2009/5/12 Joerg <joerg...@analogconsultants.com> > >> For guitar pickup modelling, you might like to do a bit of Googling on > >> "spice model guitar pickup" or similar. > > > > Yes, that is a very interesting page. This is precisely the kind of > > thing I'm interested in. I had no idea the capacitance of the cable > > was so significant. > > > > Anyway it looks like their AC generator is using 2mV. So the 20mV > > value I used to get a good output SIN looks closer to reality which > > means my model is probably ok. > > > > I wish I had a real oscilloscope to find out what my guitar is really > > putting out but xoscope doesn't seem to produce voltages (but I'm not > > surprised since the sound card is probably oblivious to such things). > > Maybe I'll have to get one of those PC oscilloscopes. > >
Unless you are building a pickup, don't get too hung up on modelling it - it's a complex and changing impedance across frequency (stray and interwinding capacitance, leakage inductance, DC resistance etc) and the unit-to-unit variation in impedance and output voltage is large. You've already spotted that cable capacitance plays a part - the tone and volume controls loading the pickup are probably just as important. The trick is to use a high impedance amp front end that isolates the pickup from the rest of the circuit (JFET or, my personal preference/prejudice, a valve triode stage); then you can simplify the pickup model to a simple generator without worrying too much. In my amp work, I use a 100mV pk nominal signal - this is recommended by Kevin O'Conner in his excellent Ultimate Tone series of books: http://www.londonpower.com/catalog/index.php?cPath=3 However, modelling can only get you in the ballpark of gain staging and frequency response - eventually you have to evaluate with your ears, not with SPICE! > > If you want to display the waveforms or an FFT spectrum on the PC > cheaply you could use an emitter follower as a buffer so the voltage > gets transferred 1:1. Then a high input impedance is provided to the > guitar even if you connect a sound card. Agreed, guitar into soundcard is sonic disappointment but JFET source follower would be much better. Here's a good one (not mine, but derived from a Win Hill circuit he posted on Usenet): http://www.ciphersbyritter.com/RADELECT/PREJFET/JFETPRE.HTM Cheers Gareth _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user