Michael B Allen wrote: > On Tue, May 12, 2009 at 5:23 PM, Andy Fierman > <[email protected]> wrote: >> As Anthony has already asked, where is a copy of the schematic? I >> followed your link but haven't found one from there yet. > > Not sure why that didn't work but here's a screenshot of the schematic > in gschem: > > http://207.192.69.113/~miallen/Amp2N5088.png > > Is it customary to post an image or the actual .sch file? >
The format *.png pretty much guarantees that anyone can read it. *.sch requires folks to have quick access to gschem (which probably anyone in this group has) but won't always open as fast on the computer from a web site. The part values are a bit ragged in your png file, hard to say what are dots and what aren't dots. >> For guitar pickup modelling, you might like to do a bit of Googling on >> "spice model guitar pickup" or similar. >> >> The first one I found was this >> >> http://terrydownsmusic.com/technotes/guitarcables/guitarcables.htm >> >> Looks quite useful as a starting place. > > 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. > I don't know much about E-guitars, other than having enjoyed a live rockband here this weekend. But AFAIK the magnetic pickups are high impedance, above 100kohms. Much higher if piezo. Sound cards in contrast are in the kiloohm range so most likely the signal from your guitar collapsed the instant you plugged it into the sound card. Also, keep in mind that sound card inputs often carry a little DC voltage to feed electret microphones. You can measure it with a voltmeter. That can cause a DC current through the pickup coil and saturate the core. 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. Probably the input impedance must be set to a certain value (by means of an extra resistors) so the guitar "likes it" and "sounds alright". -- Regards, Joerg http://www.analogconsultants.com/ _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
