Fosi Audio SK01 Headphone Amplifier Equalizer Preamp with Bass Midrange Treble Tone Control and Loudness Compensation Portable Class A Analog Amp with 3.5mm 6.35mm Jacks

I bought this to add life and depth to a portable cd player that works great but sounds a little flat, and struggles to drive higher-impedance headphones. This works perfectly, adds a lot more power/volume and the tone controls give a good range of eq. The "loudness" button is also very useful at low volume, the sound quality of my cd player is greatly improved with this little device. Couldn't be happier with it. Also does the same for phone/tablet. Build quality is excellent, feels very solid and durable. Small enough to put in your pocket, if a little heavy.

Fosi SK01 delivers on many fronts, with its versatility. The sound quality is very smooth too. I've used it with my bass heavy Soundcore boom plus 2 Bluetooth speaker, it literally tames the bass, and the ability to also increase/decrease midrange and treble frequencies too makes the speaker sound stupendously awesome, and a joy to listen too ! Results are also very good on my mobile phone, TV and DJ controller. Not so good on my laptop, but that's purely because the laptop manufacturer has skimped on quality audio components, having said that it still sounds great, but with less oomph. All the knobs, buttons and inputs/outputs just work like they should, and my Sennheiser headphones have come alive too. No need to have the volume up too loud either as it delivers great audio quality. Battery life is dependent on how hard you use it, but satisfying all the same. The warning indicator light above the treble knob will flash when the battery power is running low, and show red when you're charging it up. When fully charged, the red light will go out. You can continue to use it when it's charging, but I think it's best to make it charge undisturbed, to prolong the overall longevity of the battery life. The light below the volume knob will flash faster when the volume is too loud, another nice touch My lower quality music files are also enhanced by the Fosi SK01, as I take advantage of the ample frequency ranges provided to tailor and boost the sound where ever it is needed. The sleek rectangular shape is aesthetically pleasing to look at and solidly built, the bottom of the knobs are almost seamless against the main body of the amp, which eliminates dust getting inside I'm not a headphone amp connoisseur so can't compare, and no doubt there are brilliant premium models out there, costing mega bucks ! But Fosi Audio have come up with a winner, that covers many bases, delivering real quality at a price point that doesn't break the bank. One more point… I wish it had Bluetooth capability, to combine with my Bluetooth speaker, to eliminate using leads connecting them together, when I'm out in the public domain. Overall, though, a very well-thought-out product that deserves the accolades and positivity lavished upon it. Well done Fosi Audio 💯 🔥🔥🔥🔥🔥🔥😁

just received this morning, setup was easy, usb from P.C, which carries signal and 5v power, optical from TV used as monitor. Headphones sounded great whether from 4.4 mm balanced or from 3.5. I attached a 3.5 mm audio cable, from the aux out on rear of unit, to my active speakers and all good there too. Controls on top of unit for gain, high/low, a mode selector for optical or USB input, and a volume control knob, with an array of led lights to indicate bit rate and mode. Small yet solidly built. All the connections I need for desktop system are there and at a reasonable price.

The product itself worked fine for a few weeks/months. Then the audio started cutting out completely for minuites at a time and the LED on top turned from green to yellow (This isn't documented in the instructions what yellow means) I think the internal battery for a desktop headphone amp is completely pointless, because when would I use this unplugged especially as it isn't Bluetooth. The issue was caused by said battery. I always had the product plugged in but apparently the battery was discharging more than it was charging when not in use, so the battery was constantly becoming flat and even while plugged in the battery needs to have charge for the device to work apparently. I got in touch with Fosi support and they actually helped out a lot and pretty quickly. They sent me a replacement free of charge and didn't cause any issues. The new product is working better than the first did and sounds clearer. Must have had a faulty first model because the second works fine.

It is a good addition to what I have. Giving a way to tune not only the bass and treble but also on the mid. The price is acceptable considering that it is a cleaning-sounding amp and powerful, too. Able to drive my HD650 effortlessly. I always perfer these volume knobs than the key-presses and these work very well. A happy purchase overall.

