Hi guys,
I have got a small guitar practice amp. Its powered from a typical 19V power brick. Its humming so bad. There are some known issues with these units and its has got something to do with grounding issues. There are couple of suggestions that people have made and have worked for them:
1. Connect a usb cable to the unit and the other end to a properly grounded laptop/computer.
2. Attach a separate cable from the chassis of the unit to the ground pin of the mains.
3. Change the power supply to a ‘three pronged’ power brick.
I didn’t have any issues with the amp out of the box and with in a weeks time the humming began. I used option 1 and connected the USB port to a well grounded computer. It did seem to help at first but then the hum came back. Right now the usb cable remedy is not working. I tried option 2 as well by alligator clipping the chassis to the mains earth and there is no improvement/change on the hum whats so ever. My mains out are properly grounded and I have confirmed this.
I am starting to think that maybe my unit has got a failing component somewhere as the problem kept progressively deteriorating to the point where it is now.
So I was hoping to get suggestions on what to look for.
I measured the resistances between the AGND, PGND and DGND (marked on the pcb). All seems to be well connected. However I did notice that the chassis of the USB port to PGND showed resistance value jumping around before it settled to 0ohms, I am assuming that its error on my side with my probes.
Also I have got a question about the 3rd option (‘three pronged’ power brick) - how does grounding help with noise etc with an SMPS type power brick. I see with SMPS schematics that the ground is not directly connected to anything on the SMPS but sometimes through a Y type cap to com. Is that connection doing the magic?
Anyway I was hoping for more suggestions on what to look for. I have got the unit opened.
Thanks in advance.
I have got a small guitar practice amp. Its powered from a typical 19V power brick. Its humming so bad. There are some known issues with these units and its has got something to do with grounding issues. There are couple of suggestions that people have made and have worked for them:
1. Connect a usb cable to the unit and the other end to a properly grounded laptop/computer.
2. Attach a separate cable from the chassis of the unit to the ground pin of the mains.
3. Change the power supply to a ‘three pronged’ power brick.
I didn’t have any issues with the amp out of the box and with in a weeks time the humming began. I used option 1 and connected the USB port to a well grounded computer. It did seem to help at first but then the hum came back. Right now the usb cable remedy is not working. I tried option 2 as well by alligator clipping the chassis to the mains earth and there is no improvement/change on the hum whats so ever. My mains out are properly grounded and I have confirmed this.
I am starting to think that maybe my unit has got a failing component somewhere as the problem kept progressively deteriorating to the point where it is now.
So I was hoping to get suggestions on what to look for.
I measured the resistances between the AGND, PGND and DGND (marked on the pcb). All seems to be well connected. However I did notice that the chassis of the USB port to PGND showed resistance value jumping around before it settled to 0ohms, I am assuming that its error on my side with my probes.
Also I have got a question about the 3rd option (‘three pronged’ power brick) - how does grounding help with noise etc with an SMPS type power brick. I see with SMPS schematics that the ground is not directly connected to anything on the SMPS but sometimes through a Y type cap to com. Is that connection doing the magic?
Anyway I was hoping for more suggestions on what to look for. I have got the unit opened.
Thanks in advance.