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Topic: iPod Touch 6 has a lower output impedance than iPhone 6 (Read 153 times) previous topic - next topic

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  • pwjazz
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iPod Touch 6 has a lower output impedance than iPhone 6
Oddly enough, I couldn't find any measurements of output impedance for the iPod Touch 6th gen anywhere on the web. It's of interest because according to a note on Archimago's blog, the iPhone 6 has an output impedance of 3.2 ohm, which is high enough to run afoul of the 8:1 impedance matching rule-of-thumb when driving 16 ohm IEMs like the Etymotic HF5 or even a low impedance headphone like the HD 598 CS.

Back in the day, Ken Rockwell published measurements of the iPhone 5 and iPod Touch 5th gen that showed the iPod to have a much lower output impedance (1.4 ohm vs 4.5 ohm). 1.4 ohm stays on the right side of 8:1 even with a 16 ohm load. So the question -- does the iPod Touch 6th gen have a similarly low output impedance to its predecessor?

It turns out that the answer is yes. By my measurements, my iPhone 6 has an output impedance of 3.69 ohm and my iPod Touch 6 has an output impedance of 1.74 ohm. I've never actually done these sorts of measurements before, but my iPhone measurement is in the same ballpark as other measurements I've seen published, so I feel pretty confident that the relative result for the iPod Touch is valid.

I took the measurements using the basic process described by NwAvGuy here.

1. Install Signal Generator by Media Punk Studios from App Store.
2. Generate a 60hz test tone at 0db gain
3. Set headphone volume to 100%
4. Plug a 3.5mm to RCA cable into the device
5. Using a true RMS multimeter like the Janisa PM18, set it into AC voltage measurement mode
6. Get a 0 load reading by touching the negative lead to the outer ring of one of the RCA plugs and touching the positive lead to the male end of the same plug
7. Connect a 22 ohm resistor between the male end and the outer ring of the RCA plug and repeat the voltage measurement
8. Put the numbers into this output impedance calculator.

I did these measurements only on the right channel (red plug). The raw results were:

iPhone 6
------------
Open - 0.508 V
22 ohm - 0.435 V
Output Impedance - 3.69 ohm

iPod Touch 6th Gen
-----------------------
Open - 0.519 V
22 ohm - 0.481 V
Output Impedance - 1.74 ohm