So after my last post saying I have not heard or had any RFI/EMI, rebooting or popping issues I decided to play around some more to try and replicate this issue. I still have not had any luck but I have replicated something else. Over the next few days I will be driving about 500km in and out of reception constantly throughout remote Western Australia. I will stack the units and have music playing on my headphones, according to Dennistdk this should do the trick. Until then this is what I have found. WARNING - this is a long post to try and explain it all.
When testing yesterday I noticed something strange when I paused the music and went to grab a coffee, when I got back and hit play it went to the iphone speakers and when trying to choose the output on the phone the Oppo DAC was not in the list anymore. I recalled seeing something mentioned in the threads so went back and read through the last few months.
and you have to click "play" again - and pray the audio goes to the HA-2 and not the phone's speakers).
if i dont press play quick enough i have to turn off (by rotating the volume knob) the dac and back on again to get it to start
This needed investigating. I arranged the following set up so I could switch between them and observe. Please take note of the different input setups A & B.
- Input A - HA-2SE connected to an iphone 7+ (IOS 10.2.1) playing music via Hibymusic
- Input B - HA-2SE connected via USB to laptop and music playing on Foobar using Kernal Streaming plugin
- The other tool I used was a stopwatch for timing.
In each case I ran every test multiple times and the results are exactly the same on each run. In other words it is very repeatable.
When there is no input to the Oppo (output from source is paused), the DAC emits a popping/clicking sound (here on just referred to as pops) at between 33-34 seconds. The closest I can measure is 33.3 seconds but from now on I will just refer to 33s.
- On input A this will occur 33s after the music is paused AND the screen goes to sleep. Mine is set to sleep after 60 seconds so when I hit pause, 93 seconds later I hear the pops. If I hit pause and then 5 seconds later I hit the sleep/wake button I hear the pops 38 seconds later. I have tested this at many different timings and it is always 33s after the screen goes black AFTER pausing.
- On input B it is 33s after I hit pause.
- I believe this popping noise is most likely the amp switching off to save power.
- Before this popping noise is heard you can hit play/pause on input A or B and the result is instantaneous, starting and stopping of the audio on the headphones as the button is pressed.
- After the popping noise is heard and you press play there is a small delay to resume audio on input B (approx 2 seconds).
- Now on input A the same thing happens BUT it occurs after the phone has been woken, not when play is pressed. If you wait the 2 seconds you will hear the pops again (amp turns back on), even though no audio is playing, and if you hit play music resumes instantaneously again. I will assume that something in the apple MFI implementation is communicating to the DAC to tell it to turn the amp back on.
- If you wake the phone fast enough and hit play before 2 seconds is up there is still a slight pause on input A before the music resumes just like on input B. Also like on input B you observe the pause but don't really notice the pops as the music usually drowns it out, unless it is a quite passage like in classical.
- I will put this 2 second delay down as the time it takes for the amp to switch on and occurs when powering the unit on also. (Please note: It may be other parts not just the amp but I would think this is the most power hungry part of the DAC and usually contain switching circuits, which I believe to be the source of the pops).
Now on input A at 33.3 seconds after the screen goes black you hear the pops (amp off), then if you continue to wait, at 182 seconds you hear some popping sounds again, except this time it is the Oppo unit dropping its connection with the iphone.
- If you wake the phone after 182 seconds and hit play, the music plays through the iphone speaker and if you try and select a different output the Oppo DAC is not listed anymore.
- If you wake the phone at 180 seconds and hit play, everything works as described above after the short 2 second delay.
- To note is this is 182 seconds after pausing and timed from when the screen goes black.
- On input B this does not happen, you can leave it for 10 minutes and when you hit play there is only the small amp delay.
- Once the iphone has lost the connection switching the DAC off and back on restores the connection but if you simply unplug the lightning cable from the phone and back in the connection is restored also.
- Surprisingly on the iphone if you keep the screen active and don't let the phones screen turn off (sleep), then not only do the pops not occur at 33s but the connection is not lost at 182 seconds either. The DAC works with instant response and no audio is passed through to the phones speakers. I tested to around 7 minutes to more than double the time when the issue was occurring with no issues.
My take on this. The 33s resume delay is a power saving feature as it occurs regardless of source. The 182 second drop out on IOS after the phone goes to sleep is an IOS bug as it does not occur on my other source, nor does it occur if the iphone is kept active while paused. I will be reporting this to Oppo and also Apple as an IOS bug.
I think the RFI/EMI issues are different altogether and hope I can replicate them to see how and if they fit into this. But I am curious now to know if the 33s pops that occur when paused and screen is off have lead people to believe this is part of the EMI issue. And before people jump on this, I am not disputing this is occurring at all and would love to get to the bottom of it.
If I don't have any luck over the next few days replicated some EMI issues I will put the unit next to some radio antennas at work that transmit signals many times stronger than any mobile could ever achieve to give it a push along
Lastly has anyone been able to recreate the disconnects/reboots due to EMI on anything other than an iphone?