DOWN THE RABBIT HOLE WITH THE iPHONE 5S I recently upgraded from an iPhone 4 to an iPhone 5S. Previous to that, I had owned an iPod Touch, 2nd Generation. When I moved from the iPod Touch to the iPhone 4, it was a completely positive transition in every way, including sound quality. I used Sennheiser PX100's (1st generation, with the hard case and wiring to both earpieces) with the iPod Touch and I thought the combo sounded good enough and found it to be enjoyable and listenable. Moving to the iPhone 4, I felt there was actually an increase in sound quality. I was completely happy with the changes. For more serious listening, I used my MacBook Pro, Apogee Duet (FireWire version), and Grado SR225's. I discovered and purchased my Duet from Head-Fi back when I first joined in late 2008. I joined specifically to find some remedy to the horrible sound I was getting out of my MacBook Pro's headphone out jack (this was before I received the iPod Touch as a gift). But I digress . . . Fast forward to a few months ago: several things happened at once. I upgraded to the iPhone 5S, I sent my Grado's back to the company for repair since they had developed a rattle at certain frequencies (Grado Rattle = Grattle), I mailed off my iPhone 4 to a friend (well, friend of a friend for transport to London--long story--won't go into it), and I had some kind of an allergy thing going on which caused fluid to build up in my middle ear and which affected my hearing. It turned out to be quite an upheaval in my musical appreciation world! I was getting serious listening fatigue with the iPhone 5S --> Senn PX100 combo, and it definitely sounded different to me--and worse--significantly worse, than the iPhone 4 --> PX100 combo. Which was strange since I had read that there was very little difference between different iDevice generations and that the PX100's were easy to drive, low(ish) impedance headphones. Was it the allergy thing? Was it the medicine I was on to treat the allergy thing? Was it the 5S? And the worst part is that I didn't have any old reference to go back to anymore. No iPhone 4, and not even my Duet / 225 combo, since the drivers were replaced in the 225's and hadn't been burned in yet. Several good things have come out of this tumult for me. First, I've gotten back into this world--headphones, Head-Fi, audio appreciation, etc. Second, I've diversified my headphone stable, which is a very good thing. As much as I liked and enjoyed the PX100 and SR255, I've come to suspect that if you're really serious about your music and your sound quality, you should strive to experience a variety of setups: different headphones, different amps, different DACs--all of it. You don't really know what you prefer until and unless you do that, and you don't really know what is actually there and what you are imagining or mis-remembering until you do side by side A/B listening. It's a journey! It really is. And I don't think there is a short cut. I'm usually quite fond of short cuts, in terms of equipment anyway. I don't like to waste money in pointless middle-steps along the way to satisfaction. It is my fairly strong belief that there are certain economies of purchase when getting into a hobby that are false economies. This very funny blog entry details exactly what I am talking about: http://theonlinephotographer.typepad.com/the_online_photographer/2010/05/letter-to-george.html. And I definitely hold that this still applies to ones headfi journey as well. Except that your ears and your listening facilities are changing along the way as well. It's a moving target. And not only that, it's unexplored territory at first. What do you prefer? This or that? How good is good enough? Are you a "bass head", a "treble head", an accuracy / neutrality guy or gal? You just don't know until you experience the differences. So, this has all been a good thing, in the end. But I have definitely felt like I had gone down the rabbit hole and had lost all references and landmarks, and more importantly, my enjoyment of music! In my efforts to get my bearings again and bring my focus back on my MUSIC again, I ended up purchasing the Etymotic ER-4S, Sennheiser HD595, and, most recently, a JDS Labs C5D Headphone Amp + DAC. TRAVELS IN iDEVICE DOCK WONDERLAND (err . . . that might not be the right term . . . "wonderland") All of the iDevices with a 30-pin dock connector allowed simple access to the line out signal from the internal DAC. You just pluged in a "Line Out Dock" cable (LOD) to the dock and connected the 1/8" stereo phono plug to your external amp. There are a number of high quality, elegant, and