Okay so I've got a Fender FM 212R amp that has a pre-out and power-in jacks. it doesnt really have anything on the knobs so I was wondering if it is possible to attach a head onto it to give it more EQ settings for more options.

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You could possibly plug a PREAMP into the poweramp input on the FM but plugging a head which has a poweramp and preamp will only cause problems. What exactly are you looking to do, I'm a little confused.
yeah, you could run the preamp out/FX send from another amp into your power-in jack, but you don't want to send a powered signal into that poweramp in. Bad things will happen.
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