PORTABLE BALANCED AMPS
RSA SR-71B ($650), RSA PROTECTOR ($475), IBASSO PB-1 ($229), and the IBASSO PB-2 ($325)
The easiest differentiation between the two brands offering portable balanced amplifiers, again, is the sound signature. The RSA Protector and the RSA SR-71B are both members of the RSA house sound: warm, dark, and a thick bottom end. When Peter heard both the PB-2 and the SR-71B at my place, he vastly preferred the SR-71B because he’s been a big fan of the RSA sound. The Ibasso balanced amps contrasts the RSA balanced amps with a livelier presentation, more alive treble down to the upper mids, but not as full on the low mids and bass regions. To Sem, the RSA balanced amps are too dark for his taste, and lucky for his wallet, he strikes a match with the Ibasso better.
If you have always been a fan of the RSA sound, then it’s clear that you should go for either the Protector or the SR-71B. Between the two, the SR-71B with its quad mono topology not only offer improved power output from the Protector, but also greater level of separation and soundstage size. Even when you’re not using a big, heavy to drive full size headphone, the improvements on the SR-71B’s sound quality is quite obvious over the Protector. The only factor you need to consider is if your chief financial officer allows the budget for the SR-71B.
Going balanced will give you the benefits of a wider soundstage, a boost in the lows, and overall a more exciting sound than in single ended. The word “steroids” seem to be almost fitting to describe the changes. Think Hulk, and you get a rough idea of the balanced output RSA amps with the single ended RSA amps.
If you’ve feel that you prefer an amp with a livelier treble, or you have tried an RSA amplifier previously and thought it to be too dark, then the Ibasso is the way to go. In the case of the Ibasso PB-1 and PB-2, the PB-2 takes a small step back in terms of refinement and resolution, though improving tremendously in power output. If you’re using the amps to drive a typical dynamic headphone, like the Sennheiser HD650 and HD800, then the PB-1 already come with plenty of voltage swing to drive the 300 Ohm headphones to really loud levels, especially in balanced drive setting. I don’t remember if I have tested the PB-1 with the 600 Ohms Beyerdynamic T1 or DT880, but seeing the available headroom the PB-1 has for driving the HD800, I think it should be able to drive the T1 and the DT880-600 just fine.
The PB-2 becomes interesting if you consider rolling op-amps to get a superior sound output, or if you consider using a beefier output buffer section like the high-bandwith BUF634 that Ibasso shipped with the PB-2 package. The PB-2 currently holds the trophy for the most powerful portable headphone amplifier, as it is able to drive the Hifiman HE-6 Orthodynamic headphone to good levels without breaking up. This is done with the high bandwith BUF634 that is shipped with the PB-2. The PB-1 can’t output this kind of power, and so you’ll need to get the PB-2 for the Hifiman headphones. To Lisa 3 and RSA SR-71A owners: yes, the PB-2 is more powerful than your current amplifier.
Some people ask me how the amps would sound if they are only using the single ended section, perhaps because they haven’t got the proper balanced cable for every single headphones in their possession.
If you’re in the Ray Samuels camp, then I can say that you’ll be better off with the single ended amplifiers, either the SR-71A, the Mustang, or the Shadow depending on your needs. Those three amps will give you a better sound quality in single ended than you will get with the SR-71B or the Protector in single ended. If you’re in the Ibasso camp. Then I would gladly steer you toward the P4 Warbler, as it will give you a better sound in single ended than you get on the PB-1 and the PB-2.
Having explained what I feel to be the core difference between the RSA and the Ibasso stuff, I would like to take a step back and talk a little bit about balanced amplification.
NOTE: This section is a sidestep from the review and is a bit technical. Feel free to skip it and move to the next page if you are not interested.
Balanced amplification was initially a feature seen on the flagship $2,000+ desktop amplifiers. It makes sense to have them priced as a flagship, since a fully balanced amplifier require twice the amount of circuitry of single ended (or unbalanced) amplifiers. Not to add the additional requirements such as the dual mono power supplies (though not a must, but often goes together) and dual transformers, quad-stack potentiometers, additional input and output paths, bigger chassis requirement, heat management, and so on. So, if a single ended amplifier costs $1,000 to make, then the same amplifier in balanced configuration would at least double that cost into the $2,000 region. The long associations of balanced topology with flagship models somewhat correlates to the “ultimate set-up” stigma surrounding a balanced amp, while it is not always the case.