convenient LOD cables to chose from. So that's great. But jump forward to the new Lightning Connector (TM) and things become a lot more complicated and a lot less elegant! The Lightning port on your iDevice is a digital only port. There is no direct access to the line level output from the audio codec's DAC. Period. You can buy a Lightning to 30 pin adaptor, and that will have a line level output, but this is because the adaptor has its own internal DAC. I've heard it's "adequate"--on a par with the iDevice's internal DAC--and made by Wolfson. However that may be, what it definitely is, in my opinion, is inelegant. Seriously inelegant and clunky. You've got way too much wide (and double stacked) plastic sticking out of the bottom of your iPhone or iPod, in my opinion. There was no way I was going to go this route, no matter how dissatisfied I was with the iPhone 5S audio codec. (On that note, I have found, personally, that you just need to pair the 5S with the right headphones--see the iPhone 5S section below). And there was no way I was going to double amp my signal. Not so much that I think the effects on SQ are necessarily disastrous, but because if I am going to all the hassle of using an outboard amp, I damn well want to get a high quality DAC along with it in the bargain. So what to do? I learned that there are certain devices that are "certified" (i.e. licensed) devices that work with the iPhone or iPod Lightning port. These are MFi devices: https://developer.apple.com/programs/mfi/. Among them are the CEntrance HiFi M8, the Sony PHA-1, PHA-2, and a number of others. With these devices, your iPod or iPhone is only a transport, sending the digital stream to the MFi device's DAC with a single cable--a Lightning to USB cable. Thus there is no double amping involved, and all the MFi devices I have read about are very high quality (and correspondingly expensive). However, the Sony was out for me due to its high output impedance (10 ohms), and the HiFi M8 was expensive enough to give me pause. I was very tempted to get an M8, and who knows, maybe I will end up getting it at some point in the future. BACK OUT WITH THE JDS LABS C5D However, before I pulled the trigger on an M8, the JDS Labs C5D came along and I learned that Apple had recently enabled UAC1 in iOS 7 for all devices. UAC1 is USB Audio Class 1. It will accommodate up to a 24 bit / 96kHz, 2 channel PCM digital stream, and requires no licensing fees to be paid (and, FYI, there are apps on the Apple App Store that will load and digitally output 24/96 files--Tuneshell is one such app, and there are others). The C5D and other UAC1 DEVICES get their digital stream through the Lightning port output from your iDevice. Straight off the bat, this unfortunately brings up a minor issue that will (and can even now) be solved: in order to connect your iPhone or iPod to a UAC1 device you need a genuine Apple Lightning to USB Camera Adapter cable ($29): http://store.apple.com/us/product/MD821ZM/A/lightning-to-usb-camera-adapter. Note that the micro-USB to Lightning adaptor will not work, as it passes the charging power pins only--no data. So you need a CCK. (People are still abbreviating this as a CCK = Camera Connection Kit, despite the fact that searching on this term in the Apple store will not get you to the right product for a Lightning port iDevice--same idea though, and an easy to use abbreviation, so I will use it also). This CCK cable terminates in a female USB type A socket. In order to connect a C5D or microstreamer or what-not, you must then plug another cable into the CCK cable. In the case of the C5D, that cable is a USB A Male to USB Mini B 5 Pin Male. So, obviously, the minor issue is that this involves two cables and a substantial amount of hard plastic in the middle of that run, where they join. Not great for a portable stack. Two solutions currently present themselves (and I'm sure there are more): 1. If you can solder, buy a CCK, then a DIY USB mini B 5 pin connector. Here is one place that sells such a connector that is billed as being an easy DIY connector with easy to solder pads, etc.: http://www.adafruit.com/products/1389. Or of course, there is always mouser: http://www.mouser.com/Search/ProductDetail.aspx?Hirose-Connector%2fUX40-MB-5P%2f&qs=sGAEpiMZZMulM8LPOQ%252bykzmHhzPuOAFGyJofC62K5Wg%3d. It's Mouser p/n 798-UX40-MB-5P. 2. We here at Head-Fi presume that Double Helix Cables would custom make you a cable similar to this one: http://www.doublehelixcables.com/store/index.php?main_page=product_info&cPath=3&products_id=102, but with a mini-B 5 pin male connector on the