Here comes the new balanced amp from Ibasso! To counter RSA’s quad-mono SR-71b, Ibasso has created quite a monster portable amp in the form of the PB2. I’m sure you’ve all heard of it: 32 volts of swing and 2.5watts maximum output puts this portable in a desktop amplifier league.

IMPRESSIONS WITH FULL SIZE HEADPHONES
Of course the first thing I did when I received the PB-2 was to hook it to a Hifiman HE-6 to see if the rumors are true. Indeed it has enough power to drive the HE-6 to quite a good loudness level, and I’m only using the low-gain setting with volume control at 3pm!

While the PB-2 can never replace the impact and authority of a big desktop amp, the PB-2 can definitely take on a lot of entry level single ended desktop amps. For instance, listening to the HD650 in balanced, the PB-2 was able to grab a good control of the drivers, injecting a good dose of pace and making the HD650 feels lighter and more nimble than it normally is. I think in this sense the balanced drive really helps to pick up the pace of the HD650, as my Grace m902 ($1,500 headphone amp with single-ended headphone out) though having more impact and authority, doesn’t improve the pace of the HD650 as well as the Ibasso PB-2. Now that’s quite a compliment.

IMPRESSIONS WITH CUSTOM IEMS
With custom IEMs like the JH16Pro, the balanced drive gives an instant boost in soundstage size and bass quantity and you get a much bigger sound than you do when driving in single ended. However, I do think that while very impressive in short listening sessions, the balanced drive only increases the phase inaccuracy already inherent in the multi-driver IEM design. The balanced drive also didn’t improve things like articulation, detail extraction, imaging precision, or bass control out of the JH16, and again I will have to go with the Pico Slim or the RSA Shadow for my JH16.

OP-AMPS & BUFFERS
Opening the enclosure (Ibasso has supplied the hex key required to open the case), and I’m greeted with two rows of quad opamp arrays. It’s a pretty awesome sight to behold in a portable amp. The layout is very clean and symmetrical, as Ibasso had placed the messy part on the bottom side of the PCB. Ibasso also supplied an extra quad set of BUF634 buffers and an extra quad set of AD797 opamps, as well as dummy boards to bypass the buffer section. In total, you get 16 pieces of opamps/buffers along with the PB2.

Of course this is an incredible opportunity for opamp rolling. The PB-2 comes stock with the OPA604 op-amp and BUF634U buffer. The stock set up is actually quite good and has a very good tonal balance with good vocal presence, full mids and lows. Upon changing the opamp to the AD797, you get better bass control and more lively treble. When used in conjunction with the buffers, I felt that the midrange transition is not very linear when compared to using the OPA604 opamp. I prefer the AD797 without the buffer section, as it gives me the true AD797 sound.

My buddy Neob sent me a pair of dual-channel DIP OPA2111KP op-amps, which he said is a good pairing for the Ibasso P3, and indeed it is a very good opamp for the PB-2 too. The 2111 has a neutral presentation like the stock OPA604, but with a bigger soundstage and a more open sound. The treble is less agressive and also smoother than the OPA604, and so far it is the best match I’ve found for the PB-2. I haven’t quite tested the PB-2 with old time favorites like the OPA627, because I don’t have enough chips to fill in the quad-channel.

The buffer helps to add current to the output, which is useful for hard to drive headphones like the HE-6. But in terms of sound colorations, the buffer adds mid and low body, while lowering transparency. So, if I’m using the PB-2 with the 300 Ohm HD650, I’d rather have the buffer replaced by the dummy adapters as the amp runs cleaner without the buffers. Between the two buffers, the stock BUF634U is more neutral all around, while the DIP-package BUF634P WB (with the brown dale resistor soldered) is the same buffer running in high bandwith mode. The high bandwith BUF634 has 180MHz compared to 30MHz on the plain BUF634. For this reason, the BUF 634P WB is always the better choice for driving current hungry headphones like the HE-6, but keep in mind that battery life will also suffer tremendously (quiescent current averages 15mA vs 1.5mA on the low bandwith mode.)

As a recap, here is a general guide to the opamp and buffer configuration:

• OPA604 + BUF634U (stock configuration) – Neutral sound with good tonal balance.

If you want more treble, then go with the AD797 on the opamp section:

• AD797 + BUF634U – Better treble quality, drier on the mids to top compared to OPA604.

If you want more mids and low end body, change buffer to BUF634P WB (180MHz):

• Change buffer to BUF634P WB (180MHz) – Bigger sound, fuller bass and mids, shorter battery life.

If you want a more transparent sound and better texture on the bass areas, take out the buffer section and go with a dummy buffer.

• No buffer – Limited current, but still good for HD650, sound is cleaner and more transparent to the actual signature of the op-amp.

COMPARED TO THE PB1
Like the PB-1, the PB-2 has a very good build quality. I’m loving the new matt finishing from Ibasso, and I think it really looks good in silver. There are no sharp edges in the housing, finishing quality is very smooth, definitely Ibasso has improved their build quality a lot since the P2 days. I do have to say that the longer enclosure, though understandable given the power output, is a big turn off when I can be using much smaller amps like the Headstage Arrow or the Pico Slim. I think you’ve got to have a real need for the power output of the PB-2, otherwise it will make more sense to go with the other slim amp models. Another thing that’s preferable on the PB-1 is the placement of gain switch. On the PB-2, you need to open up the enclosure to get access to the gain jumpers, where on the PB-1 the gain switches are accessible through the bottom side of the amp.

Compared to the PB-1, the PB-2 has an almost identical sound signature and tonal balance. Ignoring the power output differences, the PB-2 on the stock op-amp and buffer sounds slightly warmer with less aggressive treble and more low end body, while the PB-1 has a better clarity on the treble area. When you take out the buffer and only run it on the stock OPA604 op-amps, then the PB-2 sounds improves the clarity on the treble to match the PB1 while still being warmer and more neutral.

(special thanks to Neob for the PB1 loaner).

END WORDS
Throughout my listening time with the PB-2, I almost never see the need to use the mid or high gain level, other than just testing how loud it can drive the HE-6 headphones. But for actual listening, I actually find the low gain to be enough even for the HD650 and the HE-6. With the HE-6, though the voltage swing is plenty, it didn’t quite have the authority to make a slamming bass impact. However, with the 300 ohm HD650, the experience is very enjoyable as the PB-2 is perhaps the most affordable amp I’ve tried with the HD650.

Set up used for review:
Headphones: Hifiman HE-6, Sennheiser HD650, JH16Pro
Source: Hifiman HM-602, HM-601, Ipod Classic
Amplifiers: Ibasso PB-1, Ibasso PB-2, HeadAmp Pico Slim