What happens in a balanced topology is that you have two amplifiers driving one side of your headphone, and another two driving the other side of your headphone for a total of four amplifiers working simultaneously to drive one headphone. On a conventional unbalanced topology, you only have one amp driving one side for a total of two amplifiers working simultaneously to drive one headphone. Because two is better than one, then four is certainly better than two? At least that’s what you often hear — and it does make sense to a certain degree. When you have two amplifiers driving one side of your headphone (aka two amplifiers driving one driver), you get double the slew rate, which will improve the amp’s square wave response and make it more accurate to the input signal. Feeding a fully balanced signal also helps to raise the effective gain, giving you double the amplitude of the same signal, unbalanced. So, with a fully balanced system, you get twice the voltage swing, and twice the slew rate as the same system running in single ended. Power output will increase due to the increase in voltage, but due to heat and current output constraints, probably slightly less than double the single ended output. Good stuff, but amplifiers are not merely about voltage swing, slew rate, and power outputs.
If I talk to people in the high end audio circle, surprisingly very few of them are even aware of the unbalanced vs fully balanced debate. They would go into lengths debating the merits of branded power cables and even branded IEC connectors, but, interestingly, for them balanced or unbalanced is just something that a pre-amp manufacturer may choose to include for compatibility with studio gears. Now, it happens that every headphone enthusiasts that roams the internet knows the benefit of balanced drive. My brother in law happens to be in favor of a balanced system for his 2-ch set up which consists of a Mark Levinson No.32 preamp, some Krell monoblocks and a pair of Magnepans. But even then, the Krell monoblocks doesn’t output a differential signal to the Speakers (the Magnepans’ transformers are what created the differential signal to the ribbons). Are speaker guys really that ignorant?
As with everything in life, you have to look at both sides of the coin. The transistor vs vacuum tube debate. The discrete vs chip debate. The single vs multi drivers debate. The push-pull vs single-ended debate. The OT vs OTL debate. The Planar vs Dynamic debate. Sennheiser vs AKG debate (just kidding). And this time, unbalanced vs fully balanced debate.
So, what’s the downside with balanced amps? I’ve played around with a few balanced amps, both big and small, also the four portables being discussed. What I witness is that although the soundstage widens, the imaging accuracy and center image in general, suffer. Several factors come into play here. First and foremost is the issue of component matching. Very critical in obtaining a perfect symmetry between the right and left channel, which would in turn affects the soundstage image. Matching for pairs is not that difficult, but matching for quads are far more difficult. I am building an electrostatic amplifier at the moment, and I’ve yet to come up with a decent paired quad after going through 40 pieces of transistors ordered from the same vendor (and likely close in manufacturing batch). The Beta22 amplifier comes with 30+ transistors in one channel, and at four channel, that means matching 120+ transistors, not to mention the diodes and the resistors. Now, if you’re talking about a medium-large quantity production such as these amplifiers, how tight of a tolerance can you afford to implement on the assembly line? The effect of component asymmetry can be quite profound when you’re listening critically through headphones.
The second factor is space constraints. Although I am not familiar with the circuit design used in these amps, it’s common sense that it’s easier to build a good amplifier if you have a big enclosure to design a circuit around. There are exceptions of course, like the 47Labs Gaincard, but most high quality amplifiers come in really large enclosures. The third factor may sound insignificant, but also just as important: volume control. As of now, all these balanced portable amps are limited to the lower resolution analog potentiometer options, whereas the unbalanced amplifiers come with fancy digital volume controls and stepped attenuators. Analog potentiometers are very critical to the input signal, and this puts the balanced amplifier in a strong disadvantage against single ended amplifiers that come with sophisticated volume controls.
One of the reason that desktop balanced amps sound so good is that they have all the space they need to double the size of the amplifier circuitry without having to cut corners. High quality balanced volume controls are also plenty. And given the premium price the desktop balanced amps command, they can afford to be critical in their component matching. With the portables, however, there are a lot of constraints with a portable balanced amp, and so the result has been quite mixed. Some people love them, some people hate them. Some people love the wider and bigger soundstage that they get, some people hate the inaccurate imaging and the lack of a proper center image. Some people love the bass response, some people prefer a more articulate and the better texture of the single ended amps.
I think it boils down to each individuals, and what they are looking for in an amplifier. But the bottom line is quite simple: The balanced amps here give you more power output, wider soundstage, and more bass quantity. The single ended amps here will give you better soundstage imaging, some of them have better resolution levels, and better articulation.