end. And finally, more importantly, John at JDS Labs said on his blog that they hope, at some point in the future, to offer short flexible single cables to solve this issue. Now, if you're like me, you're also wondering if this UAC1 functionality in iOS will be broken by some future update. I asked John about this on his blog, and he said, in so many words that while, yes, anything was possible, that this wasn't an accident--that UAC1 is officially supported--and that now that manufacturers have leveraged that capability, it is very unlikely that Apple will brake it. In other words, it's on a par with the A2DP Bluetooth protocol (Advanced Audio Distribution Profile). So personally, knowing this, I'm not worried about this functionality being broken in the future. Introduction But where are my manners! I should back up and introduce the JDS Labs C5D. Here are the unboxing photos: As you can see, it's a classy outfit, this JDS Labs! It's packaged in a very nice box containing the C5D itself, the charging/data cable (both individually packed in anti-static sealed bags), four stick on clear rubber half-dome style feet in a small plastic bag, and with a simple, but very adequate and straightforward instruction sheet topping it all off (instructions are also available electronically on their web site). And here is the C5D out of the static bag: And here is the C5D next to my iPhone 5S: Side view, again with the iPhone on top for size reference: Close-up of the front panel, iPhone 5S on top: And a close-up of the back panel, iPhone 5S on top: Fit and Finish So there she is! And let me tell you this is one beautifully made and designed piece of equipment. Fit and finish are very good indeed--pretty much perfect, actually. The C5D is just beautiful, solid--quality through and through. It's the kind of device that you'll spend time just admiring, turning it over in your hands, this way and that, enjoying how the light plays off the finish and laser printing and the brushed aluminum end plates. Very very nice. And the aesthetic is all of a piece. Nothing looks out of place at all. The whole design and the choices hang together perfectly to create a piece of equipment with integrity and personality. I expected all this would be the case from the photos I saw online, and my expectations were exceeded. I especially love the shade of red that was chosen. Wonderful! And such a nice change from basic black and silver. Not that I don't like black, because I do. I love black. But having the option for some color now and then is a refreshing change. It's why I got a blue case for my white iPhone 5S. Ergonomics The C5D feels very good in the hand and has top notch ergonomics. The three toggle switches (power and bat/chg on the back plate and bass boost on the front) feel solid and precise and snick into place after a decent amount of force is applied with a finger nail. It's just right, in my opinion. Not too hard and stiff a feel, and not too light and flimsy. The switches do not wiggle in the least: they are tight and precise, not loose and sloppy. Wonderful. If you are a violinist, however, or anyone with no fingernail to use on the switches, you will probably feel that they are a little on the pointy side and a little too stiff, and thus less than perfectly pleasant to use. They are really best when actuated by a fingernail, in my opinion. The volume adjustment is another animal entirely, however. Only a very light touch is needed to move the volume lever from its spring-loaded center position. One flick in the + direction (towards the outside of the case) yields a 1dB volume increase. This is barely noticeable--or possibly not even noticeable. Two flicks is definitely noticeable, but quite small. This allows for incredibly precise volume adjustments! And I LOVE LOVE LOVE IT! I am so sick of the huge volume increases or decreases created by just one push of the + or - buttons on an iPhone! I often end up in a situation where one click up is too loud, and yet one click back down to where I was is too soft. This never happens with the C5D. And if you want to increase or decrease the volume in a hurry you just HOLD the lever in the + or - position. After a short delay, the volume will start increasing or decreasing at a nice quick (but not too quick) pace. The volume adjustment doesn't feel "solid", but in this case, that's a good thing! Instead it feels precise and effortless; incredibly easy to adjust, and yet not loose or wobbly in the least. Once you get you used to it, you really start to appreciate it. Or I did, at any rate. It is very functional and capable. And