Synergy
IEM Pairings
The PB5 Osprey output impedance is 0.25Ω or less, with minimal background noise, making it an excellent choice for those using sensitive IEMs and concerned about background hiss.
While not entirely hiss-free, it performs much better than competing dual-tube amplifiers like the C9 and significantly outshines older models such as the Phatlab Chimera.
With IEMs like the VE10, I noticed a slight microphonics or tube ping moment upon initial cable insertion. However, this dissipates quickly, allowing you to focus on listening.
Paired with the D16 Taipan, channel balancing from the stepped potentiometer is excellent at low volumes, even with sensitive gear.
For tonal preferences, I tested five IEMs using the D16/DX320 MAX Ti via USB and a line-out to the PB5: the Noble Audio Onyx, Campfire Audio Andromeda 2020, Vision Ears VE10, THIEAUDIO Monarch MKIII, and Empire Ears ESR MKII.
All five performed exceptionally well in dynamic range, with the only caveat being a brief tube ping on the initial connection.
I preferred IEMs with more treble sparkle or neutral tuning, like the Monarch MKIII and ESR MKII. The ESR MKII excelled in midrange clarity and staging width, while the Monarch MKIII’s treble was notably smooth and clear, surpassing what I’ve experienced with other portable amps.
I’d also include the VE10, despite its non-neutral tuning, due to the snappy performance of its dynamic driver. Among the five, its low-end performance offered the best definition and layering.
However, I’d shy away from warmer IEMs with limited treble presence, like the Onyx and Andromeda 2020. While they didn’t sound bad, the PB5 doesn’t add sparkle, making it less ideal for such pairings.
Headphone Pairings
For headphone pairings, I tested the HEDDphone Two, the Audeze LCD-XC 2021, and the Caldera Open and BOKEH from ZMF Headphones. The common theme throughout was dynamics on the low end and warmth through the mids and highs.
If you are using a DX320 MAX Ti on its own you will get a cleaner sound with more treble sparkle but the low-end will sound comparatively neutral with less body. The PB5 Osprey resolves that and then some, particularly so with the Caldera and Bokeh.
Though the Bokeh does not necessarily need that much power to sound good you will notice just how much heavier the low-end sounds in comparison to running it through a DAP only.
The Caldera has a similar response using the DX320 MAX Ti, sounding clean and clear with more treble sparkle and a slightly leaner midrange timbre. The PB5 Osprey thickens everything up, delivering more weight on the lows and a more saturated set of mids.
The flip side is the mids and highs with a slight softening compared to cleaner sources. The HEDDphone Two and the LCD-XC had some pros and cons to this.
Both sound dynamic and powerful with the PB5 and in the case of the LCD-XC 2021, I much preferred its smoother treble response to pairing directly from the DX320 MAX Ti.
However, the HEDDphone Two sounded just a little too soft on the upper-mids and highs at times. You can mask that with bass-heavy recordings, but if you are after a clean and clear tone going with a more neutral source might be preferable.
Select Comparisons
The following comparisons to the iBasso PB5 Osprey were completed using the iBasso D16 Taipan and DX320 MAX Ti as source and decoder with a mix of the Vision Ears VE10 and the HEDD Audio HEDDphone Two for matching headgear.
Cayin C9
Note we will be also comparing the PB5 Osprey to the C9ii when arrives shortly in our office here for review.
Technical Specifications
Like the PB5 Osprey, the Cayin C9 is a balanced engineered dual Nutube 6P1 tube portable headphone amplifier with a multi-battery power supply. Both amplifiers have their tube system supported by a spring-loaded suspension system.
The C9’s maximum output power is weighted by Cayin at a maximum of 2.6W into a 32Ω load when going balanced which is a bit higher than the 1.7W capability of the PB5 Osprey.
The C9 drops to 700mW on its single-ended output, however, iBasso has not listed the weighted 32Ω rating for the PB5 output, instead giving a maximum output voltage of 4.5Vmrs. I would have to presume if the balanced output is 1.7W then the SE is lower than 700mW on a 32Ω load.
Both have high and low gain features with a line-level input with a balanced 4.4mm input. However, the PB5 lacks the C9’s 3.5mm LO option as well as Pre-out functionality. That may well be one factor in the additional $500 on the C9’s price.
