Iphone audio output power: What is the output voltage of the earphon…

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The iPhone 6 is the first non-Android phone to be put onto the Audio Precision APx582 for audio testing. The exact same test tones are used as with Android devices, but they are played back through iTunes at maximum volume. We use the same four static loads as we did with the HTC M8 and Samsung Galaxy S5 for the results you see in the table below.

	15 Ohm	33 Ohm	150 Ohm	330 Ohm
Dynamic Range	84.155 dB	92.281 dB	92.223 dB	92.160 dB
THD+N	5.873%	0.0054%	0.0032%	0.0032%
Crosstalk (L)	-49.608 dB	-56. 239 dB	-71.721 dB	-77.966 dB
Crosstalk (R)	-49.831 dB	-56.459 dB	-72.191 dB	-77.983 dB
Output Power	44.04 mW	26.39 mW	6.614 mW	3.072 mW
Output Voltage	812.7 mVrms	933 mVrms	997 mVrms	1,007 mVrms
Relative Level (20Hz — 20kHz)	±0.088 dB	±0.088 dB	±0.089 dB	±0.088 dB

The first thing to notice is the 15 Ohm load test. At maximum volume, with a -0dBFS signal the amplifier section in the iPhone 6 enters clipping. You can reduce the volume to avoid this, but it does not do as well with really hard loads as the M8 does. You can see the 1kHz sine wave for that below, with the amp clearly clipping at the bottom.

iPhone 6 997 Hz Sine Wave 0dBFS, 15 Ohm Load

For most testing I focus on the 33 Ohm load, as most in-ear headphones have a rated impedance around 32 Ohms. A data comparison to the HTC M8 and the Galaxy S5 is in the chart with the S5 as the clear loser.

	HTC M8	iPhone 6	Galaxy S5
Dynamic Range	92.074 dB	92.281 dB	91.921 dB
THD+N	0.0152%	0.0054%	0.0505%
Crosstalk (L)	-64.780 dB	-56.239 dB	-44.767 dB
Crosstalk (R)	-64. 329 dB	-56.459 dB	-44.804 dB
Output Power	47.63 mW	26.39 mW	10.63 mW
Output Voltage	1.254 Vrms	933 mVrms	592.4 mVrms
Relative Level (20Hz — 20kHz)	±0.664 dB	±0.088 dB	±0.081 dB

Compared to the M8 the iPhone 6 isn’t quite as powerful, but it has lower THD+N and a much better relative level. The relative level isn’t a big deal, as a variation of 0.5dB is unlikely to be heard by most. That the THD+N is 1/3rd the value of that on the HTC M8 is more important, as the FFT below shows a very low noise floor on the iPhone 6 when compared to the one in for the M8.

iPhone 6 997Hz 0dBFS Sine Wave FFT

HTC M8 997Hz 0dBFS Sine Wave FFT

The crosstalk is also lower on the HTC, which is an area the iPhone 6 could certainly improve in. Digging into more depth on the THD+N results provides a bit more context. The HTC M8 has THD+N levels that start at 0.03% but after 2kHz it begins a steady rise up to 0.1% at 10kHz and past 0.2% at 20kHz. In contrast, the iPhone 6 THD+N is 0.03% until 500Hz, rises up to 0.06% at 5kHz, then back down to 0.03% at 9kHz, and peaks at 0.1% by 20kHz. The iPhone 6 will have slightly more midrange distortion but less treble distortion.

iPhone 6 THD+N Ratio Frequency Sweep

HTC M8 THD+N Ratio Frequency Sweep

If we leave noise out of it and look only at distortion then the iPhone 6 does even better. It has a distortion level of -95dB out to 10kHz and then it rises up to -82dB at 20kHz. The HTC M8 begins at -77dB for 20Hz, falls to -95dB until 2kHz, and then rises up to -56dB by 20kHz. The bass and midrange distortion is about equal, but the HTC M8 has far more distortion in the treble.

iPhone 6 Distortion (Noise) Frequency Sweep

HTC M8 Distortion (Noise) Frequency Sweep

Is one phone superior to the other? With the iPhone 6 and M8, I don’t believe so. The M8 is more powerful with lower crosstalk while the iPhone 6 has less distortion and better frequency response. Most notably the iPhone 6 has no results that indicate odd behavior, which we have seen with the Galaxy S5 and other phones. It is a well engineered headphone amplifier provided you do not need to listen to something at maximum volume with a 15 Ohm load.

