Amp "building up hiss"

[Lowpro]

Alright this seems to me a hard one to describe. My amp actually "builds up hiss" and goes from a quiet hiss to a pretty loud one after about a minute. It does this with any bass I plug in, and with three different cables so I'm sure it's no just a cable/bass issue.

I don't use CFL's and for the most part I've never noticed this until maybe a month ago.

Ideas?

EDIT: Snap I really shoulda mentioned it's a GK1001RBII

[will33]

That'a wierd one. I'd guess some component is starting to go south and is showing itself after it warms up. Can try changing the preamp tube if it has one. If that doesn't work then I don't know.

[wave rider]

Any pedals or whatnot in the signal chain? Passive as well as active basses? Are you using the tweeter management system?

My 1001RBII gets hissy when I push in the Woofer Hi Cut button, I'm running it full range through some Bag Ends.

Will be interesting to find out the answer on this one...

=wr=

[Jeff Scott]

Originally Posted by Lowpro

My amp actually "builds up hiss" and goes from a quiet hiss to a pretty loud one after about a minute.

Camera lenses do a similar thing, only, they collect photons that darken the corners of the image, the cheaper the lens the darker the corners get.

[Lowpro]

Originally Posted by wave rider

Any pedals or whatnot in the signal chain? Passive as well as active basses? Are you using the tweeter management system?

My 1001RBII gets hissy when I push in the Woofer Hi Cut button, I'm running it full range through some Bag Ends.

Will be interesting to find out the answer on this one...

=wr=

RIght I do have pedals but I plugged straight into the amp (with many cords) and still got the buildup. Tweeter and Woofer hi-cuts are off. If I turn on the Mute the hiss geos away, but when I turn off the mute, it comes back (as if I'm muting the hiss itself)

It does this with passive and active basses (my Fretless Jazz does it as well)

I'm really stumped with this one because I've never had it happen with any amp I've owned. I think it must be the amp just because the Mute can "turn off" the noise until I unmute.

[Rafael]

Could be a noisy resistor....they can make white noise....do any of your controls have an effect on the noise? Sometimes by changing the amp settings you can find out where in the signal chain the offending part is....for example, if the input gain has no effect but the tone does, then you can narrow it down to being post-pre and pre-post....if that makes sense!

[T-Bird]

Hi.

Just a component going bad would be my guess.

I'd start with the PS capacitors.

Since the amp sports a FX loop, determening whether the problem lies in the PS, in the pre-amp or in the power amp is pretty easy.

As You wisely included the make and model of the amp, I think the "normal" hybrid amp chip behaviour can be eliminated here. Quite a few amp chips can behave like that when things get nice and hot. As can some discretes if the bias is off as well though.

Regards
Sam

[wave rider]

Have you tried other electrical outlets on a different circuit?

Just trying to eliminate all non-amplifier possibilities...

=wr=