- Jun 20, 1999
I removed the nuts and screws holding the pre-amp board in place on my 250 watt Parts Express amp, but it appears that the board is glued to the rubber gasket, which itself is glued to the main faceplate :frowning: I don't want to damage it by trying to force it. Can someone post a pic of the solder side of the pre-amp board showing the points where the resistors that need to be modified are at? Can I then use a multimeter at those points show in the picture to determine the values of the resistors R26 and R27? The instructions that came with the amp say that the default resistors are R26=56K and R27=120K, for NO BOOST. I'd like to verify those values and add another set of resistors to the solder side of the board to set it up for a Fc at around 20Hz and the smallest boost possible. R26 @ 39K and R27 @ 150K results in a 1 dB boost at 31-15Hz and a Fc at 21Hz, which is close enough. Ron-P said Adire told him that they add a resistor and a capacitor to their 250 watt plate amps to get the desired result, but I'm not sure what the original values are on their pre-modded amps. Help!