Can Apple improve this? They could improve crosstalk, though some headphone companies like more crosstalk to help create an image more like a pair of stereo speakers than headphones. They could also support 24-bit audio which can improve on the SNR values here. The test tones are only 16-bit in nature, so the SNR maximum value is around -98dB. The HTC M8 may perform better given 24-bit test tones but would need a retest to verify this. Apple seems to have decided on using Lightning with an external DAC to push beyond 16-bit audio so we will have to wait for devices using that to see.

Audio hardware on phones can still improve a lot to get closer to where the best stand-alone products are. Those are capable of Signal-to-Noise ratios of -120dB or greater, and crosstalk of -110dB or more. How much those would be audible with headphones is uncertain, but when used as a source device with a stereo it may be audible. However, unless high-resolution audio downloads, like Pono or HD Tracks, really start to catch on I don’t see this being a main focus for most of the companies out there. The iPhone 6 is more likely what we will see going forward: good audio quality, but most importantly free of any major issues.

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Apple makes Hi-Fi • Stereo.ru

Complaining about the new times, the grumpy audiophile will certainly remember the iPhone as the source of all troubles and moral decline. We’ll have to shake the charts a bit and prove that Apple sources have been demonstrating exemplary Hi-Fi performance all their lives, to the envy of others.

I remember the reaction of the idle public to Oleg Monastyrsky’s setup. Everyone made fun of his iPhone as a sound source. Have you tried it yourself with a stereo system? Let’s start the review from the most venerable model, which we managed to reach.

iPhone 3GS hit the market in 2009. This, consider, is quite recent for a Hi-Fi component, but today even homeless people disdain to walk with such a phone. And in vain, now you will see. Starting with the 3GS, Apple abandoned the Wolfson audio chips and began to install Cirrus-Logic in its devices — in this case the CS42L61 model, which is also present in the next Quartet and the first iPad. The parting with Wolfson gave some eplophiles a reason to grumble, there are also enough fans of the old-school Classic iPod. Let’s take a look at the RMAA measurements.

Linearity of the frequency response of the reproduced iPhone 3GS. Flatness less than 0.2 dB This graph shows the harmonic distortion relative to a 1 kHz test signal. The arrow indicates the even dominant harmonic

Judge for yourself: the linearity is excellent, harmonic and other distortions are at the level of a normal CD player. On the harmonic distortion graph, the second (i.e. even) harmonic prevails over the others. As the experience of life with tube circuits teaches us, even harmonics create the necessary for hearing good air dissolution. Now it becomes clear the choice of Oleg Monastyrsky and the cases when a model with an analog rather than a digital connection of an iOS device could win in a comparative test of docking stations. But there must be something bad in this phone?

Well, yes, the 3GS has a slightly noisy output (less than 96 dB), it is useless to look for the delights of 24-bit audio on it. You can run such a file, but the DAC will still cut to 16 and bury everything in noise.

The measured voltage at the output of the 3GS is almost 1 volt (this is the standard value for any iOS devices — old and new). If you stupidly switch the inputs of the amplifier between an iPhone and a regular CD source, without adjusting the volume, it will seem that the phone has no chance. But you still try to do everything according to the rules. Achieve the same signal level, and the difference will not seem so overwhelming. But still, the true purpose of the iPhone 3GS is not a rack with equipment, but headphones, and two indicators will be the most important parameters in this incarnation.

The first is the current supplied by the source. Of course, with a high electrical resistance of the iPhone and other headphones, thin smartphones will sound completely liquid even on 64-ohm models — their output current is small and for a normal buildup of a power driver — the one that P = U x I is simply not enough.

To increase the sound output, we need to lower the load (ie loudspeaker) impedance. That is why in the present we have a lot of offers on the market for headphones with an impedance of 16-32 ohms. And this is where the second factor comes into play.

