(Cross-posted to the headphone forum)
I have this portable "hybrid tube" headphone amplifier. The Little Bear B4-X. I adore it, it sounds just to my liking. It runs on battery power, and I generally use it by plugging it into my phone, ipad or laptop. However, it has a flaw. If it is connected to, let's say, my laptop, and then I plug my laptop in to charge, the headphone amplifier produces a fairly loud 60hz hum through the headphones. When I touch the metal chassis of the laptop, or the metal parts of the 3.5mm audio signal cable leading to the amplifier, or the metal body of the magsafe charging cable, the hum immediately vanishes. Therefore, it is only possible to use the amplifier with a source that is ALSO running on battery power.
I'm not knowledgeable enough to know why this might be, or how I could attempt to fix it. Perhaps there is some modification I can make to the device which will solve this problem?
I have tried reinforcing the chassis ground on the amplifier itself, even adding a second lead from the negative leg of the battery straight to the grounding hole on the PCB. Nothing seems to make any difference. I have some experience building audio electronics from kits. I know my way around a soldering iron. So if I knew WHAT to do, I could certainly do it. I found this sub after a search, and thought maybe someone here could help me.
I welcome any input or suggestions. I've attached a picture of the PCB here, in case it helps. Thanks in advance.
I have this portable "hybrid tube" headphone amplifier. The Little Bear B4-X. I adore it, it sounds just to my liking. It runs on battery power, and I generally use it by plugging it into my phone, ipad or laptop. However, it has a flaw. If it is connected to, let's say, my laptop, and then I plug my laptop in to charge, the headphone amplifier produces a fairly loud 60hz hum through the headphones. When I touch the metal chassis of the laptop, or the metal parts of the 3.5mm audio signal cable leading to the amplifier, or the metal body of the magsafe charging cable, the hum immediately vanishes. Therefore, it is only possible to use the amplifier with a source that is ALSO running on battery power.
I'm not knowledgeable enough to know why this might be, or how I could attempt to fix it. Perhaps there is some modification I can make to the device which will solve this problem?
I have tried reinforcing the chassis ground on the amplifier itself, even adding a second lead from the negative leg of the battery straight to the grounding hole on the PCB. Nothing seems to make any difference. I have some experience building audio electronics from kits. I know my way around a soldering iron. So if I knew WHAT to do, I could certainly do it. I found this sub after a search, and thought maybe someone here could help me.
I welcome any input or suggestions. I've attached a picture of the PCB here, in case it helps. Thanks in advance.