Only an observation when using an iPod G4 with a Wuzhi Audio ZK-601 mono amplifier using a TPA3118. Firstly the amp works fine with no bad behaviour on startup or shutdown and sounds OK. The odd thing is when the iPod is used as a source with it's volume at max all is well but when the volume on the iPod is adjusted below max there is high frequency noises and hiss. Return to max and all is well. I haven't come across this before with any other amp Class AB, D, T that I've used with the iPod. I've tried other sources such as a phone and a headphone output on another source which do not have this issue so it must be iPod related.
The amp's DC offset was 11mV when cold and close to 0mV when warmed up. The DC offset on the input using the iPod is 0mV at max volume but increases to 100mV+ when the iPod volume is decreased. This is measured at the input terminal block next to the used 3.5mm socket so may not be accurate. The only difference I can see compared to other modules I've used is that this appears to mix the stereo signal to mono.
It's not an issue as this is just a test amp for a mono test speaker that I use but is puzzling.
The amp's DC offset was 11mV when cold and close to 0mV when warmed up. The DC offset on the input using the iPod is 0mV at max volume but increases to 100mV+ when the iPod volume is decreased. This is measured at the input terminal block next to the used 3.5mm socket so may not be accurate. The only difference I can see compared to other modules I've used is that this appears to mix the stereo signal to mono.
It's not an issue as this is just a test amp for a mono test speaker that I use but is puzzling.
