Portaphile Micro Portable Headphone Amp Review

Discussion in 'Headphone Reviews' started by dalethorn, May 13, 2014.

  1. dalethorn

    dalethorn Active Member

    Jul 3, 2011
    Charleston South Carolina
    Youtube review: Portaphile Micro Analog Portable Stereo Headphone Amp review by Dale - YouTube


    Gear used: iPhone5, iPod Touch, iPad Mini Retina, FiiO LOD cables, MrSpeakers Alpha Dog / Beyer DT1350 with T51p earpads / Beyer T51p / Sennheiser HD26 Pro / v-moda M100 headphones.

    Review note: The Portaphile Micro ('PM') headphone amp is a high-level amplifier that's designed to be connected to the headphone jack of portable music players and cellphones, or computers in the case where the user connects a DAC to the computer USB** port and connects this amp to the DAC. In my case, and since the Apple i-devices have a true Line Out (Line Out Dock, or 'LOD') that bypasses the i-device volume control circuit, I run the PM from the LOD using a short FiiO LOD cable. I have not used or tested this amp with a computer using a separate DAC.

    **There are other ways to connect a computer to a DAC, but I mention USB here since it's the most common for small DACs, and portable amps like the PM.

    Setting volume for use with an i-device LOD is simple - the only option is to use the PM volume control knob, which by the way is the most ideal method of controlling volume for music playback. When using this amp from the music player's headphone jack, there will be 2 volume controls inline - the music player's volume control and the PM volume control. In that case I recommend finding a position with the music player volume control that produces clean undistorted sound with full dynamics - not too low and not too high - and then control the volume with the PM only. You could do the reverse of course, but that depends on your particular situation and what might be more convenient for you. My experience with the PM has given me more volume than I need to play all of the above noted headphones to very loud levels, which tells me that clipping or other dynamics limitations are not going to be an issue with this amp.

    The PM comes with a cable that's terminated on one end with a mini-USB plug for charging the amp, and on the other end with two USB-A plugs. From what I read on the enclosed document, the PM can be charged from the included AC-USB adapter using one of the USB-A plugs, or charged from a computer using both USB-A plugs, ostensibly because the amp can draw more charging power from two of the computer USB ports. The PM contains a factory-replaceable lithium battery that has four hours runtime, and approximately 2.5 hours charge time depending on how it's charged. The PM is 4 inches long (including the volume control knob) by 2.5 inches wide by 0.625 inches high. The case is a strong anodized aluminum with nicely-milled end panels attached by 4 hex bolts on each panel, so I wouldn't expect any durability issues, although the volume control knob should be protected.

    There is no particular carry case for this amp that I'm aware of, but I'm using a small 4 x 5 inch zippered leather pouch with it. Some users may be inclined to carry the PM in a pocket while connected to their music player, whether their player is strapped directly to the amp or not. This little amp gets fairly warm when sitting out in the open, but would get too warm I think if enclosed in any kind of pocket when being used. The other amps which I have on hand that are comparable to the PM are the Decware Zen Head and the Electric Avenues PA2V2. All three of these amps are analog only - they require that a DAC ahead of the amp convert the music tracks from digital to analog format. For this review I'm depending on my music player to do that conversion with its internal DAC, but other users may insert an external DAC between their portable music player and the PM, effecting better sound quality by bypassing the music player's DAC.

    Comparing the PM to the $375 Zen Head, I expected the Zen Head to do better, since according to its designer it eschews circuits that can reduce signal quality - reverse-polarity protection for example. The Zen Head is also much larger, allowing the use of more powerful components, and more cost-competitive components that don't have to be as miniaturized as those used in the PM. Still, the tiny PM has a slightly more lifelike sound. It's a subtle difference, but it's good to know that sound quality isn't being compromised by the small size. Normally I'd say that a more lively or lifelike sound is at least partly due to better reproduction of 'air' frequencies, transients, upper harmonics etc., but I didn't get a sense of greater extension or transient response, just a better, slightly clearer sound. So whatever makes the difference is probably in the various high-tech components that Portaphile designed into this amp.

