Bass Boost on MCM 250 W Plate Amp (1 Viewer)

[Jim A. Banville]

Okay, I made a visual (color bands) and measured (multi-meter) reading of my resisitors. They are R26=56K and R27=120K, which is no boost. Does this mean there is no rumble filter? The paper with my amp says that for a 1dB boost at 20-24Hz and a rumble filter at 14Hz, R26=56K and R27=220K. I am building a 12" Shiva vented sub and I don't want it to get damaged by trying to produce ultra low bass. I can either go with a 1 dB boost between 20-24Hz with an Fc at 17Hz, or I can go with a 1 db boost between 31-35Hz and an Fc at 21Hz. It seems like it would be a whole lot easier to add some resistors on the solder side of the board to get the final values, rather than removing the originals (the added benefit is that if I every sell the amp, the new owner can just clip out the added resisitors to get a flat response). Can someone tell me what value resistors to add to the original resisitors to get the values for the 17Hz and 21Hz rumble filters referred to above?

thanks!

Jim

 

[Patrick Sun]

*Chuckle* I thought of this thread when I read the post above.
Rtot = Ra*Rb/(Ra+Rb) (if Rtot is less than Ra)
else, add Rb to Ra to get Rtot (no parallelling is possible)
Rtot = final resistor value desired (based on the Parts Express pdf file on the bass boost write-up).
Ra = current resistor in place (i.e. R26=56K)
Rb = resistor needed to create Rtot value
Rb = Rtot*Ra/(Ra-Rtot)