The C9’s technical calling card is its dual mode and dual timbre operability allowing you to switch between the tubes and a solid-state topology as well as a tube timbre and a solid-state timbre giving you up to 4 different performances from a single amplifier.
The PB5 Osprey stays resolutely in a tube mode with its unique stepped attenuator though both have a Class A (Super Class A for the PB5) amplifier topology to call upon.
One useful insight for the C9 that you will only notice after years of use is its four replaceable 18650 lithium batteries which ‘trickle drain’ and die even when turned off. I have yet to experience that with the PB5 battery pack.
Design
Of the two, the C9 feels more substantial in my hand, and the one I would more likely term as transportable. Its engineering is on a higher level in terms of chassis finishing and its longer narrower body feels right on the desk.
However, the PB5 Osprey would be the unit I would more likely move around with, especially with the included leather case and lighter weight. In a strange way, it feels more robust and manageable for single-handed use. It might well be a case of elegance versus toughness.
Both amplifiers have the majority of their I/O on the front panel with the PB5 moving gain controls to the rear along with power, USB-charging, and its battery charging status LED.
The C9 keeps its charging battery status and USB-C charging socket to the rear as well though its multi-stage charging status indicator is more useful. Its power button to the front and white labeling all around is almost more legible, at least to my older eyes.
Since the C9 could be considered more feature-rich, it does have a lot more operability on the front panel including the SE/Balanced Line inputs and the multiple operational and timbre modes. It makes for a busy-looking but well-organized façade.
The PB5 Osprey is cleaner on the front panel, it lacks the array of options of the C9 but its stepped attenuator is arguably a strong centerpiece attraction on the front panel.
One final design note. I prefer the PB5 tube glow panel design over the thin slots of the C9. I prefer to see a lot of that green low over the slither of light from the C9.
Performance
Paired with the DX320 MAX Ti and the D16 and using the Vision Ears VE10, a sensitive IEM, you can hear a higher level of background hiss from the C9’s low-gain 4.4mm balanced output, a level that is less prevalent when paired with the PB5.
On the flip side, the PB5 Osprey’s tube suspension system has less tolerance, meaning it is more susceptible to tube microphonics.
Tonally, I find the PB5 Osprey to deliver a more ‘driven’ impactful and ‘fleshy’ sound compared to what I would define as the C9’s more classic spin on tube sound, the atmospheric or more ambient presentation with a slightly relaxed sweeter tone.
Staging-wise, the C9 sounds a little taller and purer on the highs, but not as forceful in the mids and not as punchy in the mid-bass. Both deliver an excellent sub-bass response from the VE10 but I hear the PB5 Osprey mid-bass reaching just a little higher which is a strong factor in that ‘driven’ impression.
The PB5’s comparatively tapered highs mean the soundstage is more bass to mids in terms of grabbing your attention. This is fine by me, the VE10 is built to deliver beautiful vocal performances so the stronger fundamental and thicker midrange tone from the PB5 suits it.
However, if you need a bit more space, a bit more height and air then the C9 can deliver a more open or spacious-sounding experience.
For timbral choices, you can get close to the ‘urgency’ of the PB5 by selecting the Class AB mode on the C9 combined with the tube timbre. Class A slightly softens the mid-bass punch and solid-state is too dry for my tastes.
Phatlab Chimera
Technical Specifications
The Phatlab Chimera is also dual tube portable headphone amplifier but it has a slightly different topology to the PB5.
The Chimera circuit is based around a switchable dual-mode JFET or transistor-based design combined with a triode or tube-based alternative output. That means that like the C9, you can operate in either a solid-state or tube mode on the Chimera.
Its tube mode does not use Nutube technology but rather a dual Jan 6418 subminiature tube configuration which is more prone to microphonics or ping than the suspended configuration of the PB5.
The PB5 does seem to have a bit more clout to its amplification regardless of mode capability from the Chimera at 1.7W compared to 1W on a 32Ω load. And though both only have a single line-level input, the PB5 offered a balanced 4.4mm rather than the Chimera’s 3.5mm line input.
The Chimera is not a ‘true balanced’ amplification topology but there is a substantial boost in output voltage for the 4.4mm balanced output. So also in its low/high gain 14dB swing or roughly 4.5 dB more than the PB5’s gain setup.
DC-In is 5V, similar to the PB5 but the Chimera’s older design still uses a micro-USB connection and not the more modern USB-C option. A slight inconvenience and I say slight because both will not accept PD2.0 charging with each running about 10 hours battery life cycle and 2-3 hours charging time.
