iBasso PB5 Review

Today, we review the iBasso PB5 Osprey, an overengineered portable NuTube Amplifier. It is selling for $1,499 USD.

Disclaimer: iBasso sent us the PB5 for this review. As always, I am here to share my honest experience with the product. We thank Paul from iBasso for the opportunity.

iBasso Audio

Founded in 2006 in Shenzhen, China, iBasso Audio has built a solid reputation as a flag bearer for portable audio around the world. With a focus on research and development, the company has been designing, developing, and manufacturing high-performance products tailored to the needs of audiophiles and music enthusiasts since its inception. Their portfolio includes digital audio players, DACs, amplifiers, headphones, and in-ear monitors. They continue to push the boundaries of portable audio technology every day.

What sets iBasso apart is their concentration on engineering excellence and their ability to incorporate the latest technologies into their designs. In addition, I personally believe that iBasso has had an incredible impact on the evolution and acceptance of personal audio around the world. You know how there are some companies in a certain industry that push the industry to be better? iBasso is one of those companies in my eyes.

Following the success of the D16 Taipan, a portable R2R DAC/AMP that redefines what is possible in its category, we now turn our attention to its sibling, the PB5 Osprey tube amp. Designed to complement the D16 both aesthetically and technically, the PB5 features NuTubes and a lot of magic under the hood. You can keep up with iBasso’s latest via their FB page.

If you want to catch up, you can check out the D16 review below.

iBasso PB5 Osprey NuTube Portable Amplifier

iBasso PB5 Osprey is an over-engineered, high-performance (trans)portable amplifier. iBasso has equipped the PB5 with an impressive selection of components: dual Nutube 6P1 vacuum tubes, 24-position analog stepped attenuator, six dedicated batteries for optimized power delivery, TI OPA827 op-amps, propriety film capacitors, Nichicon caps, BISS transistors, 1.7w@32Ω / 9vrms power output, the PB5 is a portable (or should I say transportable?) beast. Note that PB5 is a balanced-input-only amplifier.

Priced at $1,499 USD, the PB5 is positioned in the high-end segment of the portable amplifier market, targeting audiophiles who demand the best on the go. Sharing much of its DNA and design philosophy with iBasso’s D16 DAC/AMP, the PB5 is an ideal companion in aesthetics and performance synergy. We’ll take a look at how they work together and how the PB5 affects the SQ further in this review.

One of the key highlights of the PB5 is the integration of Nutube technology, which is a modern reinterpretation of the classic vacuum tube. But what exactly is Nutube, and why is it an intriguing addition to a device like this? Before that, here’s an overview of the specs below.

Specs & Highlights

• Dual Nutube 6P1 Vacuum Tubes
• x6 900mAh Batteries forming x3 8.4V battery-packs with complex PSU design
• TI OPA827 OP-amps, iBasso Film Caps, BISS transistors, HQ caps & more
• 24-Position 4-Section Stepped Attenuator Volume Control
• Charging Time: 2.5h | Battery Life: 10h – No PD. Only QC 1.5A or up.
• 4.4mm Input | 4.4mm & 3.5mm Output
• 1700mW@32Ω
• 9 Vrms Balanced Output | 4.5 Vrms Unbalanced Output
• Line-In Voltage: <2.5V
• Output Impedance: 0.25Ω
• 352g, 139x82x28mm
• Full specs are available here.
• Click here for iBasso’s wide network of distributors. 

Packaging & Accessories

The PB5 shares not only its design cues with the D16 but also its premium packaging and impressive presentation. The PB5 arrives in a sturdy cardboard box that protects its luxurious leather case during transport. Inside, you’ll find a leather case reminiscent of high-end watch boxes, with “iBasso Audio” embossed on the top and fine stitching along the rectangular edges. The aesthetic here literally screams premium. Upon opening this watch-style case, you’re greeted by a brown suede interior lining and another “iBasso Audio” lettering in black. The accessories and the unit itself are all neatly laid out right in front of you.

The PB5 is housed in a forest green leather drawstring pouch, ready to be revealed. The interior of the case is also lined with suede for a luxurious feel. This pouch serves as an excellent accessory to protect the PB5 from scratches during daily use. In addition, there’s another slim velvet/suede drawstring pouch that contains two 4.4mm interconnect cables and a USB-A to USB-C charging cable. One interconnect cable is about 15cm long, while the other is about 30cm long. Although the alloy used in the interconnects isn’t explicitly mentioned, I believe they’re made from a thinner variation of the monocrystal copper and SPC wires seen in the iBasso’s CB13 cable. They feature a braided design and are exceptionally flexible despite their 8-braid construction, which is a big plus. In addition, the connector part of the interconnects are rounded, CNC-machined metal shells, which look unique!

