[Prova d'ascolto] Fosi Audio P3 - vacuum tube line preamp with Bluetooth and headphone output

Product: Fosi P3 - line tube preamp
Manufacturer: Fosi Audio - China
Approx. price: ±€100
Reviewer: Lucio Cadeddu - TNT-Audio Italy
Reviewed: February, 2024

Foreword

Shortly after the release of the ambitious V3 integrated amplifier that I reviewed about 8 months ago, Fosi Audio decided to please the customers who asked for more inputs, Bluetooth, headphone output and, why not, add two little colored vacuum tubes. The same customers were hoping to get something to make the sound of the V3 smoother (not that this was really needed!) by adding some fancy looking vacuum tubes. Hence, instead of designing a V3 with multiple inputs and remote control, which would have been THE thing to do, here comes the P3.

A closer look

The P3 is a small line preamplifier, with two good American GE JAN 5654W tubes, a Bluetooth 5.1 input served by a Qualcomm QCC3031 chipset which allows aptX HD and aptX LL connection, a single line input, a line output, an AUX OUT for the subwoofer, headphone output and tone controls. The components are of medium-high quality, low ESR Chinese capacitors and an audiophile-grade Elna capacitors bank. The potentiometers are all linear of the B50K type, although Fosi claims they are A50K. The pair of Made in USA tubes alone costs almost €30 on Amazon and €15 on Aliexpress. Impressive, considering the price of the whole preamp! The internal construction is very accurate. It lacks a remote control, which would have been useful, and there is no second line input or digital input. Then you have tone controls: ±10dB on the bass (!!!) and ±6dB on the treble.

The aesthetics are refined, with a cyan backlight that glows from underneath the two vacuum tubes, and the level of finish is good. The external power supply provides 12V at 1.5A. Obviously, the P3 can be used as a stand-alone line preamplifier, connected to a power amplifier. My tests, therefore, were carried out in two ways: P3 as a pure preamplifier and P3 used upstream of the V3 integrated amplifier.

Claimed tech specs

All that glitters is not gold...

When Fosi Audio designed the P3, the intent was to use it upstream of the V3. I humbly pointed out that from a logical and technical view it would be a suicide to put two volume potentiometers in series, but they didn't seem to care. I set the volume of the V3 to maximum, so to limit its influence, and be able to evaluate the real influence of the P3 on sound quality.

A small, perhaps obvious, premise: for an audio signal, the fewer stages it passes through, the less it is corrupted. The V3 didn't need to be pre-amplified, it worked (very well!) on its own. Adding an upstream stage, with its circuits and those two tubes could not be a painless choice. The V3 alone sounds better: much better. Indeed the P3 adds something, but this something is coloration, distortion, compression and limiting at the extremes of the audio range. Even the image shrinks, especially in terms of height and depth. The dynamics collapse, and there is no longer that beautiful rhythmic verve that distinguishes the V3 performance.

Some will find this artificial distortion almost pleasant, in which case I invite you to visit some concert halls, to hear what the real sound of the instruments is. From what I read around, there seems to be a great need for this. Now, were you hoping to add a sweet, warm, tubey note to the V3's precise, surgical sound? Oh dear! There's nothing tubey about the sound the P3 generates. So: if you don't like the V3 as it is, look for something else, but don't damage its sound with added distortion, as it doesn't deserve it. Distortion is good for electric guitars.

How can someone say the P3 improves the sound of the V3 is something that is completely beyond my understanding. But why am I surprised? I read a review of the P3 - in a magazine, (not the usual forum chatter, FB group or deaf YouTuber channels) - where the author states that the zero point of the tone controls is obtained not with the central position (like Fosi states) but by rotating the two knobs completely to the left. So he wrote the review of the P3 with the bass range being attenuated by 10dB and the high range by 6dB, and under these conditions he claims the P3 sounds good. That's beyond belief to me.

A little disheartened, even if the result was largely predictable, I tried listening to the P3 connected to a power amplifier, in comparison with other preamplifiers of the same price, those of the shootout test I published some time ago; more precisely: the Akliam/Domelec tubed preamp, the solid state BRZHIFI VOL-02 preamp and the passive Tisbury Mini and BRZHIFI PAP-FV3-2 preamps. The P3 positioned itself mid-table, between the Domelec tube preamp and the solid state BRZHIFI preamp. Unfortunately, the comparison with the Tisbury Mini was devastating for the little one with the cyan eyes. It's true that the Tisbury costs a bit more, but the comparison is merciless. The P3 loses, as did the other three preamps, practically across the board: transparency, fullness and extension of the low range, cleanliness, detail and sound stage.

Its sound, compared to the Tisbury, is small, harmonically poor, dynamically compressed and unrealistic. You might think (hope?) that it's euphonious, given that there are tubes...but no, it's not even valve-like in the best sense of the term. It is not warm and smooth, it is not harmonic or tonally rich. In practice, all the features that one would expect from the presence of the vacuum tubes...are missing. Not only, at times you can perceive hints of compression and distortion in the most difficult musical passages, which the Tisbury manages with ease, like a much more expensive preamp.

The difference between the two preamps is not in terms of subtle nuance, but more along the lines of “OK, let's play one more record” and “no, turn everything off please”. With the Tisbury the wish to continue listening doesn't vanish, with the P3 you quickly get tired and bored. The price difference, taking into account this astounding difference in performance, is absolutely negligible.

N.B. Obviously, when I talk about an abyss of difference, let's try to understand well my words: it's not as if you're listening to them in a desktop system with inexpensive loudspeakers next to the PC monitor and a €50 amplifier you'll notice the difference! You probably wouldn't perceive any difference at all. The comparison was made with high-end components, in an acoustically tuned room. Only in this way does it make sense to discuss differences, when we are in a position to highlight them. In the absence of these conditions, it would be much wiser to remain silent, since your doctor has not ordered you to be an audio reviewer. So, if the difference between the two is not audible or does not seem so evident to you, the system and the room are not up to the task. Assuming your ears work.

And now for some positive notes: you get a decent headphone output, which can always be useful, the tone controls, which are also useful for correcting any environmental, speaker or recording deficits and the possibility of playing around with different tubes.

Remarks and complaints

Conclusions

The Fosi P3 is a component that might find its place in the market, but honestly I'm not sure it will. It doesn't add line inputs to the V3 (just Bluetooth), it doesn't offer a remote control, it doesn't improve the sound (it couldn't have!). So what's the point? As a minimal preamp connected to a power amplifier, perhaps, it might be useful; after all, it's inexpensive, cute and well made. Furthermore, if you want to enchant your friends with two little tubes with a sexy cyan backlight, without breaking the bank, then go for it! Otherwise, should you need a preamp that costs little and doesn't add too much of its own to the music that passes through it...look elsewhere!

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Fosi P3 - tube line preamplifier

All that glitters is not gold...

Foreword

A closer look

Claimed tech specs

All that glitters is not gold...

Remarks and complaints

Conclusions