I’ve just returned from a long odyssey into the wilds of iPhone-friendly portable DAC/amps. I was first introduced to the concept via the Sony PHA-1 at a head-fi meet in Troy, MI, by
@jude, which used a clever hooked strap that caught rails on the side of the DAC/amp to hold on the iPhone. My with and without comparisons revealed an improvement with the PHa-1, and I became inspired to find the ultimate iPhone DAC/amp.
Sony PHA-1 DAC/amp with hook-on rubber straps for iPhone
I then became briefly enamoured with the V-MODA VERZA with slide-on METALO case for the iPhone 5S, originally designed by Venturecraft. The sound improved very imperceptibly, and the mounting, though clever in concept, was brittle in implementation — the aluminum METALO case would wear down the tabs that made its mounting rails, and a warranty replacement produced an equally fragile case. Like the Sony, it had the advantage of providing a volume control at the top, so you can adjust the volume without taking it out of your pocket.
V-MODA VAMP VERZA DAC/amp with METALO case holding iPhone
Being a fan of the CEntrance HiFiM8, I became intrigued by their HiFiSKYN, which enclosed the iPhone in a case that had about 1-1/2” of extra length (and 1/2” of extra thickness) added to hold a great DAC/amp circuit. I bought one, found that it too had its brittle problems (on/off switch failed and I had to have a repair, which really resulted in a replacement). Its sound was better than that of the V-MODE VERZA. However, it relies upon the volume control on the side of the iPhone, which become buried under undersized access holes in the case.
CEntrance HiFiSKYN envelopes iPhone with a longer, thicker case.
I also discovered the Beyerdynamic A200p, which is a 1-1/4” square 1/2” deep postage stamp- sized case that you can mount on your belt near your pocket and place the iPhone into your pocket. This unit gives great control of the iPhone’s playing, as it has a large volume control and play/pause/repeat/skip controls, all on the case on your belt. I still have one that I use, and it is my second favorite solution to the iPhones DAC/amp problem. However, it requires a Beyerdynamic proprietary cable at the unit to charge from a USB wall charger.
Beyerdynamic A200p mounts on belt and provides volume/transport controls
I loved the sound of the PHA-1, though I didn’t care for its (brittle) method of hooked straps to hold the iPhone (they often sprung loose with surprising elastic throw as you scraped them in putting the unit into your pocket.). Hence, upon the purchase of a pair of balanced headphones (Sony Z7), I bought the Sony PHA-3, which replaces the hooked strap mechanism with a pair of around-case traditional rubber bands. Much better, with great sound and robust mounting, though the stack of PHA-3 with iPhone was too thick for my shirt pocket. This Sony, as well as the PHA-1, have an output impedance of 10 ohms, which alarms the purists that believe that the output impedance of the source should be less than 1/8 that of the headphones (since I use 32 ohm Grado headphones, a 4 ohm source impedance is the maximum).
Sony PHA-3 offers great sound, balanced output, and robust mounting, but is thick
Finally, I arrived at the Oppo HA-2SE, and here I will remain. The HA-2SE has gorgeous sound, a volume control knob that pokes out of your pocket for easy access, a very thin profile, and like the Sony PHA-3 uses traditional rubber bands to attach the iPhone. Like the CEntrance and the V-MODA, it can charge your iPhone in a pinch. It looks fabulous with its leather sheath and brushed stainless metal. It has a low output impedance, unlike the Sony units, suiting it for Grados and other low impedance headphones. It is The Best!
My ultimate solution - the Oppo HA-2SE - svelte, beautiful to ear and eye.