- Joined Sep 29, 2015
Hi, I'm trying to build a small portable, battery/walwart powered guitar amplifier. I have a power amp AN7523 chip that outputs 5w from an 12v supply on a breadboard, is a single supply chip a with a max input voltage of 14v. Been trying various preamp circuits, with some success. But so far, yet to hear that magic sound. All my attempts have worked but a bit dull, or overly bright when certain strings on the guitar are strummed.
I'm trying to modify this circuit for a Marshall Mg10 amp that runs on +-15v dual rail supply. I am trying to get the circuit to function on single 12v supply to fit my power amp. I'm especially interested in this circuit because it uses a sallen key filter at the end of the preamp. I'm keen to explore what effect that will have on a preamp.
Using 2 caps and 2 identical value resitors I created 12v - 6v (vdd/2) - Virtual gnd supply on my breadboard and arrange so that one side of my bread board has 6v/gnd, and the other has 12v/gnd rails.
I have breadboarded the first 2 stages , and tried feeding a Vdd/2 voltage supply to the non-inverting inputs of both stages, through a resistor. I just get squealing noises and oscillations, and the output voltage seems to pulse the power amp.
I checked the voltage from the output of the first stage, it seems stable and measured at roughly the same voltage as the vdd/2. The second stage seems to have aglitch, but I don't where.
I have also tried this as inverting stages...I get some signal, but not very stable as well..
Can anyone give some pointers on the types of calculations that need to happen here?? I'm pretty clueless and come to a deaend. and can't directly find much information about "converting" circuits..it must happen, but obviously not very often :