I am a newbie and this is my first amplifier.
I am in the final stages of building a Pass A75, and I have run into a little snag. I have supplied a signal from my variable headphone on my CD player, from a disc that I made with a 1KHz track. The out put array of transitors is not hooked up. The PCB is from AudioXpress, and is populated per the schematic except for the resistors at the gates which Have been increased from 100 to 220 Ohms. When I apply power to the amp with this 1KHz sine wave, I get a very dirty signal that is full of some oscillations. I tried to trouble shoot this by taking my oscilliscope and probing different areas, here are my results:
1: output=dirty sine wave
2: Regulated+, Regulated- = very dirty DC, which is clean when the amp is not connected.
3: input = also has become very diry.
This shows me that the ocillations are nearly everywhere in the circuit.
What I have tried so far:
1: Increased the gate resistance from 100 to 220 Ohms.
2: included 39pF at C9 and C10
This is moving in the right direction as I have been able to eliminate most of the oscillations. However I'm still stuck with an output that looks like a sawtooth at higher output and a square wave at lower output with oscillations at the peaks. The input seem to have these same artifacts.
Any help suggestions or ideas would be greatly appreaciated because I am really strugling
Cheers,
Greg
I am in the final stages of building a Pass A75, and I have run into a little snag. I have supplied a signal from my variable headphone on my CD player, from a disc that I made with a 1KHz track. The out put array of transitors is not hooked up. The PCB is from AudioXpress, and is populated per the schematic except for the resistors at the gates which Have been increased from 100 to 220 Ohms. When I apply power to the amp with this 1KHz sine wave, I get a very dirty signal that is full of some oscillations. I tried to trouble shoot this by taking my oscilliscope and probing different areas, here are my results:
1: output=dirty sine wave
2: Regulated+, Regulated- = very dirty DC, which is clean when the amp is not connected.
3: input = also has become very diry.
This shows me that the ocillations are nearly everywhere in the circuit.
What I have tried so far:
1: Increased the gate resistance from 100 to 220 Ohms.
2: included 39pF at C9 and C10
This is moving in the right direction as I have been able to eliminate most of the oscillations. However I'm still stuck with an output that looks like a sawtooth at higher output and a square wave at lower output with oscillations at the peaks. The input seem to have these same artifacts.
Any help suggestions or ideas would be greatly appreaciated because I am really strugling
Cheers,
Greg