At 11:14 PM 6/9/02 -0500, Dale Botkin wrote: >On Sun, 9 Jun 2002, Olin Lathrop wrote: > >Well, seems to work OK. Wow, crash course in audio LPF design. I could >even do it with an op amp now (and still may). Something to consider is the output impedance of the bass pickup. I used to build DI boxes for getting musical instruments into PA system mixing consoles and one of the things I learned early was just how sensitive to loading those pickups can be. You may wind up with a whole lot more level if you buffer your low pass filter with a simple 1 FET buffer (source follower or simple amplifier) - input impedance will increase to the value of your gate resistor (1M0 or so) and gain will be just under unity (follower) or about 5 or so (common source amplifier). Almost any N-channel JFET will do - the old standby 2n3819 or any of the J112 family. Just be sure to operate it from your unregulated supply - most JFETs (2n3819) need between 7 - 30 Vdc to operate. You will also need a coupling capacitor between the FET and input of your low pass filter to keep the DC out of the PIC input. One final thing to increase the sensitivity of the PIC's input - consider biasing the input pin to about the nominal threshold voltage of the pin. That is about 1.4 Vdc for a standard pin and 2.5V if it is a schmitt trigger pin, assuming 5V operation. Add the bias network right after the coupling cap but before the LPF so that you don't attenuate the desired signal. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads