iBasso PB5 Review

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The iBasso Way

iBasso has consistently demonstrated consumer-friendly practices that set them apart in the audio industry. This philosophy dates back to their early products, such as the DX90 DAP, which supported user-replaceable Samsung S3 batteries. iBasso continues the production of batteries for devices as old as the 12-year-old DX100, ensuring that products don’t become obsolete due to battery failure. The D16 and PB5 continue this tradition with easy internal access via two hex screws and a simple battery replacement process that requires only sliding off the top cover.

Nutube Technology

This is where things get really interesting. The PB5 is built around dual Korg Nutube 6P1 vacuum tubes, which are essentially a modern reimagining of traditional triode vacuum tubes.

Noritake Itron and Korg are the creative forces behind the Nutube 6P1, blending expertise from two unique industries. Noritake Itron, a subsidiary of Noritake Co., has been a pioneer in vacuum fluorescent display technology since the 1960s, with a long history of engineering precision.

On the other hand, Korg is a renowned musical instrument manufacturer with decades of innovation, crafting iconic synthesizers and various audio solutions. Together, they reimagined the traditional vacuum tube, using Noritake’s advanced display technology and Korg’s audio expertise to create a modern, compact, and power-efficient vacuum tube for the next generation of audio devices.

Unlike conventional vacuum tubes that are bulky, power-hungry, and somewhat fragile, the Nutube aims to solve all those issues. It is tiny, occupying less than 30 percent of the size of a regular vacuum tube, and runs on a low voltage of just 5V, making it perfect for portable, battery-powered devices like the PB5. And while it is small, it still retains the core magic of vacuum tubes: rich harmonic overtones and a natural, organic sound.

If you are wondering how this is possible, it all comes down to its design. The Nutube uses the same anode-grid-filament structure found in traditional tubes, but thanks to Noritake’s expertise in vacuum fluorescent display technology, it consumes just a fraction of the power while delivering up to 30,000 hours of continuous use. This means you get the warmth and musicality of tubes without worrying about replacements or overheating.

But here is the question: what does this actually do for the sound? In a nutshell, the Nutube gives the PB5 a uniquely analog sound. We know from the D16 that iBasso has been aiming for that natural analog sound signature with this twin (D16 & PB5) release, and the PB5 is for those who already have a DAC or want tube magic on top of the D16’s R2R architecture. It adds a sense of naturalness and realism to instruments and vocals, creating a more organic, musical presentation that is usually hard to achieve with solid-state circuits. Before we go in-depth, you should know some essential technical aspects of the PB5.

Internal Details

The PB5 is a meticulously engineered device built with top-tier components designed to extract every ounce of performance possible. Let’s start with tubes. To counteract the microphonic nature of Nutube vacuum tubes, iBasso implemented a two-step suspension mechanism. This design uses physical isolators to minimize vibrations and external interference. The cathode input further reduces impedance, ensuring that signal clarity remains unaffected.

iBasso uses Texas Instruments OPA827 operational amplifiers, chosen for their warmer, bolder tonality. Beyond the Nutubes and op-amps, the PB5 incorporates high-quality capacitors from renowned brands like Nichicon and Siemens, along with BISS transistors for reliable current delivery. The PB5 also features iBasso’s proprietary aluminum foil audio capacitors, which are also used in the flagship DAP DX320’s AMP11 MK2S amplifier module.

One of the standout features of the PB5 is its six-battery configuration. Instead of opting for a simpler single-battery setup, iBasso designed the PB5 with separate power supplies for different sections of the circuitry. Two batteries exclusively power the Nutube circuitry, while the remaining four are allocated to the amplifier modules. Based on the configuration of three 8.4V battery packs, it’s somewhat reasonable to assume that the setup might follow a 2x2x2 distribution: two batteries for the Nutubes, two for the left channel amplifier, and two for the right channel amplifier. This separation would mean that each channel operates independently, minimizing crosstalk and interference while maintaining superior channel separation. However, this is only my guess.

Another plausible configuration could involve four batteries working in parallel to power both the left and right amplifier channels. This arrangement would lower the impedance of the power supply, which is critical for maintaining stable current delivery. Lower impedance reduces stress on the batteries and allows for more efficient power delivery, minimizing voltage sag.

Either way, this electrical isolation is critical in preventing cross-contamination between power domains, which can introduce noise or degrade the signal. In audio, stable power delivery is non-negotiable. Any fluctuations or interference can affect sound quality, leading to distortion or loss of detail. iBasso addresses this with its filtering and power regulation mechanisms, guaranteeing that each component receives clean, stable power.

Also note that the PB5 also runs entirely on battery power, even when plugged in. When the batteries are fully charged, the charging circuit disengages and the PB5 continues to operate on battery power. Once any of the battery packs’ voltage drops below 8V, the charger reactivates to top them off.

The volume control on the PB5 is another example of iBasso’s no-compromise SQ approach. Unlike digital volume controls, which can degrade signal quality due to bit truncation, the PB5 uses an analog stepped attenuator. This 24-position, 4-section design offers precise channel balance with a tolerance of less than ±0.1 dB. While the steps might feel large for IEM users, pairing it with a compatible DAC like the D16 allows for fine-tuning. Analog volume control isn’t just about accuracy; it’s about preserving the integrity of the audio signal as it passes through the device.

To me, it’s clear that iBasso didn’t just throw high-end parts together. I genuinely believe they meticulously designed every aspect of this amplifier to meet the expectations of their fanbase, which, I should mention, is among the most veteran/knowledgeable in the audio community.

The review continues on Page Three, 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