We know from home technology that 4 ohm speakers are considered more difficult to load for an amplifier. Compared to 8 ohm models, these speakers are more difficult to control. To prevent the growth of artifacts, headphones require the lowest possible output impedance from the source. Well, if it is an order of magnitude (i.e. ten times) smaller than the loudspeaker rating. That is, for 16-ohm plugs, the output impedance of the amplifier is desirable in the region of one and a half ohms. Such a value is not found as often as we would like, and the parameter itself is not indicated at all by the manufacturer. And you suffer later, pick up headphones for the player and change cables like crazy.

Therefore, the output impedance of the amplifier will have to be measured independently. This will require a more or less accurate multimeter and an additional piece of cable with a pair of resistors connected in parallel.

We send a technical track to the output (usually it is a sine of 1 kHz at a level of 0 dB) and measure the open-circuit voltage U (xx) at the output.

We repeat the measurement with connected resistors R and we get a slightly reduced voltage U (r) due to the load.

Based on this difference, you can now calculate the source impedance R (out):

R (out) = [ U (xx)/ U (r) — 1] x R

A 3.5 mm laptop or sound card jack can have an output impedance of, for example, 50 ohms. And it doesn’t matter how cool the DAC will be inside there. At such an audio output, thousand dollar 32 ohm armatures will sound worse than Deshwan mugs, which have a nameplate impedance three times higher.

The iPhone 3GS amplifier has just over 2 ohms output, great! So, you can connect low-impedance headphones to it without fear. Let’s repeat our traditional RMAA measurements of the iPhone 3GS under various loads.

As I mentioned above, for this I have several segments with 16, 32, 64 and 300 ohm resistors soldered in parallel. Of course, this is not a 100% imitation of real headphones, since the speakers also have inductance. Do not forget that the passport «4» or «8 Ohm» at the speakers are conditional values. In real conditions, they will fluctuate strongly depending on the frequency. Therefore, this parameter is called «impedance», and not just «resistance», although the measurement values ​​\u200b\u200bare the same — Ohms. But even such a simplified model as resistors in a circuit makes it possible to estimate the increase in distortion when stereo phones are connected.

As you can see, the harmonic and intermodulation distortions have increased several times, but they still look acceptable. By the way, even under such a load, they still remain smaller than pure linear measurements, for example, on the Onkyo DP-S1 audiophile player for solid money.

A frequently asked question on the forum is which portable source to choose? If you don’t have big mugs that won’t play without a good amplifier (read, amperage), then iPhones are absolutely adequate for 16-32 ohm plugs of any price range. At the same time, the cost of the iPhone 3GS itself on the secondary market today is about $30. Do not like the plastic back, take the «four» a little more expensive. You can put some Foobar on these phones for free and play flasks in peace. I don’t know of any other player that can provide comparable sound performance for the money.

More modern iOS components also respect the brand. Brilliant measurements of the iPad mini can be found in one of my past articles. iPad Air shows similar figures, it’s a sin to complain. Although it is not officially stated in any way, but in the iPads and the «six» the measured levels of noise and dynamic range even exceed 16-bit resolution.

Notice how free of noise and other interference the iPad Air’s audio output is. The lower threshold of the signal is below 100 dB, which exceeds the resolution of 16 bits

But we will not linger on them now, but rather we will study in detail the most modern and controversial audio source from Apple. Meet the real champion of hatred — Lightning-adapter A1749, which is equipped with all new smartphones, starting with the «seven».

If the old 3GS today is asking for thirty dollars, then the new (!) A1749 costs a ridiculous nine dollars. Unprecedented money for the DAC / ADC block and headphone amplifier! True, the thin cable of the A1749 is flimsy, but if it is so pathetic, the connection can be protected with a short piece of heat shrink.

Before we move on to the graphs, I would like to admit that out of all the iOS in terms of sound, I liked this module the most for 9 bucks. Even though the iPad family outperforms it in terms of measured dynamic range and noise floor, I enjoyed listening to music through the A1749 adapter rather than the stock iPad audio output. It attracted the property of the so-called «soft touch» (soft touch), with which the first bars of music arose and the stage cloud was built at A1749. Perhaps all this is the merit of the minimum-phase filter, the algorithm of which could be brought to perfection in the latest Apple. And most likely, these are the smallest harmonic distortions and, again, the output impedance, which in the A1749 was reduced to almost a record zero. For low power fittings, this is what Dr. Kurpatov ordered.

