Fosi Audio Box X4 Phono Preamp & Headphone Amplifier

My Vinyl never sounded better – Have been running a ART DJ preamp II for 5 years (it died) and replaced it with the Fosi X4 vacuum tube preamp (2 vacuum Valves) designed primarily for MM (moving magnet) phono input and processing which is my prime use. It will take a line input through 3.5mm plug as well. There is any number of small, vacuum tube type preamps on the market, but Fosi seems to make a good range and get good reviews for their products, so I went with the X4 - it is a delightful little pre amp, looks a little "retro" with the tubes sitting in the middle of the box, which in form is small and compact. The build quality impresses immediately and its very well constructed - small metal box with very sturdy RCA inputs, connections and control knobs - there is an on / off combination volume control, bass and treble control knobs and 3.5mm input socket on the rear and 3.5mm headphone socket on the front.

The vacuum tubes, whilst they glow when turned (as an indicator of power on) on are also backlit with LED's under the base which gives them a nice warm glow, they look nice when on. There is no power on indicator light but the tubes glowing indicates its on. Power input is 12v adapter, also good quality. The tubes themselves cost up to $30 a pair so the overall cost of this preamp is a bargain - the tubes are 7-Pin 5654W Vacuum Tubes for Tube Amplifier Preamplifier (GE) and are readily available - the lifespan is rated at up to 10,000 hours (preamp tubes), power tubes are rated around 1,000 hours)

The vacuum tubes are supplied in the package and have to be fitted before use - this is the only slightly challenging part of installing the Fosi - it takes a fair bit of pressure to seat the 7 pin tube in the base - I was concerned I might break one with the strong pressure being applied but need not have feared as they went in ok. With the preamp connected I began to play my vinyl - the response was amazing.

With a tweak of the bass and treble on both the amplifier and the preamp and the volume control (gain) set at about 3/4 clockwise the sound emerging from my system was both an improvement on the original preamp and the preamp built into the turntable and amplifier which I had experimented with for comparison.

The audio technica turntable has MM and line output and the amp built in phono input. By running the MM output from the turntable into the preamp and then line input to the amplifier I am now getting improved stereo separation and wider sound stage with improved bass as well, which had bothered me with the previous set up.

Couldn't be happier with this little gem !

Basic specifications:

Input Interface: MM turntable input, 3.5mm AUX input Power source: 12V DC input (power pack supplied) Output Interface: RCA output, 3.5mm headphone output. Output: Active(powered) speakers, Amplifier, Headphones. Applicable headphone types: 16 Ω - 300 Ω Output Voltage Level: 1kHz and 650mV. SNR: ≥ 70dB. THD: ≤0.1%

Pros: very well built, excellent quality considering the price as well Perfect for MM phono processing Good control with volume, bass and treble adjustments Vacuum tubes definitely create a nice warmer sound stage Very clean output, minimal noise

Cons: No cons as such - installing the vacuum tubes is "interesting" My vinyl sounds even better for them though !