One oldie circuit from local electronics mag that I rescued from waste paper some 25 years ago. This is a buffer/preset volume switch, using jfet as voltage controlled resistor. I dont remember seen anything like this elsewhere. Hope the author does not mind me posting it. Maybe I´ll remove it soon anyway. The darlington preamp/buffer is connected to 4,7 k pot, which is does not much do nothing when jfet is in high resistance, but when jfet goes low res it is part of voltage divider. Caps and resistors at jfet gate remove any plops and clicks. Freewebs does not allow link from another site always so maybe you have to type or copy/paste the url.
http://www.freewebs.com/nassetronics/testin2.htm
The second example of old hobbyist circuits for guitars is from late sixties I quess. It is a "almost" passive 7 band tone control "Multi Tone". Original idea is told to be some Ian E. Ashdown, no other info who and where he was. A local magazine published this circuit which is based on idea somewhere else. "BM-1" refers to ready-made preamplifier module, and is best replaced with some other input buffer and preamp stage. I think this kind of eq might be difficult to use, because lots of knobs, and not so steep filters interacting. Filter freqs are said to be 75, 150, 300, 600, 1200, 2400, 4800 Hz
http://www.freewebs.com/nassetronics/vintagecircuit.htm
I'm still trying to figure out what the 9v battery in the Multi-tone is for. :?
Quote from: Mark HammerI'm still trying to figure out what the 9v battery in the Multi-tone is for. :?
It's for powering the BM-1 preamp module. :) I imagine that network of resistors and caps is a real impedance nightmare so a buffer of some sort would be mandatory.
Take care,
-Peter