THE BIG CONVENTIONAL, SINGLE ENDED AMPS: SR-71A, IQUBE, STEPDANCE, P4 WARBLER
Against the backdrop of the tiny and slim, and balanced amps with fancy volume controls and rechargeable batteries, I have decided to include some single ended amps that are great performers in their own regards, and yet we would love to hear how they compare when pitted against the slim amps and the balanced amps.
RSA SR-71A ($450)
The SR-71A was the first portable amplifier that really took my breath away, and it still is even now. Ever faithful to the signature of the RSA amps, the SR-71A delivers such a level of bass impact, soundstage performance, and resolution levels still unequaled even today. A good resolving IEM like the Etymotics ER4 would reveal the amazing level of resolution the SR-71A has. The Pico Slim manages to match its resolution and articulation, but that’s about it. Plug in a HD650, and you’ll be truly amazed at how hard the bass hits from the SR-71A. Almost everyone I know who’s heard the SR-71A were very impressed with the sound. If you peek inside the SR-71A, you’ll find that the amp has very minimal amount of circuitry, with the two 9 volt batteries occupying most of the space and four massive capacitors (by portable amplifier standards) visible from the battery compartment.
One thing that left a long lasting impression with the SR-71A is the way it does bass. It gives you the hardest, fullest, deepest impact I have ever heard on a portable amplifier. The bass is so awesome, it will rival a lot of entry level desktop amplifier (and probably beat many of them). If you have a lot of passion in this hobby, then the SR-71A is a must to audition amplifier. I also had the Lisa 3 amplifier previously, and even with the bass boost knob, it fails to match the SR-71A’s bass impact and depth (the bass boost primarily adds bass quantity).
Another impression that I get from the SR-71A is the desktop amp-like resolution, which actually betters a lot of desktop amps during its days. Now I can find tiny amps like the Pico Slim, ALO Rx, or the TTVJ Slim easily challenging the SR-71A’s resolution, but the SR-71A was really impressive during its days, and still is one of the best in terms of resolution today. To add to the awe factor, the soundstage is wide and deep. Not as wide as the latest portable balanced amps, or the ALO Rx, but the SR-71A still betters them in terms of depth, imaging, and center image. To top everything off, the SR-71A happens to come with a warm and pleasing tonal balance that is still one of the musical sound I find on the portable realm.
Evaluated as a whole package, the SR-71A is indeed quite a dinosaur. Not only due to the size, but for the lack of “technology” embedded in it. In this case, the lack of a rechargeable battery is a big turn off. If you use the amplifier sparingly, like 1-2 hours per day, then it can probably last through one full week. But if you constantly run that amplifier during your work hours, then expect to do a battery change every day. And that means “painstakingly” unscrewing the back plate, replacing the batteries, plugging the old batteries to the charger, and screwing the back plate on. It’s a ritual that I have to live through during the many weeks that I listened to the SR-71A for this review. And though it was not a big deal before the dawn of the everything-rechargeable amplifier era, it is a big deal now. No wonder my friend Peter barely uses his SR-71A even though he’s a big fan of the RSA sound. Now, if Ray Samuels can release an SR-71A with a rechargeable battery (and throw in a digital volume control as well), then we have a serious new contender in the game.
I-QUBE (€399 V1, €499 V2 with DAC)
Being the only digital (Class-D) portable headphone amplifier certainly makes the i-Qube a unique amp. Come to think of it, I don’t think there are any digital headphone amplifiers even on the desktop set ups. Class-D topology is very power efficient (i-Qube claims 90-95% power efficiency), and so it should be a rational choice for portable amps. The Class-D topology is still viewed with much skepticism among the audio circle, as some design limitations of the switching topology still prevents Class-D amplifier to reach the same sonic performance level you get with tubes or transistors.
The i-Qube is a unique, specialty amplifier. And even now, the i-Qube fans still consider it to be irreplaceable even as the abundance of newer amplifiers come in. The sound of the i-Qube is inherently very clean and noise free. Going back and forth between the i-Qube and say the SR-71A is like comparing a film-based photograph to a digital one. The digital photograph is likely to be far cleaner in noise levels, and that is what I am hearing through the i-Qube. In fact, all the other amplifiers in this comparison would sound grainier relative to the i-Qube. The grain free sound makes instrument detail very noticeable and instrument separation very good as well. Since the instrument detail is evident through the lack of noise in the sound, and not by some upper frequency boost, the i-Qube are very unoffensive and is good for long term listening.