Design
For an older product, the Chimera shares a similar design language to some aspects of the newer PB5 Osprey housing.
Both are black aluminum shells and both have ribbed cornering though the rounded side panels of the Chimera make it more comfortable to hold in the hand.
The PB5 is narrower and a little heavier than the Chimera and surprisingly I would call that additional weight a slight advantage for interconnects and large headphone jacks. I suspect if were not for the Chimera’s soft feet on its base panel it might move around a lot more.
One clear design advantage of the Chimera is the socket legibility. The white labeling makes it so much easier to read than the teched low-profile alternative on the PB5.
The spacing on the Chimera panels for the sockets is also quite similar to the PB5 with large rounded recessed enclosures and yes, the fat barrels of the PB5 interconnects fit beautifully on the 4.4mm ports. The USB and mode stage operability on the rear of the Chimera is also easy to access.
However, getting them out can be a challenge as the Chimera is finished with protruding sideguards which blocks access to the left side of the barrels making them very hard to take out.
And yes, you get a nice tube glow out of a top panel on the Chimera. However, this one is a classic orange light rather than the NuTube green.
Performance
I kept the same setup as the C9 comparison meaning the DX320 MAX Ti with a USB output to the D16 Taipan and a lineout to the Chimera with headgear connected to its 4.4mm output in a low gain tube mode.
If you are using a Chimera I suggest the PB5 Osprey as your portable tube amplifier upgrade. The performance difference is not subtle, especially if you are using sensitive IEMs like the VE10.
The main culprit is the noise floor and tube microphonics level on the Chimera in tube mode. The older dual tube design does not offer the same suspended protection as the PB5 meaning any taps or cable connects result in a loud and long ping, which is elevated the more sensitive the IEM is.
Throw in a higher background hiss level on the balanced output and you start to hear some diminished dynamic range, poor channel and instrumental separation, and a less complex or deep-sounding soundstage from the Chimera.
The PB5 delivers a blacker background and a more refined tonal quality to its performance making it much more suitable for modern IEMs. Clarity leaps upwards, especially on the periphery or on the lows with passages that have more complex bass layering.
The Chimera is punchy with a similar ‘driven’ characteristic as the PB5. Though not quite as saturated or as fleshy in its midrange timbre the energy from its mid-bass punch gives it a livelier character compared to the chilled C9 tube timbre and Class A mode.
My Verdict
The iBasso PB5 Osprey is a beautifully smooth, weighty, and fulsome-sounding portable tube amplifier.
It has plenty of power to drive demanding headphones such as the Caldera or the HEDDphone Two and can deftly handle IEMs with ease at the same time. It’s probably my favorite portable amplifier I have had the pleasure to review in a while.
This is a mature analog-tuned offering, mating perfectly with the D16 1BIT DAC. Combined with the DX320 MAX Ti, I would consider this iBasso’s unofficial high-end desktop stack.
Where can it improve? Hard to say. Some might prefer a non-stepped attenuator if they are not pairing it with the D16 Taipans granular DAC volume-controlled output. Others might hope for a more modern housing similar to the C9 and a few might also hope that a new iteration might add a standard 3.5mm LO alongside.
Personally, I think the PB5 Osprey is niche enough to appeal more to hardcore users thus avoiding the pressure of having to develop more features for the masses.
If you are heavily invested in the iBasso ecosystem I would call this the missing link for demanding headphone users. It sounds nothing like the vast majority of the company’s more neutrally-tuned gear, which is an excellent highlight in its own right.
iBasso PB5 Osprey Technical Specifications
- Output Voltage: 9Vrms (4.4mm BAL) | 4.5Vmrs (3.5mm SE)
- Output Power：1700mW+1700mW @ 32Ω
- Output Impedance: 0.25Ω (4.4mm BAL) | 0Ω (3.5mm SE)
- Frequency Response 20Hz-40kHz +0.5 dB/-2dB
- Recommended Headphone Impedance: 8~600Ω
- Input Port: 4.4mm TRRRS BAL
- Output Port: 4.4mm TRRRS BAL | 3.5mm TRRS SE
- Gain: +11.5 dB (High Gain) | +2 dB (Low Gain)
- Size: 5.4″ x 3.2″ x 1.1″ (139mm x 82mm x 28mm)
- Weight: 352g
