Hi All,
I finally got to power up my pair of Alpha 20s. I'm seeing DC out when applying power to the board. it looks like 12v then down to -3v along with a high pitch noise/squeal that goes away around the same time as the DC voltage. I have audio out put on both boards, but its accompanied by a high pitch that does not go away. I can throw a scope on it later to see the frequency, but not really sure where to start.
I finally got to power up my pair of Alpha 20s. I'm seeing DC out when applying power to the board. it looks like 12v then down to -3v along with a high pitch noise/squeal that goes away around the same time as the DC voltage. I have audio out put on both boards, but its accompanied by a high pitch that does not go away. I can throw a scope on it later to see the frequency, but not really sure where to start.
Sorry you are having trouble. Somehing is not right.
Sounds like an oscillation if you hear a squeal or whine. Please take a DMM (voltmeter) and get out a printout of the schematic and measure the DC voltage with respect to GND all the nodes of all actives (3 pins of all transistors and MOSFETs) and mark up the schematic in red ink with the notes of the voltages next to the respective pin that you measure it. +/- voltages matter so note postive or negative. That is like taking "vitals", an "EKG", and "complete blood work" of a patient who enters the ER with an unknown illness so the doctors can start to determine what is wrong. Take a photo of this and post it. Also the voltages across the large power resistors. Also show some close up photos of the amp from a couple of angles. We will help you debug.
It is time consuming but necessary. Be careful not to short any pins while probing around as you can fry and permanently damage parts that way.
Sounds like an oscillation if you hear a squeal or whine. Please take a DMM (voltmeter) and get out a printout of the schematic and measure the DC voltage with respect to GND all the nodes of all actives (3 pins of all transistors and MOSFETs) and mark up the schematic in red ink with the notes of the voltages next to the respective pin that you measure it. +/- voltages matter so note postive or negative. That is like taking "vitals", an "EKG", and "complete blood work" of a patient who enters the ER with an unknown illness so the doctors can start to determine what is wrong. Take a photo of this and post it. Also the voltages across the large power resistors. Also show some close up photos of the amp from a couple of angles. We will help you debug.
It is time consuming but necessary. Be careful not to short any pins while probing around as you can fry and permanently damage parts that way.