iBasso PB5

Whisper it quietly, indeed. PB5 works near-silently because iBasso's stepped resistor analog volume control shows up where it could be most crucial – in their first battery-powered tube and solid-state hybrid amplifier.

Said stepped attenuator preserves the resolution of your best DAP sources in the presence of Nutubes that may not otherwise share the same noise performance as the rest of PB5's carefully assembled transistor circuit. 

Before that begins to sound like a problem, the gains from inserting Nutubes into PB5's (read: mini DX320 Max TI's) signal path far outweigh any cons. Beyond granting the kind of natural, spacious and effortless sonics tubes are known for, Korg's fluorescent 6P1 dual triodes pay dividends on the circuit design front too.

READ ALSO The benefits of adding input tubes to a circuit

As triodes, Korg's 6P1s provide iBasso access to an all-important square law transfer function for wide operating conditions.

With tubes – audio's long-established ideal input device – now working differentially in balanced push-pull configuration to receive signal from your 4.4mm source, iBasso's proprietary stepped resistor attenuator takes charge of volume.

Additionally counting on common-mode rejection, it's this proprietary volume control that enables PB5 to play it delicately into your flagship earphones for enjoyment at realistically lower volume levels.

Because, it's easy to play it loud, but everyone knows it's in playing back tiny sounds that is the litmus test of a hybrid tube/solid-state amp capable of outputting as much SPL as PB5.

Transparent at any volume setting down low as much as up high, with virtually perfect +/-0.1dB channel-matching, this iBasso tubed behemoth exposes detail buried deep around the noise floor of your music.

So begins the rest PB5's fully-balanced, true differential solid-state circuit whose push-pull operation produces odd harmonic distortion that dovetails perfectly with the naturalness of its Nutubes.

Built with individual transistors of iBasso's choosing allows great control over PB5's tuning, while an immense operating voltage over 16 volts grants an innately linear open-loop circuit, with substantially less negative feedback, to be fashioned.

At the tip of PB5's spear are buffers capable of outputting more amperes of current than is needed in reality, while keeping output impedance near zero. Said power stage is another call for iBasso's Super Class A to appear. 

Current mirrors ensure PB5's push-pull operation works without crossover distortion, yielding Class A-like performance at all power output levels. That makes for extremely linear open-loop operation before negative feedback is applied ... yet mostly avoids the heat and inefficiency typically associated with Class A designs.

With superb damping factor as a voltage source, enough standing bias current and signal-to-noise performance to follow today's flagship IEM impedance down low, you still know PB5 will be even more in its element pushing TOTL headphones.

That's especially when you consider its six separate batteries providing clean, independent power to each critical section of PB5's circuit. 

Everything from Focal to a Fostex and Rosson Audio Designs plus Yamaha and ZMF Headphones is applicable. Flexibility is the operative word here and sources like Cayin Audio's N7, iBasso's own DX260 plus HiBy Music's RS6, R8II and RS8 will be queuing up to lend their signal to PB5.

PB5 is the perfect segway to add tubes to your portable flagship sources, but it's so much more. Through Osprey's stepped attenuator volume control and Super Class A output stage, DX320 Max TI's spirit lives on.

Check out the rest of iBasso's sources for PB5 here, or view our other DAC/amps here.