Marti K
02-17-2008, 09:45 AM
I recently acquired a Mesa Boogie 2C combo in great shape off Ebay. When it arrived I fired it up and found that the amp has a very audible hum that's tied to the Master Volume knob.
Symptoms include:
1. Master 1 volume - as the M1V is turned up the hum increases exponentially. By the time the M1V is on 3 you can hear it from 20 ft. away and it gets more obtrusive as you turn it up more.
2. Channel 1 volume - the setting of this pot has no effect on the hum and in fact seems dead quiet.
3. Lead Master - when the lead channel is engaged the amp exhibits a fair amount of added tube rush which masks some of the hum, but its certainly there under the signal. Increasing the Lead Master adds more hum.
4. Lead Drive - Adds a little bit of hum to the signal but not as much as either of the masters.
5. Presence Control - the presence control definitely adds more hum as its increased. I've been playing with it set at "0" for that reason.
So far I spent a bunch of time last night replacing a tube, firing the amp up, listening, then restoring it and moving to the next tube. I did that with every one of the 5 preamp tubes and also the 2 power tubes but it didn't change the hum one bit. FYI this is not a faint sound but extremely obtrusive. To give you a reference there's no way this could be used for recording at any volume and in fact with the volume around 2.5 and nothing plugged in the buzz is easily audible from 20 ft away.
Since the hum is partly tied to the Presence knob is it possible that the issue is a bad pot on the presence knob?
At any rate, any sugggestions anyone out there can offer will be greatly appreciated. I love the sound of the amp but need to get this dealt with before it can be of any real use. Thanks very much.
Marti K
Symptoms include:
1. Master 1 volume - as the M1V is turned up the hum increases exponentially. By the time the M1V is on 3 you can hear it from 20 ft. away and it gets more obtrusive as you turn it up more.
2. Channel 1 volume - the setting of this pot has no effect on the hum and in fact seems dead quiet.
3. Lead Master - when the lead channel is engaged the amp exhibits a fair amount of added tube rush which masks some of the hum, but its certainly there under the signal. Increasing the Lead Master adds more hum.
4. Lead Drive - Adds a little bit of hum to the signal but not as much as either of the masters.
5. Presence Control - the presence control definitely adds more hum as its increased. I've been playing with it set at "0" for that reason.
So far I spent a bunch of time last night replacing a tube, firing the amp up, listening, then restoring it and moving to the next tube. I did that with every one of the 5 preamp tubes and also the 2 power tubes but it didn't change the hum one bit. FYI this is not a faint sound but extremely obtrusive. To give you a reference there's no way this could be used for recording at any volume and in fact with the volume around 2.5 and nothing plugged in the buzz is easily audible from 20 ft away.
Since the hum is partly tied to the Presence knob is it possible that the issue is a bad pot on the presence knob?
At any rate, any sugggestions anyone out there can offer will be greatly appreciated. I love the sound of the amp but need to get this dealt with before it can be of any real use. Thanks very much.
Marti K