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Laney CP12 Humming ( Not Any More:-)


kodiakblair
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Picked up this Laney monitor for the princely sum of £10 a few weeks back and hoping for some tips on reducing the hum.

Starts as soon as you power up and really only changes when the bass is turned up. It's constant whether there's anything plugged
in or not. XLR makes no difference either. Doesn't appear to get louder when you turn the volume up full.

I know very little about amps so any pointers will be welcome.

Cheers KB

Edited by kodiakblair
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Good Call @morgano

Armed with the knowledge that costing me £10 it was no biggie if I messed up I Googled "faulty power supply capacitors" :)
They don't appear blown or burst,certainly no bulge, they did however move when prodded with the pliers handles.

Gave a push till the hum stopped then fixed them in place. Result :D

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Hmm. You might find it comes back. Possibly is a dry joint that is taking one or more of the capacitors out if the circuit. By moving it you've (temporarily) re-made the connection. If it comes back or you fancy a bit of soldering it might be a good idea to resolder their connections on the PCB.

Edited by morgano
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Yes, this is quite a common thing with capacitors. Being larger components, there is more mass to resonate, and usually being supported by the soldered joints alone, are prone to annular fractures around the legs. This can cause crackles as well as hum as the capacitor connects and disconnects.
These large components are often supported using hot glue, but I find the adhesion to circuit boards fails with time. When reworking these components, I prefer to use silicone rubber sealant, then reflow the solder joints.

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