it completely eliminates left / right channel imbalances at low volume levels, such as reportedly plagued the Sony PHA-1, because it is effected by stepped attenuation, not a potentiometer. Finally, if you push in on the volume button when it is centered, you will switch gain modes. The C5D has a "low" gain and a "high" gain mode. If you are driving 600 ohm and/or low sensitivity headphones, you can go into high gain mode for more voltage. For my use, I have not needed to go into high gain mode at all. The click action is nice and definite, but easy to accomplish--which is good because this is a plastic, not a metal, control. !Bravo! on a wonderful volume control, JDS Labs! Well done indeed! The C5D weighs just about the same as my iPhone 5S in its Elago Outfit Matrix case, and slightly less than my iPhone 4 without case. The anodizing (or whatever finish it is) on the case has a really nice feel to it, with just a little bit of texture. When you're holding the C5D around the case, you can feel the edges of the front and back plates which stick up above the case ever so slightly. These are not rounded or soft edges, and your hand will catch on them. They are not "sharp" however--just crisp. Personally, I find this to be a good thing in that the C5D won't slip out of your hand very easily, and the unit is really great size for holding in your hand. Unless you have very small hands, you can easily wrap your fingers and thumb all the way around it and have them touch at the other side. The controls are easy to access one handed, especially the volume control which is in just the right place to be adjusted by your index finger when held with your fingers along the bottom, your thumb along the top and the front plate closest to your index finger. Other orientations, are, however, not so ergonomic for volume adjustments. A Few Nitpicks I will at this point mention a few nit picks with the C5D. First, note what was missing from the box: a USB charger. For me, this was good news. I have too many of the things floating around and didn't need to pay an increased price for yet another one, and I suspect that most of us are in this boat. However, if you do not have a USB charger and don't want to have to charge from your computer, then you should factor in the cost of a USB charger. They're cheap, though, so, no big deal. Also, if you're using this device with an iPhone or iPod, you will need to add in the cost of a Lightning to USB Camera adaptor cable ($29). Again, not a big deal in that most of us would be buying a special cable even if we got a MFi device that could use the Lightning cable that came with your iPhone or iPod. But, you still need to factor this cost in when weighing your options. Another thing missing from the box are any kind of straps or bands to make a portable stack out of the C5D and your transport device. Another cost and item to be added in. And I don't care for the included rubber dome sticky feet. They're too sticky. They look nice and they work well, but they detract from the ergonomics because they feel like someone left a bit of gum on your cherished amp/dac, or like that gummy stuff that holds credit cards to the sheet of paper they are on when they are mailed to you. Finally, I find the included charging and data cable to be exactly the wrong length. At 19" is inconveniently short for charging, and too long for UAC1 data, especially when you add in the extra length of the CCK (about 4" extra). 19" is probably a good length for use as a computer DAC+Amp, however. Unfortunately, the cable is a little bit stiff on top of everything else, and has a ferrite high frequency noise reduction bead around the mini USB end. HF interference noise reduction is good, of course, but the thing is about as wide (long) as your thumb and about as thick as your pinky. Again, not the best for a portable rig, on top of the extra length. For reference here are two photos, the first of my iPhone 5S hooked up to the C5D with the stock cable, and the second of the C5D in charge mode--you can see that the power/charge LED has turned blue to indicate charging. (It turns off when charging is complete). What you can't see is that the C5D in this photo is on a very low tray, to get close enough to an outlet! These, are, however, nitpicks, as the section title indicates, and I mention them to give the complete picture, not because they bother me. Although, personally, I would suggest to JDS Labs that they include a longer, more flexible cable without a ferrite bead on it, since most of us are buying this for portable use and will be modding a CCK cable