Review on Tihebeyan Amplifier Channel Portable Digital by Samuel Nguyen

I bought this to add a headphone amp to my main 3 amp system. Upon arrival I checked whether the unit's negative speaker terminals are common or not. We found that wasn't the case, so we included a resistor network to isolate the negative terminals from each other. (The headphones shorted them out and this should isolate that short from the electronics using 2 x 100 ohm resistors.) Then I plugged them in and tested. The amplifier had a high-pitched hum, clearly audible above the signal source. i will return it I don't know if this is a design flaw or just a bug in this particular device, but it's not worth trying to find out.