and took off the presence pot ground to see what would happen and when its not grounded the amp seems to be dead quiet. That's what has me thinking this could be the source of the hiss.

Also if I turn down the presence and treble to 0 the hiss is gone. And with the presence and treble turned up the hiss stays even if I turn down the guitar

Anyone have any similar experiences?? Or anyone got any ideas??

 
Thanks guys!

Hi

This is an old post, but I should reply so that ppl can refer to in the future:

a) When doing Marshalls, ALWAYS have the shield (alum, etc) thats on the bottom of the cab.

  ie, when you test it out the chassis, do expect the treble and presence to be noisy. To avoid this, go to the kitchen, (ask mom first) and get a metal tray. You can then put it on the chassis (circuit side up) to simulate the shield.

b) The presence pot (5K with the single cap) will have DC on the pot, and you'd get the swoosh sound if you turn it.  This is normal. Even the 8000 bucks vintage sample will do it.
 
  You can do like the later marshall, ie the pot with cap and resistor, and it wont do this anymore. But it does change tone a bit (you might not even notice it, or even like it). See some of my layouts for this difference.

Thanks!

nik