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Man, I wish they had put a level control on the BFD!
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A simple voltage divider with the appropriate input and output impedances would do the job of reducing that high level.
If I assume 50watts across a speaker then the max level at the speaker would be about 20vRMS.
If we want to reduce this to about 2vRMS at the BFD, then that's a factor of 10 (-20dB).
An output impedance of the attenuator of about 600ohms would be fine and an input impedance of ten times that would be acceptable, so a divider factor of 10 would result in a standard resistive value of 5.6Kohm.
The power across the attenuator would be small (E^2 / R =20^2/(5.6K+600) =~65mwatts), so 1/4 or 1/2 watt resistors would be fine.
If you wanted to make it variable from the -20dB down to no output you could replace the 600ohm resistor with a potentiometer of the same value and take the output off the middle leg.
If you need a higher level than -20dB, you could increase the 600ohms up to about 1K, but I wouldn't go higher than that. 1K would be about -16dB down....
level.jpg
Anyway, you could try this and see if it works OK. Play it loud and test the resistors for heat to be sure my napkin calculations are correct... hehehe
brucek