Marshall AS50R

[capnjuan]

I'm an amp rookie. The other night I experienced a loud hum each time I tried to plug the guitar into acoustic channel one. When I switched to mic/aux channel two, it went away. I have much to learn... What am I doing wrong?

Did you plug in with your left or right hand? Tried cleaning the input assembly? There's a mechanical arm inside that makes contact with the pointy end of the instrument cable. Over time, can get layer of corrosion there; squirt in, plug/un-plug 4 or 5 times. Same thing for cable jack at the instrument end - squirt, in/out a few times.

Make sure in amp input jack isn't loose - if it's the type that grounds to the chassis, must make good contact there. Also confirm that end-pin or whatever is at the instrument end has good contact; best can do is snug it up. Could also be cable; poor connections inside the ends; try do-over with different cable ... after clean-em-up. We havin' fun yet? :wink:

 

[Scratch]

I'm an amp rookie. The other night I experienced a loud hum each time I tried to plug the guitar into acoustic channel one. When I switched to mic/aux channel two, it went away. I have much to learn... What am I doing wrong?

Did you plug in with your left or right hand? Tried cleaning the input assembly? There's a mechanical arm inside that makes contact with the pointy end of the instrument cable. Over time, can get layer of corrosion there; squirt in, plug/un-plug 4 or 5 times. Same thing for cable jack at the instrument end - squirt, in/out a few times.

Make sure in amp input jack isn't loose - if it's the type that grounds to the chassis, must make good contact there. Also confirm that end-pin or whatever is at the instrument end has good contact; best can do is snug it up. Could also be cable; poor connections inside the ends; try do-over with different cable ... after clean-em-up. We havin' fun yet? :wink:

Thanks John. Is the a magic formula to volume controls settings?

 

[capnjuan]

Only if your knob goes to 10 ... chances are you won't be able to dial it to 12 ... but while we'ez on the subject and you are in cleaning mode; you need to spray all the controls w/ De-Oxit or CAIG red; the red is especially good for pots because it leaves behind a thin film of lubricant good for the resistive element and the shaft. If you only use the cleaning type, over time it will wash out the little dab of lube on the shaft bearing.

Need to open the amp and spray the fluid in the gap where the three legs show themselves. Spray, turn knob back and forth several times; not just the volume controls, reverb, trem, whatever you have poking out of the control panel.

 

[Scratch]

Thanks again, John. Lubing the Channel one input worked... You da man!

 

[capnjuan]

My pleasure Scratch, I'm glad it was something straightforward and not mischief in the electronics. Once you become in-demand across Tejas, you might want your roadies to look after this every 60 days or so but .... until then, once a year ought to do it. J