for data anyway, and thus could use the extra length for the charging situation and don't need a ferrite bead for HF noise reduction. But it's just a suggestion. Functionality There is nothing you need to do to use your C5D on your iDevice or your Mac. It is, literally, plug and play. You should not, however, plug it in or power it up while you have music or sound output in progress. Stop your music or wait for your alert to finish before connecting and powering up your C5D. I always have it powered down before connection or disconnection in addition to having no sound output on my iPhone. When I first connected it to my iPhone 5S, the phone locked up completely. Totally unresponsive. I had to hold both sleep/wake and home buttons to force it to power down. Then, for the next couple of uses after that, I found that the volume control on the iPhone would drop back down to 1/4 on the slider--that it had forgotten that I had raised the iPhone volume to 100 percent. However, since then, everything has worked flawlessly. And, on the Mac side of things, everything has worked flawlessly from the beginning. You need to go into the System Preferences Sound pane's Output tab and select the "C5D Heaphone Amp DAC" but once you've done that, you're set. One important thing to note right away: the volume control on your Mac or your iPhone does *not* disappear. There is a hardware flag that manufacturers can set to determine whether the volume control remains on the device or not. If the volume control does remain, it is a digital volume control, obviously, scaling down the PCM values as appropriate. So it would be unwise to send a very small digital signal from your device and then add even more amplification at the amp stage to get to the same volume. This is why many manufacturers disable this control, having it just disappear. This is the same as having it set to 100 percent. In the case of the C5D, however, I think JDS Labs made the right choice. Mostly because there is no way to know what the volume level is set to on the C5D. No slider, no knob position, nothing. You don't know. And you don't know if it's on high or low gain. So, when I first fire up my C5D, I'm in the habit of lowering the iPhone or Mac volume down quite a bit, just in case. I may get over this at some point soon, but for now, I'm taking no chances that I'll blast my ears accidentally. I've done that before, and I really don't like it! The other reason why this might appeal to people, is, of course, convenience. If you want to tweak the volume you can use either device to do so. But, like I said, keep the volume near full on your Mac or iDevice for best sound quality. Let me back up one step, however! Before you power up your C5D to use with your iPhone or iPad, make sure the BAT/CHG lever is in the "BAT" position. This isolates the USB power rails of the C5D from the iPhone or iPad or iPod. This is very good for two reasons. First, this prevents it from drawing too much power from your iDevice, causing iOS to reject it and block the connection. No worries of that happening here. No need to connect via a USB hub or anything like that. Also, of course, it won't draw down the battery on your iDevice. However, more than that, it functions as a noise isolation as well. There is plenty of noise on a USB power connection in most cases, and it can affect sound quality. This is why there are some people who insist that the connection from transport to DAC and beyond be an optical connection, because it insures that you will not inject extra noise into your audio stream. No worries of that situation here, however! Which is excellent news! And it's why I keep the C5D in "BAT" mode even when listening via my MacBook Pro. I tested it, and it will play just fine while in "CHG" mode, charging the battery at the same time as playing music, but I think I heard an improvement in sound quality in BAT mode--although I could have imagined it--I haven't done any blind testing to see if there really is an effect on SQ. But why take the risk? The C5D battery lasts plenty long enough and then you know there's no risk of extra noise. I should also mention that the feed to the C5D is asynchronous. This means that it relies on its own internal clock to keep the timing of the music stream correct, and not signals from the USB feed itself ("adaptive" mode). This yields a better jitter spec, and is just the right way to go about USB audio according to everything I've read. And, one more thing, UNPLUG YOUR HEADPHONES from the C5D when powering up or down. There is a very loud bass THUNK that gets transmitted through