My D9 Dartzeel clone also runs hot. The cooling fins were around 40ºc after playing quite loud for a few hours. Genuine Dartzeel NHB-108’s are biased to produce their first 20 watts in class-A so it makes sense these clones run hot.
I was able to reduce the interference by 80% in the FM711 by correctly wiring the power supply by twisting AC cables and separating the + & – supplies. The amp originally had all the power supply cabling in straight runs zip tied together. Now I need to place my ear to the speaker where as before I could clearly hear it from my seating position 4m away. Unfortunately there is no possibility of returning these amps to Aliexpress without having to pay return shipping.
After fixing the wiring and adjusting the quiescent current, my initial listening impressions remain the same. It is OK sounding and probably better suited to bass shy bookshelf speakers as they lacked the bass control my Hypex and D9 amps have with my Arendal 1723 Tower THX speakers. That said, I am thinking of adding the power supply caps from the broken amplifier board to the FM711 to raise each channels capacitance from 40000uf to 60000uf to see if that improves its sound quality.
