Controlling howl round with a 'make shift' guitar amp PA system

by Andy Campbell
(UK)

Using an inexpensive dynamic mike (with a rated sensitivity of -74dBV) along with my Fender Deluxe 112 guitar amp results in 'howl round' if I allow the mike too close to the front of the cabinet and still some 'liveliness' when placing the cab in front of me and the mike on a mike stand, with the cab facing the audience - because it is an open back design.

The Fender amp input sensitivity is around 5 millivolts into 33Kohm for 5% output power i.e. 3.25 watts (i.e.5% of the rated 65watts) when both inputs are used i.e one for the mike and the other for my Stratocaster.

The vocal output is only any use if I sing very close to the mike - due to its low output level - I have tried stuffing a large roll of acoustic damping fibre wadding (as used inside sealed baffle speakers cabs) into the back of the Amp and this helps a bit more.

Adjusting the 3 band EQ on the amp - particularly applying plenty of treble cut aslo reduces the feedback but what I would like is a bit more gain on the input with less howling tendency. I tried my Marshall Overdrive Pedal in between and with the OD switched off I get a useful doulbling (6dB) of sensitivity. Does any one have any cheap suggestions, other than the obvious one of screwing a suitable piece of chipboard or MDF onto the back of the cabinet to make it a 'front firing' cab only - which will of course will make it harder for me to 'hear myself sing and stay in tune' whilst playing the guitar accompaniment and will also intoduce an unwanted bass resonance from the excellent 12 inch Fender Spaeker Unit, due to the reduced compliance of the air behind the speaker when in a closed cabinet environment.??



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