Wansmith Posted February 9, 2017 Share Posted February 9, 2017 Hi Another beginner question. I think its a general hifi question however i'll be using a headphone setup as the example. I have been puzzling over the function of an amplifier and whether/how/why it can improve sound quality at a given volume. The answer will influence my purchasing decision as to whether to get a portable amp. The two scenarios i'm trying to compare are: 1. An Iphone 6s -> a regular, relatively high efficiency headphone (eg the he400s). 2. An Iphone 6s -> neutral amp (eg the Nwavguy O2) -> that same headphone. The Iphone 6s itself has sufficient power to drive those headphones to uncomfortably loud listening volumes. My question is: if scenarios 1 and 2 are volume matched - then will the sound quality be better in scenario 2 and why? The only reason I can think of is output impedance matching - the O2 has a very low output impedance so it is compatible with low-ohm headphones (whereas the iphone 6s may have a higher output impedance and may not be compatible with low-ohm headphones). Are there any other reasons? If not, then I'd conclude that if the iphone 6s output impedance and the headphone's impedance are compatible, then there shouldn't be any reason to buy an amp. Also, why is it generally recommended to increase the volume to 100% on phones/daps (that don't have a line-out) when feeding into an amplifier? Many thanks for any assistance Link to comment Share on other sites More sharing options...
PleasantSounds Posted February 9, 2017 Share Posted February 9, 2017 I'll start with the second question as it is easier When you pass the signal from one device to another, it inevitably catches some interferences which mix with your signal. The receiving device will be amplifying everything it has received - i.e. your signal together with the garbage that has been picked up on the way to the destination. When you increase signal level the interferences are not affected by that - so effectively you are pushing them further into the background. When you use a digital output a different mechanism kicks in but the effect is similar: the attenuation of digital signal is done by dividing the sample values by a given factor. Smaller sample values will be closer to the digital noise that is an inherent property of the digital sound, and with small enough values you will start hearing that noise. And now to the "what are the amps for" question. First let me point out that even if you're not using an amp, you are already using an amp. Your phone or DAP has one built in. It will be perfect for some headphones, tolerable for others and totally useless for another lot. With the most sensitive headphones what you can expect from an external amp is more noise and difficulty with controlling the volume level. There is a group of headphones which will not give you any noticeable return on your amp investment. For others the amp included in your source device may not be sufficient. This is driven by following factors: - Available voltage is limited by the battery. This may not be enough for some higher impedance or lower sensitivity headphones - Even if the battery provides enough voltage, it may not be able to provide enough current (or not quickly enough) - and then the first thing to suffer is bass quantity (as bass requires most of the power) - As you mentioned, output impedance can alter the frequency response characteristic. But not all headphones are equally sensitive to that (e.g. many planars) and even if they are, higher output impedance is sometimes perceived as an improvement - Good amp will have minimal differences between the channels, which will result in better imaging. This is harder to achieve in tiny amps included in mobile phones. - Good amp will have faster transients, leading to more dynamic and more detailed sound - Good amp will have much lower distortions, resulting in better sound clarity and less listening fatigue I am sure this list could be expanded, but that should give you some idea what you could expect from a headphone amp. 2 Link to comment Share on other sites More sharing options...
GregWormald Posted February 9, 2017 Share Posted February 9, 2017 Whether a separate amp will be better for you also depends on: how fussy you are the quality of the separate amp (and DAC, if included) how portable (small, unfussy) you need the amp to be the quality of the 'phones the quality of the music files where and how you listen (eg.--casually on the bus/train on the way to work means the ambient noise and lack of attention to the music may well make any differences inaudible) your available budget 1 Link to comment Share on other sites More sharing options...
Wansmith Posted February 9, 2017 Author Share Posted February 9, 2017 Many thanks for the responses For this i just want to find out what the answer would be assuming I had golden ears, CD quality flacs, a LCD-X (20ohm, 103db/mW) in a silent room and an infinite budget for an amp. Regarding my first question - i guess what i'm really trying to ask is whether adding high quality fancy amp (say a chord hugo in amp only mode) to the chain make a (relatively) bad source (say the iphone DAC->iphone internal amp analogue output) sound any better for a LCDX? I would have thought with things like channel balance - if it is off coming from the iphone jack then wouldn't it be still off if the analogue signal then goes to a high quality amp? And wouldn't things like dynamic range/imaging/detail retrieval be limited by the source signal? In which case - provided your headphones have the right specs to be driven by the iphone jack to good volumes and in a manner such that they aren't current or voltage limited (ie low impedance high efficiency like the LCDX) - then adding a chord hugo (in amp only) to the chain theoretically shouldn't be able to improve the sound qual? Or is this wrong and does the amp somehow "clean" the analogue signal, even when its operating at a volume that could have been achieved by the iphone itself? Re my second question (why put the vol to 100%) - would I be correct in saying you get a higher/better signal to noise ratio with a higher volume on the iphone? Link to comment Share on other sites More sharing options...
PleasantSounds Posted February 9, 2017 Share Posted February 9, 2017 You can't expect that the amp will somehow clean up the signal, but it is possible to get such an impression. The reason is that amps have pretty high input impedance, and this means that your phone would have no trouble driving them in comparison to headphones. So the signal rather than improving will just not deteriorate as badly as it would with a headphone plugged in. If the amp's output stage is more capable, you should get better results. I can't help you with the Chord Hugo and LCDX pairing, as I'm unfamiliar with this combo. Personally I consider Hugo overpriced and it's styling is not my thing, but that's jut me. You may want to check the head-fi.org as both Hugo and LCDX are well represented there. Regarding q2: spot on - I was referring to maxing the signal to noise ratio. Just keep in mind that it is possible to overdrive the amp's input if the output from the phone is too high. This would manifest itself with a heavily distorted signal from the amp even at low volume settings. If that happens just back down the phone's output volume until it gets better. 2 Link to comment Share on other sites More sharing options...
Wansmith Posted February 10, 2017 Author Share Posted February 10, 2017 Great explanation! Much appreciated, I'm feeling way less confused now. Sorry the Hugo/LCDX was just a hypothetical, realistically i'd be looking at some relatively flexible IEMs for portable use, and work my way from there in terms of whether i need something between it and the iphone, but now I have a better handle on whether (and why) I might need (or not need) an amp as well. Link to comment Share on other sites More sharing options...
GregWormald Posted February 10, 2017 Share Posted February 10, 2017 I have both highly efficient IEMs and full closed headphones. Both can be driven by my iPhone 4 and sound OK. Both sound better when using a Headstage Arrow (smaller than the iPhone) when away from home, and even better with a Meier Jazz-ff (ac powered and connected to a pre-amp). The Jazz-ff has been modified by the designer to better suit the efficient headphones--he says it's easily reversed if different headphones are purchased. Both amps have a "crossfeed" circuit which, to me, is essential for headphone listening. When used with the iPhone (not the computer or the full rig) I use the line level out. This isn't often as I like to focus on the music and rarely listen while actually moving and never while walking, etc. Greg 1 Link to comment Share on other sites More sharing options...
Wansmith Posted February 10, 2017 Author Share Posted February 10, 2017 Thanks Greg The current (tentative) plan for the iphone (mainly spotify or tidal 320kbps with some flacs) is some relatively non-bright sounding IEMs that is value for money around the $500 mark (i've read that the Shure SE535 might fit this description) + an OPPO HA-2 dac/amp (if required/warranted after listening tests). Link to comment Share on other sites More sharing options...
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