Originally Posted by Favelle
So is "bass boost" the same as a hi-pass filter? I just need to know which resistors to use to make the cutoff 17hz or 18hz.
The link provided is the correct one.
The BASH500 amp offers both a signal boost and a high-pass filter, depending on the resistor values.
If your friend purchased the amp from parts-express recently the amp might already have the HPF you want, as a couple of commentors on the site indicate the default HPF is now between 17-18Hz. (see quote below)
Comment from parts-express.com
"The new resistor values on the PE BASH 500w (or at least the resistors that were on my recently purchased amp) are: R17: 25,000 Ohm R18: 68,100 Ohm. These are much more useful that the old values for most DIY projects. The new Fc = 17.36 Hz; Q= .817; Boost peak is at about 35 Hz with a gain of .28 dB; Gain at Fc = -1.75dB"
If your friend's amp doesn't already have these values, you can use the Fc column of the referenced PDF tables to find the correct values. Given you want approximately 18Hz cutoff, you could use the R17=20 and R18=75 for a HPF cutoff of 18.7Hz and a 1dB boost at approximately 27.5Hz (as seen in the 1dB boost table). You could also try the values posted by the commentor, although I'm not sure if the Fc, Q, and boost have been confirmed for those values.