the headphone out jack on powering up or down. It's not pleasant to listen to. Disconnect headphones before moving that power switch. And also, presumably, before moving the BAT/CHG switch as well--but I haven't tried that to see. Not going to. So, let's see. What's left to cover. Ah yes, the bass boost. I'm not going to cover this switch. I hate it. I hate all bass boosts. I love bass. But I hate boosted bass, either electronically or via bass-heavy headphones. It's probably because I'm not only a piano player but also a piano tuner. Having spent years of my life learning to tune and voice pianos, I know what they are supposed to sound like, and boosting the bass most emphatically creates something that does NOT sound right. I know there is a camp that feels that a 6db increase of the bass helps offset the lack of "felt" bass and impact that is endemic to headphone use. But I'm definitely not one of them. For me the one thing does not offset the other. At all. Rather it ruins bass tonality while not replacing that awesome and excellent sense of impact and felt bass from speakers or live instruments. For me it's like trying to cover over the smell of excrement with perfume. Just doesn't work. But that's me. You may be different. If so, the C5D offers you two levels of bass boost via the three position switch on the front panel. Up is no boost. Middle is the most bass boost. And down is the lowest boost. I can't say whether or not it has been implemented well or if it leaves the mids and highs alone, etc. I tried it out only briefly and only long enough to verify that I am not a "bass head" and to wonder why on earth anyone would want such a sound signature. But, hey, personal taste isn't disputable. Just my own preference here. Options are good. If you want a bass boost, the C5D has two levels to chose from. Features / Specs So, I'm going to briefly mention a few of the technical aspects of the C5D. You should really check out JDS Labs blog entry on the C5D for more info. But briefly, beyond the galvanic isolation and asynchronous USB audio, I will mention that the C5D has a very highly regarded "reference grade" DAC in it. The TI PCM5102A DAC, which has its own internal clock, and is capable of 32 bit audio, and which has some impressive specifications. The headphone amp is also very impressive and has a nice low output impedance of .62 ohms. It will put 4.14 volts into 600 ohms, which should be plenty loud enough for most of the high impedance headphones on the market. However, it obviously couldn't drive the planar magnetic headphones that require much more power. At 32 ohms, the C5D will only put 43.6 mW of power into the load. This is a hell of a lot more than an iPhone or iPod, but still far short of what is needed to drive some of the more exotic headphones out there. The CEntrance HiFi M8 is one of the portable DAC/Amp's that would have enough power (plus it is a balanced amplifier), and I'm sure there are others. But for most of us, and certainly for me, the C5D amp section is probably up to driving whatever you throw at it. For example, the Sennheiser HD600 is a 300 ohm headphone with a sensitivity of 102 dB/V. The C5D could drive the HD600's to a SPL of somewhere north of 112 dB. Plenty loud enough. Damage your hearing loud, in point of fact. Sound Quality - First Impressions Ah! So, now on to what's really important! How does the C5D sound? Unfortunately, I haven't had enough listening time to really fill this section out like I want to, and more importantly, my C5D is one of the few that escaped the lab before John found that there was a hum problem and suspended shipments. The problem has been fixed, however, and shipments have resumed--you can read about it on the JDS blog--and my new C5D is en route and will be here very soon. So basically, watch this space. *EDIT* [or rather, the space just below! I copied in text from a later post below these original words] However, what I can tell you is that my first impressions are very favorable, hum and all. Smooth and natural are the words that come foremost to mind. It has all the detail and treble one could want, but absolutely no harsh edges or grittiness. This is not a "digital" sound. I really appreciate it! And, man can this thing drive my Sennheiser PX100's! I have fallen back in love with these little portables. They punch way, way above their weight in my opinion. And they are so, so enjoyable out of the C5D. There is a HUGE difference between the sound of them out of my iPhone 5S and out of the C5D. They sound awful out of the 5S and delightful out of the C5D. My Ety ER-4S's