    Comparing to the low-cost (~$70 USD) PA2V2, there was a more obvious difference in sound quality, but I thought the PA2V2 came closer to the tonality of the PM than did the Zen Head. Oddly enough, that may have to do with the extreme simplicity and small size of the PA2V2, since shorter signal paths are better, all other things being equal (although they rarely are). But the PA2V2 amp struggled with the Alpha Dog headphone, and so I had to use the DT1350/T51p modded headphone for that comparison. Even with the more efficient headphone, the PA2V2 exhibited some hardness, clipping, or other electronic/electrical anomalies that the PM did not suffer from. Since the PA2V2 has a plastic case, that probably accounts for some sensitivity to electrical interference that the PM is better shielded from. The Zen Head also has a good metal case and seems relatively free from electrical interference.

    Looking at the PM from the front, there's the 3.5 mm headphone jack, the power-on LED, the low-high gain switch, the 3.5 mm source-input jack, and the volume control knob. The top, bottom, and sides are plain, and on the back are the mini-USB input jack and a recessed charging indicator LED. The following music tracks were my primary test music for this review. Although my i-devices are unmodified and can play only 44-48 khz WAV tracks, there's enough detail above ~15 khz or so from the internal DAC to reproduce the fine harmonics and decay necessary to compare these amps.

    Chromatics - I'm On Fire (Synth-Pop, female lead): This music track has a very spacious sound, providing a pleasant stereo image. The voice and instruments are well balanced and the tambourine sounds very realistic, undoubtedly because of the excellent harmonic reproduction.

    David Hazeltine - Fur Elise (Jazz): A very high-quality recording from HDTracks, where the instruments are reproduced smoothly with a spacious ambiance. The wire-brush-on-cymbal harmonics are very extended and detailed with the PM.

    Jimmy Smith - Basin Street Blues (early 60's): This track has several loud crescendos of brass and other instruments that don't sound clear and detailed with some amps. Listen particularly to the second crescendo at 15 seconds in for maximum detail effect. I'd like to emphasize that these crescendos are probably the worst-case test I have for instrumental separation and detail, and the PM aces them.

    Kellogg Auditorium, Battle Creek Michigan, Aeolian-Skinner Organ - Pedal, 32', Resultant, Arpeggio: This 16 hz organ pedal tone differs from other tones in that you won't "hear" it - you only feel it. Although most music tones have harmonics, the harmonics from this tone are too weak to provide any "feel", so what you actually hear is not part of the fundamental 16 hz tone. There are ~30 hz sounds in the outdoor environment in big cities, generated by large trucks, buses, and subway trains, and they have a quality of "rumble" that's similar to some deep-bass tones found in music. This 16 hz tone is easily distinguished from those sounds when compared using gear that's distortion-free with suitable dynamic overhead at 16 hz. With this amp you can almost count the 16 "beats" per second in this track, since even with harmonics of 32 hz or above, the 16 hz tone is so clearly reproduced in the "feel" sense that the only reason I can't count the beats (peak and trough cycles) is because they're too close together.

    Porcupine Tree - Trains (Pop-Rock): This track opens with some nicely-detailed string sounds and a forward-sounding male voice with a higher-than-average register. There are a series of "clip-clop" effects starting at 3:19 that should sound like they were made with wooden blocks of some kind. The PM reproduces these sounds exceptionally well.

    Richard Strauss (Mester-Pasadena) - Also Sprach Zarathustra (opening) (Classical): The granddaddy of bass is in the opening 1:50 of this recording, and I've heard it only once on a large and expensive loudspeaker system in Cleveland. For most people, that experience would be indistinguishable from being in a fairly strong earthquake. The PM reproduces that experience as well as any headphone amp that I've heard.

    Trombone Shorty - Backatown (Jazz-Funk): The deep bass impacts here are quite strong, and work very well with the horns and other instruments. The PM delivers the impacts with great weight and detail, and the horns have the kind of bite that gives them a wonderfully realistic sound.

    William Orbit - Optical Illusion (Billy Buttons Mix) (Electronic): The string tones beginning at 0:18 are fairly soft but detailed, and while the bass isn't very deep, it adds a solid underpinning to the music. This is a good track for comparing amps because many of the tones and their harmonics are soft and fairly subtle, and with some of those amps the harmonics won't reproduce properly.

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