Fosi Audio P3 – Review

Fosi Audio P3

 | Headphone Amplifier | Bluetooth Amp | Vacuum amp/pre-amp |

Fosi Audio P3, a brand new headphone Vacuum amp from Fosi Audio.

The Fosi Audio P3 might look small and innocent but the little guy is actually a rich-featured vacuum tube headphone amplifier, Bluetooth amplifier and pre-amp.

The model was launched as a fundraising campaign that successfully achieved 10 times of the pledged goal.

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Fosi Audio P3 Review

Tests & Scores


Accessories & Packaging

The unit comes with the typical Fosi Audio packaging with enough foam protection inside to ensure a safe shipping of the device.

Inside you get:

• 1x PSU
• 1x BT antenna
• 2x Vacuum tubes




The headphone amp has a very small size despite it’s respectable power and the 2 tubes. In fact, the P3 is shares the dimensions of the speaker amp sibling, the V3.

A metal ring on the top cover, right around the base of the tubes, has a good-looking orange accent that gives a hint of color to the all-black main theme of the amp and if you stack it with the Fosi Audio V3 (with the orange knob), you will have an aesthetically matching couple.

A cyan light is placed on the base of the tubes connection that illuminates the tubes when the unit is turned on, giving it an aesthetic popping detail that contrast with the orange glowing from the tubes themselves; this light details are even more noticeable on dark environments.

This same light has a very smart double function, illuminating also the 3.5mm headphone jack from the inside; being so, you can see and find the jack even on a completely dark room.



Operation & Control

The unit is fully controlled by 3 knobs and a metal switch that works as a power and mode switch.

From left to right you find these knobs:

• Treble control
• Volume control
• Bass control

The volume knob has a very smooth movement with a stepless rotation range of 270 degrees while the treble and bass control knobs have the same 270 degrees of range, the movement has a slight scratchiness feedback when rotating them and a clicky stop on the exact half of the rotational range, allowing a clear point when the treble/bass control is set precisely to the middle.

This might be a personal preference, but there is something about analog controls like old-style classic knobs that are just unbeatable against digital settings and menus when regarding the fun of controlling bass/treble and volume while listening to music.



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Construction & Build

The amp has a full metal build that looks and feels very rugged and much more solid than the price might suggest.

From switches to knobs, everything is extremely well put together, seeing even knobs that do not wobble a single bit.

On the bottom, the unit is equipped with 4 rubberized feet that have a silicone-degree of grippiness, making it highly stable as a standalone unit over a desk or stack above other audio-component.




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The P3 amp has one single 3.5mm headphone connector on the front panel and all the remaining I/O connections on the back panel.

In total you get access to 5 input/output connections, including:

• RCA input
• Bluetooth

• RCA output
• 1x aux out
• 3.5mm headphone


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The amp is equipped with 2 GE 5654W tubes, classic, vintage tubes that have been around since ever.

The hot-plugging of headphones did not show strong popping sounds but a slight hint of noise is heard when doing it and having a very high volume preset.

Volume control has a very responsive and sensitive movement but consider that the amp outputs a lot of power right away from the first degrees of rotation. So, do not go all the way in with the volume knob, connect your headphones and start easy and from the 0 position.

Despite seeing that the bass and treble knobs indicate “+” and “-” readings, the amp does not have negative bass and treble control; the device starts from a zero position for the lowest “negative” and anything above will be boosted dB of bass/treble; therefore, the clicky middle position corresponds to half of the max boost and not the zero position – basically, this means that you can boost bass and treble but you cannot tame them down below the zero/flat start; yet nearly all casual listeners look after boosting bass/treble and not reducing them.

Our tests revealed that bass control added a massive amount of dB boosting, even turning an average bassy headphone into a skull-crushing bass experience. Our measurements revealed up to 12dB of bass booting and 6dB of treble boosting.

Both bass and treble control were well-tuned to act over ranges that allow a massive boosting but without becoming a messed-up over boosted mayhem.

Furthermore, our measurements of the Fosi Audio P3 showed a flat frequency response making it a versatile headphone amp that allows both a clean audio experience with a typical vacuum tube” flavour when used flat and a personal tuned sound when playing with the bass/treble knobs. The tube amp design allows the P3 to provide a warmer tube tint due to the harmonic distortion added by the tubes amplification.

We mentioned during the Operation & Control section the “scratchy” feel of the treble/bass knobs, yet this scratchiness is only felt as a tactile feedback while absolutely no scratchy noises are heard nor transmitted over your sound output – also the potentiometer has no scratchy noises.

With a max RMS output power of 250mW, the P3 was more than capable of driving any popular commercial and classic headphone, from in-ears to over-ears, the amp never fell short of power.

On top of that, the little amp hides beneath the surface some Hi-Fi specs and components such as:

  • SNR >103dB
  • Dynamic Range 104dB
  • Noise floor 64uV
  • Crosstalk 95dB
  • Qualcomm QCC3031 Bluetooth chip with BT 5.1
  • Bluetooth codecs including SBC/AAC/aptX/aptX HD/aptX LL



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Scores Scores

Fosi Audio P3 Scores

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Frequency Response (raw)

Fosi Audio P3 Frequency Response Curve and measurements

Fosi Audio P3 frequency response curve
Fosi Audio P3 frequency response curve


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Fosi Audio P3 Technical Specifications

• Input: RCA line-in, Bluetooth 5.1
• Output: RCA line-out, AUX out
• Bluetooth Chip: Qualcomm QCC3031, supports SBC, AAC, aptX, aptX HD, aptX LL codec
• Headphone Impedance Support: 16Ω-300Ω
• Frequency Response: 20Hz-20kHz
• Control Knobs: volume knob, treble & bass tone control
• Tubes: 6ж2 (real tube amplification)
Power Supply: 12V/1.5A

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Fosi Audio P3