Block diagrams of I/O

possum

Hi Faber,

In the hopes of better understanding how the I/O is routed through the iPhone headphone jack, do you have a block diagram of what is going on, including grounding ?

I'd like to avoid blowing up my headphone outputs again the next time I try to measure something.

Thanks,

possum

benfaber

possum,

It's not clear what you are hoping to see in a block diagram. Both channels of the headphone out and the microphone input all share the same common return path on the headset jack.

High voltages are not recommended for the headset jack.

Ben

possum

here is how I understand the I/O block diagram for measuring loudspeaker impedance based on your video tutorial.

I'm using the following equipment;

iPod touch 5G with 30pin to lightning adapter
Line 6 Mobile In

one observation with this setup; I'm not seeing the option for (Ch2-Ch1) input, just Ch1 and Ch2 independently.

Would using a power amplifier be advisable to take some current load off the iPod/iPhone/iPad headphone output ?

Are you aware of any iPhone/iPod/iPad compatible USB input devices that have floating inputs ?

Thanks,

possum

possum

Thanks Ben,

It looks like we crossed posts.  Yeah, I figured out the iPhone I/O share a common ground.

It seems like the iPhone is not happy with inputs exceeding 1 Vrms, which also makes using a power amp dangerous if speaker impedance and sense resistor values are not carefully considered.

Do you know of issues with the missing Ch2-Ch1 input option with the Line6 Mobile In and/or iPod touch 5G combination ? 

possum

benfaber

Do you know of issues with the missing Ch2-Ch1 input option with the Line6 Mobile In and/or iPod touch 5G combination ? 

I have seen that sometimes, the difference channel (Ch2-Ch1) doesn't show up in the input channel list when using the hardware you mentioned (iPod touch 5, Mobile In, Lightning adapter). It should work however, if you restart the app and reconnect the Mobile In. I'm still not sure exactly what the issue is that causes this behavior.

Would using a power amplifier be advisable to take some current load off the iPod/iPhone/iPad headphone output ?

You could use an amplifier. You could also increase the size of your series resistor (8.2 ohms is pretty low).

Are you aware of any iPhone/iPod/iPad compatible USB input devices that have floating inputs ?

Perhaps, you could look for a digital input device and use a separate piece of hardware to handle your analog signals.

Ben