also experience a nice increase in SQ, mostly in the treble--that smoothness and naturalness I was talking about. Not laid back, not forward, not veiled, not edgy, but just a perfect middle point between it all. Accuracy, musicality, ease, precision. I'm loving it. However, I will say that the ER-4S's sound great right out of the iPhone 5S. As I mentioned earlier, I have found that the iPhone 5S is happiest driving higher impedance (but not low sensitivity) cans. The ER-4S (100 ohm), the Sony MDR-7506 (63 ohm), the Senn HD-595 (50 ohm)--all sound very nice out of the 5S. My Grado SR-225's (32 ohm), however, and my PX-100's (32 ohm?) both don't sound nearly as good out of the 5S as out of the C5D. Or I should say that the 225's sound OK and the PX-100's sound terrible. Anyway . . . like I said, watch this space. But so far, I'm very much appreciating the C5D. The hum is starting to annoy me, though, and what's weird is that at first I swear it wasn't present at all. I even called JDS Labs to ask them what the heck they were talking about--hum? what hum? But then, later that day, after charging, when I went to listen again, I heard an unmistakable hum in quiet sections or when on pause. I trust that this problem will be completely eliminated on the modified C5D (they added a single capacitor--see blog.) Sound Quality - Later Impressions OK. Now on to sound impressions of the C5D after I had some quality time with the corrected C5D. JDS Labs sent me a fixed C5D and a pre-paid envelope to return my original one--I happened to be one of the few people who get shipped a C5D before they discovered the initial hum problem. Throughout, I was highly impressed with the customer service from JDS Labs. The new C5D was perfection indeed in terms of noise floor. No hum, no hiss, no buzzing, no nothin'. Just deep black silence. I would definitely not say that I am at all experienced with different headphone amps at this point, so I don't know how worthwhile or relevant my findings are here, but for what it's worth, to my ears, the C5D is clean, clear, precise and pristine. I hear the biggest differences between my iP5S and the C5D in the highs, which are smooth and yet fully present and detailed, and, with my Senn HD-595's also in the bass, which seems "tighter" and more extended. With my Ety ER-4S's I can't hear a difference in the bass, only in the highs. The 5S has a fairly forward or even aggressive high end. It's detailed and resolving and I like it. But the C5D has all the good aspects of the 5S without the bit of edge or harshness that the 5S can impart. It's the kind of thing that's easy to miss with an A / B test, back and forth, but which becomes pretty clear over an extended listening session. It sort of creeps up on you and you realize--wow, that's a beautiful high end! I bought the C5D to be sure that I wasn't missing out by listening straight out of my 5S, and I'm selling it because I don't think I am. Or not by much, anyway. As I said in a post above, if the C5D + E-4S is a 100, then the 5S + ER-4S is a 90 or 95. I thoroughly enjoy my music straight out of my 5S with my ER-4S or HD-595's. Now, this is with the ER-4S's and the HD-595's, both of which have 50+ ohms of impedance. With the Grado SR-225's and the PX-100's there's no contest and there is way more than a small difference between the C5D and the 5S. If I were stuck on either of those two phones I would definitely keep the C5D. Given its specs--especially the low output impedance--I would guess that this thing would work beautifully with most any conventional headphones. It won't add any sort of coloration to or interact with your phones and will almost certainly be loud enough. I highly recommend it if you need a small, portable, high quality, good sounding, powerful Amp / DAC combo. Affiliation For the record, I paid full price for my C5D and have no affiliation with JDS Labs or John, and I was not asked to write a review or anything like that. However, JDS Labs has earned my great respect for the way they handled this hum issue, how they handled my transactions and replacement unit, and for their customer support, blog responses, and phone calls. Clearly this is a great company striving to make a great product, and standing behind that product 100 percent. I had heard this going in, which is why I jumped on the bandwagon from the get go, despite the risks of being an early adopter. I'm glad I got my C5D as early as I did, despite the hum issue. It's a really great unit, and I'm happy to spread the word about the C5D in particular and JDS Labs in general. Cheers! And thanks for reading!