what is "farting out"?

[Staccato]

The amplifier ‘fart’ is usually associated with so called "blocking distortion" between gain stages.

This is common when you boost a stages gain too much by some of the following:

-raising the anode/plate resistor value
-upping the cathode bypass cap value
-lowering the cathode bypass resistor value

There's two ways of addressing the problem. Change the PS-the faster diodes (hexfreds) which is expensive, or smooth and slow the transition of the diode (snubbing).

 

[Jeremy Allen]

I'm not trying to be a smart Alex; I'm really looking for some help here. My amp is only distorting on the lowest notes on the E string (~E - A). Above that I just get normal tube compression/overdrive.

That doesn't mean that what you're hearing is "farting," just because Bill's description mentioned farting being heard in the lowest notes and amp clipping being heard higher in the spectrum. A 23 watt amp can't push an Eminence Beta 12 beyond its xmax, as Bill says, therefore no farting there.

What you're describing sounds pretty typical of my experience with low-watt tube amps, and I don't know why it happens. But I've certainly had the same thing happen to me many times, where you get it dialed in so that the overdrive is pretty nice and smooth except for in the very lowest notes, which are really raunchy and different sounding. In my complete non-understanding of tube amps, I just always assumed that the lowest frequencies, which require the most power to amplify, simply push the amp into a strange place. Like if I play a 5-string through a tube amp and don't change anything--my touch and attack--the notes on the B-string and E-string can be pretty distorted when the stuff higher up sounds "normal."

 

[John D]

". . . where you get it dialed in so that the overdrive is pretty nice and smooth except for in the very lowest notes, which are really raunchy and different sounding."

This pretty much nails it. This is an old amp, and it appears to be all original electronically. I'm thinking the power supply is just running out of gas on those lower notes. Maybe it's time for some new caps or possibly a solid state rectifier. I was just looking for some other opinions before I start tearing into an otherwise original amp. Thanks to everyone for your input.

 

[billfitzmaurice]

This pretty much nails it. This is an old amp, and it appears to be all original electronically. I'm thinking the power supply is just running out of gas on those lower notes. Maybe it's time for some new caps or possibly a solid state rectifier. I was just looking for some other opinions before I start tearing into an otherwise original amp. Thanks to everyone for your input.

I agree that this indicates problems with the amp, probably with the power supply. Amps are far more linear with respect to how they handle being overdriven than speakers are. They have to be, otherwise you couldn't get smooth overdrive, with either bass or guitar.

 

[John D]

Thanks Bill. Everyone talks about the smooth overdrive that this amp is supposed to have. Something that ,so far, I have not been able to achieve.