As an IEM user and avid gadget lover, I am always have a particularly interest in portable amps. The sub-$100 price range is where I started my amp journey and I am sure it is the same for many others as well. Though I have moved onward to better portable amps at higher price range, I have always had a keen interest in the budget amp development. Over the year I have built up a collection of some of the most popular sub-$100 portable amps (some are review samples given to me and others are out of my own money) so I thought it is a good time to do a shootout between them from the point of view as an IEM user. Note: This comparison is only a subjective evaluation and nothing more than my own personal opinion.
Sources: Sansa Fuze via custom LOD (around 0.5Vrms)
IEM used for evaluation: HifiMan RE0, Etymotic ER4S and Shure SE530.
Amps are all in their lowest gain setting. Volume matched using a SPL meter to ≤1dB via white noise and double checked with a multimeter. They are also RMAA tested (loop-out / loop-in though Tone Well UT24 audio interface with a 16ohm load) but only result of significant will be discussed. Output impedance and power are measured using fixed loads and 1kHz tone. The reference amps used for the elevation are Meier Audio StepDance and NwAvGuys’ O2 (built by JDS Labs), both excellent amps of their own.
Build quality covers not only housing, but also material, design, size, etc – plastic is not necessary rated worst than metal. Functionality is the key here.
Current are measured (volume matched driving fixed 47 ohm and 23.5 ohm load, 1kHz pure tone) to multiple with voltage for power. Most amp have more than enough power for typical IEM, the important point is having enough voltage for high impedance IEM (>100 ohm) and enough current for low impedance IEM (<16 ohm). However, only two typical numbers are covered here.
Calculated from the voltage difference between no-load and a 47 ohm fixed load with a 1kHz pure tone. Less than 1 ohm is best for most IEM as it has the best dampening and doesn’t affect the FR curve of the IEM.
Size and weight comparison. Ratings are given as relative. From Biggest (1/5) to smallest (5/5)
Related to transient. Mainly about the sense of attack - especially noticeable on bass note.
Not related to coloration, transparency is used as the sum of the openness and layering of the amp, which are what essential to produce the depth of the sound field
If transparency is the depth, then soundstage is used as the sum of width and separations. Together, they define the overall resolution of the amp.
[Coloration / Neutrality]
This can be either pure measurement (FR curve) or perceived difference in presentation. O2 will be the main reference here.
Tested using a cellphone receiving call in very close proximity.
How well the amp behaves with hiss prone IEM, mainly SE530.
Odds and ends that are not covered on above.
Out of a full mark of 5 points
● = 1 point
◎ = ½ point
○ = Zero point
i.e. ●●●◎○ = 3½ points
While I do own a few more sub$100 amps, I think those that are included here are some of the most popular among new buyers and thus make the best sense to be reviewed.
(In alphabetical order)
- digiZoid ZO2.3 ($99.95 $119.95, *note 2)
- Electric Avenues PA2V2 ($60)
- FiiO E02i ($30)
- FiiO E07K ($89)
- FiiO E6 ($30)
- FiiO E7 ($85)
- FiiO E11 ($65)
- Fred_fred_2004's 3 Channels Headphone Amp ($92)
- HeadRoom Total AirHead ($99, *note 1)
- JDS Labs cmoyBB v2.02 ($60)
- SoundMAGIC A10 ($60)
*Note 1: I don’t have the Total AirHead, but instead the Total BitHead will step in for its place since the two share essential the same amp section and sound identical when run purely as an amp.
*Note 2: digiZoid has increased the price of ZO2 to $119.95 which means it is no longer a sub$100 amp)
Edited by ClieOS - 1/5/13 at 9:08pm