As with the D16, the PB5 comes with a quick start guide and warranty card, although the information provided is somewhat limited. What really stands out to me, as it did on the D16, is the forest green leather case. This velcro-fastened case has an aluminum plate opening on the back to help with cooling. While it adds a bit of thickness to the PB5, it is both aesthetically pleasing and functional, protecting the PB5’s aluminum chassis from external damage. It also eliminates the need to find and purchase a third-party case for this uniquely shaped device.

Design & Build Quality

The PB5 shares its core design language with the D16 but introduces several differences that distinguish it both functionally and aesthetically. The PB5 looks and feels like a premium piece of gear. The CNC-machined lineal grooves across the body create these beautiful light-and-shadow effects depending on how the light hits it. The aluminum body is subtle but classy, the kind of design that doesn’t scream for attention but still looks professional and unique. On the top panel, you’ve got iBasso’s motto, “In pursuit of perfection” in white under the model name. Normally, I roll my eyes at mottos like this, especially when newer companies come up with these, but after having known iBasso for over a decade, I’ll admit this one fits. They’ve earned it.

Starting with the back, you’ll notice a single USB-C port for charging. Unlike the majority of newer devices, the PB5 doesn’t support PD chargers or USB-C-to-USB-C cables, so you’ll need a QC-compatible USB-A charger brick that can do at least 1.5A. iBasso includes a USB-A to USB-C cable in the box, and you’re better off sticking with it to avoid headaches. Design-wise, the charging port and the two-switch array are inside these two small rectangular cutouts. The switches are simple but useful and provide tactile feedback while feeling solid. They’re two-step toggles, one for power and one for gain. The power switch lets you turn on or off the device, while the gain switch lets you choose between low/high gain. There are small red indicator markers that are located beneath the switches when set to OFF or LOW. It’s a nice touch that makes it easy to tell what’s what, like the older iPhone’s mute switch.

There are two hex screws on the back panel, and if you’re anything like me, they’ll immediately catch your eye. These hexagonal screws are all that stand between you and the PB5’s internals. Pop them off, slide the top aluminum cover, and you’ve got access to the magical guts of the machine, including the proprietary six-battery setup. Battery replacement is straightforward, but since it’s a custom system containing six batteries, you’ll most likely need to contact iBasso for replacements. They’ll walk you through the process, which is way more convenient than shipping the unit back. Honestly, I love that iBasso makes serviceability this easy. It shows they’re thinking about the long-term ownership experience, which is VERY rare in this price range.

Moving to the front, the PB5 greets you with its massive volume wheel. If you’re familiar with iBasso’s gear, you’ll recognize their signature 24-step analog attenuator, which we’ve seen on their flagship DAPs like the DX320Max and DACs like the D16 & DC-Elite. The wheel has a solid, satisfying feel, with clean, tactile steps, though the precise adjustment can be somewhat challenging for ultra-sensitive IEMs. That said, pairing the PB5 with the right DAC, such as the D16, lets you fine-tune the volume for those cases. We’ll talk more about DAC synergy; don’t worry.

Next to the volume wheel, you’ll find a 4.4mm balanced input alongside 4.4mm balanced and 3.5mm single-ended outputs. Having everything on one side is convenient for stacking and helps with the cable clutter, which is always a win in my book.

What really stands out, though, is the window on the glossy/glass top that gives you a peek at the Nutube circuitry. Those little vacuum modules glow with a neon green-turquoise hue that’s straight-up mesmerizing. There’s something about watching those tiny tubes light up that just feels good. It’s the same feeling I get with traditional vacuum tubes: warm, calming, and oddly satisfying. I spent way more time than I should have to try to capture the glow in photos, but it’s just one of those things that look even better in person.

Overall, the PB5 nails it in both design and build quality. Everything feels solid, well-thought-out, and functional without sacrificing aesthetics. The details like the red switch markers, the tube window, and the easy access to the internals show that iBasso knows its audience and cares about the experience. On that note, I’d like to talk a bit about iBasso’s attitude towards their customers in the next section.

The review continues on Page Two, after the click HERE or by using the jump below.

Page 1: iBasso, PB5 Osprey, Packaging & Accessories, Design & Build Quality

Page 2: The iBasso Way, Nutube Technology, Internal Details

Page 3: Sound Impressions, Match-Ups, Last Words