FX-Audio Tube 02 Pro Review

FX Audio Tube 02 Pro review featured

Today, I’m reviewing the FX-Audio Tube 02 Pro tube headphone amplifier and preamp. The Tube 02 Pro features dual JAN 5725W tubes, dual Aux inputs and a budget-friendly price. The cost is $80.

Disclaimer: This sample was provided by the Hi-Fi College store for an honest review. All observations and opinions here are based on my experience with the product.

FX-Audio Tube 02 Pro Review
The FX Audio Tube 02 Pro has a warm yet clean sound and offers room for tube customization, but may not be ideal for sensitive IEMs.
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Good end to end extension
Clean, transparent sound
Solid build quality
3.5mm and 6.35mm headphone outputs
Great overall value
Not the best match for sensitive IEMs
Our Score

FX-Audio Tube 02 Pro Review

Tube 02 Pro design


The FX Audio Tube 02 Pro boasts an aluminium chassis with a brushed matte black finish, exuding a sleek and refined aesthetic. Although the overall build quality feels solid and the unit looks impressive when powered on, the garish branding and product description printed on the front panel detract from its visual appeal.

The front panel features two buttons: a multi-function button that powers the unit on or off with a long press, and cycles between the two AUX inputs with a short press, and another button that toggles between low gain and high gain. While the high gain setting only boosts the output by +2.5dB, some users may still find it useful.

In the middle of the front panel, there are 3.5mm and 6.35mm single-ended outputs, and on the right side is a smooth-turning volume knob that allows for fine control of the audio output. The volume control is analogue, so there may be some channel imbalance, particularly when using sensitive IEMs at low volume levels.

The back panel boasts a minimalist layout, featuring two single-ended auxiliary inputs, a single auxiliary output, and a 12V power input. The Tube 02 Pro automatically sends the audio signal to the auxiliary output by default, while the RCA output automatically disconnects as soon as you plug in headphones to prevent any potential damage to your headphones or hearing.

FX Audio Tube 02 Pro I/O rear panel

Tubes and Power Output

Moving on to the tubes, the 2 JAN 5725W tubes sticking out of the top of the unit are the main attraction. Acting as a buffer stage to the transistor amplification circuit, they provide the best of both worlds: a warm tube sound with the power and stability of solid-state amplification.

For those who enjoy tube rolling, these tubes can be replaced with 6j1 and 6j2 tubes, and some other types have also been reported to work. This opens up the possibility of experimenting with different tube sounds.

The tubes emit a warm orange glow that matches the colour of the LEDs on the front panel. However, don’t be fooled by their instant brightness when you power on the unit. They are actually lit up by LEDs placed underneath them. The real tubes take some time to warm up and reach their optimal performance. The good thing is that they don’t get too hot, and neither does the rest of the device.

The headphone section provides an output power of 850mW @ 32Ω, which should be suitable for many headphones, including the Sennheiser HD650. In fact, even in low gain, I rarely push the volume dial above the 9 o’clock position with my HD650s. The line output level of the Tube 02 Pro is 1.7rms, which is a typical level for this type of device.

FX Audio Tube 02 Pro chassis


I tested the Tube 02 Pro with the excellent SMSL DO300 DAC and fed it a series of Hi-Res FLAC files. I noticed some hum with sensitive IEMs, but not with full-size headphones. The noise was not loud enough to bother me, but if you mainly use acute IEMs, this might not be the best addition to your setup.

The Tube 02 Pro has a clean and surprisingly vigorous sound signature. It doesn’t have the grace or smoothness of the Feliks Audio Elise (not that I’d expect it to) but it sounds more composed and articulate than I was anticipating considering its price.

I was impressed with the sub-bass extension on this little device; it performs almost as well as similarly priced solid-state amps. There’s a tiny bit of roll-off in the lowest of the lows but you’ll need some good headphones or IEMs to even be able to notice. Mid-bass notes sound full and weighty, which I enjoyed, particularly with jazz and string instruments.

So the depth is there but how does it perform in the midrange? The mids have a nice clean tonality with a smidgen of added richness. However, the sound is transparent, detailed and dynamic.

The Tube 02 Pro’s treble extension is top-notch with no perceived signal loss. The highs sound airy yet slightly softened. The treble is sweet and extended, with no trace of grain or harshness.

Tube 02 Pro rear panel angled


Overall, I think the FX Audio Tube 02 Pro is a great amplifier for anyone who wants to enjoy a tube sound without sacrificing power or stability. It’s well-built, easy to use, and offers some room for customization with different tube types. The only downside is that it doesn’t have a USB input or a DAC function, so you’ll need a separate source for your digital audio files.

In addition, this device may not be suitable if you primarily use sensitive IEMs because of potential channel imbalance and background noise. However, I can heartily recommend it for headphones and active speakers.

Tube 02 Pro specifications

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9 months ago

I have been using the Tube-02 Pro for over a year. The first thing which I did after using it for a couple of days was to perform some checks on how the tube sockets are wired. Since the socket pins 5 and 6 are connected, and since the socket 2 and 7 are connected, this means that any EF95 tube can be used with the TUBE-02 amplifier. This also means that the 5725 tube’s sharp cutoff feature (which is useful for specific non-audio applications) is completely disabled such that the 5725 tube is forced to behave exactly like a 5654 tube. I have been using GE JAN5654W tubes in this headphone preamp for nearly a year. I initially swapped the supplied GE JAN5725W tubes with Voskhod Rocket 6ZH1P-EV tubes. I liked the sound of the Voskhod tubes very slightly better, yet these tubes had a faint humming sound which would get louder if I held my fingers near these tubes. I swapped out the Voskhod tubes with a matched pair of GE JAN5654W tubes. As mentioned, the 5654 tubes sound exactly like the 5654 tubes. I don’t have any faint humming issues with either of the GE tubes. I have been using a matched pair of the 5654 tubes in the Tube-02 Pro for nearly a year. The GE 5654 tubes are far more readily available in comparison to the GE 5725 tubes, and they sound exactly the same as the stock 5725 tubes.

Interestingly, the supplied 5725 tubes were matched in terms of gain to 0.8 dB. Another thing which I really like about the Tube-02 Pro is that my measurements indicate that the frequency response is consitent to well under 0.5 dB. This is pretty slick. The Tube-02 Pro also produces clean 2nd order harmonic distortion, which of course is the thing which you are looking for if you want tube sound.

Alrighty now. So what are my caveats? You have to be careful about your line input voltage levels since the clean 2nd order distortion will rapidly be overcome by 3rd order distortion if the RCA input voltage level is too high. In other words, make sure that you do not set the volume level on Windows computers above the default 70%, and then simply use the Tube-02 Pro’s volume knob to adjust the volume when you are using headphones or IEMs.Similarly, be careful of your average line level input voltage if you connect this preamp to other audio sources.

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