Due to the low output impedance, the A1749 adapter performs well even with a load of 16 ohms.

The measurement graphs show that the distortion values ​​do not fundamentally change with the load. True, I encountered a paradox when the nature of the frequency response (i.e. the type of digital filtering) of the A1749changed depending on the iOS source! I did not find a mention of this feature in any tester, usually they did all the measurements on the “seven”. In general, this adapter is a rather mysterious thing. Not all details in it are identified. Some conspiracy theorists have already agreed that this Lightning is not so digital, and even has undocumented analog channels. And the company, as always, remains silent on the details.

For some reason with different iOS sources on the Lightning A1749 adapterchanging the digital filtering scheme. With an iPad, the HF cutoff is below 20 kHz

To begin with, the A1749 will not fit all iOS with a Lightning connector. For example, the iPad mini of the first generation is in flight, and the old “five” works quite well with it. And the shape of the frequency response of the A1749 looks quite typical. But if you connect the adapter to the iPad Air, then the treble rolloff starts much earlier, and at 20 kHz we already have minus 7 dB. And when a signal is applied with a sampling of 48 kHz, everything returns to “normal” again. What is this? A conscious scenario or the result of some internal recalculations due to a mismatch in clocks of the A1749 receiverand iPad transmitter? However, the most imposing drop in the frequency response is demonstrated by another relevant Apple device — the Airport Express modem (MC414/A1392), which we will consider in conclusion.

A neat little module with a green (thank you so much it’s not blue) dot and the most adorable power cord in the world. There are even rumors that some rich people buy Airport Express just for the power cord for other equipment, and the modems themselves are thrown away. We will not do this and will continue the inspection.

On the rear panel of the device, the optical output on the mini-jack is combined with the analog one. Switching occurs automatically depending on the type of interconnect. Airport Express receives sound via Airplay, which means that it works strictly in the 16-bit domain and also outputs sound to the optics in it. It is noteworthy that, unlike portable models, the Airport Express uses a completely different filter, with classic symmetrical oscillation fronts. Another here is the AK4430 DAC, which can also be found in, for example, the Google Chromecast 2 or the Pioneer BDP-440 Blu-ray player.

Airport Express output voltage according to the Hi-Fi standard is 2 Volts. Such a source can be connected to the amplifier on a par with other components without worrying about volume equalization. Which we will do by submitting audio through Airplay. Formally, the mini-jack allows you to connect headphones, but you should not count on the correct sound with them. The output impedance of the Airport Express is over a hundred ohms, which will cause unbalance and noise even with high-impedance models.

The

RMAA shows that the distortion values ​​of the Airport Express, slightly inferior to the rest of iOS, are at a low level. But this is only in formal terms. The figure below shows that the Express, unlike the iPad Air, has a string of small high-order distortion, which may be the reason for the subjective feeling of a boring, «digital» sound.

Comparison of iPad Air and Airport Express harmonics character: confident victory of portable source

The form of its frequency response also demonstrates the Airport Express’s special position, which is completely different from other iOS, including A1749 with its tricks. Some kind of very slow filter causes a blockage of the frequency even long before 10 kHz. Perhaps, to mask compression artifacts, someone loves such pampering, but I don’t really like it. It’s a pity, I would very much like to end this material with congratulations that Airport Express has brilliantly coped with all the tasks. In principle, it did not play nasty, but something prevented me from finally recommending Airport Express as a high-class Hi-Fi source. Or the fault was the nature of the decline in the frequency response with harmonics, or maybe just a high level of jitter, which I still do not have the technical ability to reliably measure.

The digital filter and frequency response of the Airport Express is different from the portable iOS sources

However, it should be said that the Airport Express did not fail and perfectly settled in one of my systems as a wireless digital transport to an external converter. Works flawlessly and calmly outputs HDCD code as well. In principle, an Airport Express line-out would be enough for a normal person, but you yourself understand that for digital preparators, only DACs can be better than DACs.