As good as the i-Qube may sound on the previous paragraph, people who has heard the i-Qube eventually come out with mixed impressions. Often the comments would be something along the line of “The clarity is very impressive, and so and so, … but there is something about the sound that I find to be …”. Indeed the use of switching topology does come with its own drawbacks. Proponents of conventional amplifier topology often describes the Class-D amp as lacking impact, or grunt. This happens to be one of the issue of the i-Qube. Though you get a well defined bass, but punch and impact factor seems to be very weak, and it’s not a case of under-amping either, as I still find the same issue with IEMs where the conventional amps can drive the bass with more authority than the i-Qube. Other factors like the timbre, ambiance, or decay of the instruments through the i-Qube is also quite different than on the non Class-D amps. But for most people, the biggest factor would be the lack of impact in the bass, which in turns leads to a very low PRaT factor. It’s probably not an issue if your playlist consists of Smooth Jazz, Unaccompanied Cello, or Enya, but for most of us, the limitation on the PRaT is going to hold us back from getting the beat in the music.
The i-Qube remains unique enough, however, that if you’re serious enough into this hobby, I would recommend you to include it in your must-to-audition list. It’s not going to be everyone’s cup of tea, but some people I know consider the i-Qube to be irreplaceable, and I’d have to agree with them.
CORDA STEPDANCE ($370)
The latest portable amplifier from Meier is all about clarity and articulation. The sound definitely resembles the bigger Concerto desktop amplifier, though based on a different op-amp (AD797 on the Concerto vs OP1611). The similarities extend to the use of the active balanced ground that’s also employed on the Concerto, as well as a relay based volume control. During my time listening to the the Stepdance, I can’t stop thinking about how similar the sound was to the Concerto, and how Meier is moving away from the warmer sound found on the older Cantate, Opera, or Headsix/2Move/3Move models. The new Meier sound is about clarity and articulation, and the Stepdance is truly faithful to that description.
The new Meier sound improves on things like bass control, which was significantly looser on the older 3Move/2Move/Headsix, and the improved clarity is noticeable across the frequency range. However, the sound is also noticeably thinner and drier when compared to the older Meiers, and also the other amps in the group, especially in comparison to the darker sounding RSA or Headstage amps. Even paired with dark and warm headphones like the HD650 or the JH16Pro, I can still detect some dryness in the midrange, though I’m loving the superb bass articulation. I also took the Stepdance and compared to the Ibasso line and the HeadAmp Pico amps, which are less dark sounding amplifiers than the RSA group, and even then the Stepdance still sounds noticeably thinner and drier in the mids and lows.
I tried pairing the Stepdance to the uber-Basshead ATH Pro700 Mk2, and the Stepdance was able to create some very solid definition on the otherwise textureless bass of the Pro700 Mk2. The Pico Slim does this to a similar degree, but obviously the Stepdance has higher power level to take a hold of big headphones. So, bass articulation is definitely the word that comes out when we’re talking about the Stepdance (though keep in mind, the bass body is fairly thin).
The Stepdance that was used for this review comes with upgraded capacitors, and according to Sem who did the mod, the sound opened up and smoothens after the upgrade. However, I can’t help but noticing the treble to be a little rough when compared to the average amplifiers in this shootout. It boosts the apparent clarity, but at the expense of smoothness. But in a way, it’s quite a match to the overall dry sound of the Stepdance.
I ultimately think that the Meier is quite a specialized amplifier, similar to how the i-Qube was. It will appeal to people who values clarity and articulation very highly, and should be a good match to a headphone which is over warm and with plenty of uncontrolled bass. The i-Qube has a smoother sound and didn’t feel as dry in the mids and lows, but the Meier is better in bass impact and punch with a more natural timbre than the i-Qube. Either way, I think both amps remain pretty specialized solutions that I won’t recommend to the general crowd.