Unwanted Harsh Distortion Please help!

GloriousTone

Member
Messages
8
Hi everyone,

I’ve got some really crappy terrible distortion coming from my normally smooth and glorious Mesa Boogie Mark III. It almost sounds solid state in its distortion - crapharsh. I use PAF, low output humbuckers.

I’ve changed all the tubes and it still persists.

I believe it’s coming from the preamp, because when I turn up the master it doesn’t get worse. When I turn my guitar volume knob all the way down to ~10% it’s okay clean, but as soon as I increase the volume it begins to have this harsh distortion. I run my boogie with the volume at 8 and master anything above 2 for those Santana type tones. Put a boost on and it’s completely crapping out.

Since I changed every tube in there I’m confused. Any ideas or suggestions?

Thanks for your time.
 

macrossgeorge

Gold Supporting Member
Messages
915
Are any of your tubes redplating? Do any of them look like molten lava? If so then turn your amp off and take it to an amp repair person. This happened to one of my amps recently, really harsh distortion tone, looked around back and 2 of my 4 6L6 tubes were molten. Just got it back from the amp tech today.
 

GloriousTone

Member
Messages
8
Good idea, I’ll check that tomorrow morning when I get back to it. Thanks for the tip.

I would be surprised though, because the sound doesn’t get worse when I turn up the master. You’d think cranking the master would make it completely crap out, but it doesn’t. In fact it might get slightly better because it starts to distort and smooth off the harshness, which may be coming from the preamp.
 

jaxjaxon

Member
Messages
395
It may well be the Tubes Bias is set to high. Drop the bias voltage and you will get less distortion. Same applies to the power tubes drop the bias voltage less red plating. And your tubes will last longer biased for less voltage.
 

Silent Sound

Member
Messages
5,123
You're right that it's probably in the preamp. But where is not going to be easy to find out without experience and the right tools. This is tech time.
 

V-man

Member
Messages
2,712
If tubes are ok (condition/bias) it could be an op amp if in the circuit. I recall a marshall that suffered the same until the channel was switched out of the op amp’s path.
 




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