Very good dac sounds Great would recommend

Smaller form factor ideal for audio at your desk. Flawless sound, whatever headphones you are using, or passthrough to an amp. Solid build quality, performance and usability. Powered by USB. Balanced or single-ended output... it just sounds really good Sound reproduction is better than you are likely able to hear. Yes, you could spend more on something else... but you really don't need to. Take the money you save and upgrade the headphones that you plug into it, if you need to. Overall, an excellent product.

Have had to edit this.... initially it was great....a few months on and it's just died..... been using it fine and the sound is fantastic..... but woke up this morning to find that sound is on for about 60 seconds, then off for about 60 seconds, then back on..... totally useless doorstop now. One to avoid. Obviously made from cheap components that die quickly.

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Very nice! I use this DAC as a external sound card for two computers, by plugging it into a USB hub into a KVM switch. It takes control of the volume output, so volume control for both the Windows and Linux machine is controlled with the dial. Tweaking the output volume in the Windows OS has no effect on the output volume, however on Linux the OS volume seems to control the gain a bit. But I just set the volume to something which sounds undistorted, and I got the same volume in both OSes. Don't notice delay in sound either. Music playback sounds great. Perfecto.

Tengo varios amplificadores de auriculares, entre ellos alguno de sobremesa, con componentes discretos y en clase A y algún otro de triodos single ended. Pero desde que tengo éste, no he vuelto a usar ninguno de los otros. La versatilidad de poder ecualizar graves, medios y agudos y aplicar loudness (que por cierto está muy bien logrado) hacen que sin importar que cascos utilice, siembre encuentro el balance tonal adecuado. Muy contento con él.

This unit is sufficient as a resolution to enable me to enjoy clean sound through my Beyerdynamic 770 prox ltd. Headphones. My search began with trying out earbuds, nearly 20 pairs put on trial, and it came down to being no options to suit my needs, that aside, Headphones hitting at the quality of Beyerdynamics, leaves nothing left to be desired except for a purely clean signal. This little Fosi Audio unit exceeded my expectations, I give it a solid 5 Stars for the achievement it does meet well. Though there is some lack in the cleanliness of the signal, which I suspect is caused by a conbination of effects, the source originate from a DAC via bluetooth, transmitting from android. The bit rate is no more than 24bits, which is not Fosi Audios fault, secondly the DAC is connected with cheap generic RCAs to 3.5 jack, which is problematic for obvious reasons. This unit will only reveal the truth about any signal put through it, however it does have control features that add a quality to overlook most issues lacking due to low bit rate. Nice Treble, Middle and Bass controls, effective Tone modulation, Gain, and Loudness functions. Fosi could improve these functionalities as they seem to conflict somewhat with each other if all three are enabled, as there is a diminishing niance that takes effect when all three are engaged. The volume control has an excellent ceiling, and over all it passes a pure signal that takes up the sound stage of the Beyerdynics equal to what isbavailable in the signal being amplified. Conclusion, I'm impressed with the build quality it is stylish, all interfaces are smooth and solid, nothing feels cheap or mass produced. It's form factor is intuitively stylish and compliment any small space. Finally, the Price to quality is a bargain!!!

I picked up the Fosi Audio SK02 because my PC’s built-in audio was starting to feel limited, and I wanted a small desktop unit that could drive my headphones better while also handling optical input from my setup. The mix of USB-C, optical, 3.5mm, and 4.4mm balanced outputs looked practical for everyday use without taking up much space. Going in, I expected a clean-sounding DAC/amp that could push regular headphones and some planars without noise or strain, plus basic preamp use. It mostly delivered. The aluminum case feels solid and sits steady on the desk. The big volume knob is smooth, and the gain switch plus LEDs make it easy to see what’s going on. Plug in via USB-C or optical and it just works—no drivers needed on my end. Sound is neutral and clear. Bass stays tight, mids are open, and it has enough power on the balanced 4.4mm side to give harder-to-drive headphones some headroom. I use it for music and gaming, and the quieter background helps pick out details better than the motherboard jack. The line out also works fine if I want to feed a powered speaker or another amp. For daily desk use it’s handy—connect the PC or a TV via optical, switch headphones quickly, and keep the volume independent. Value feels solid for what you get in power and inputs at this price point. A few things keep it from being perfect. The treble can come across a bit linear or bright depending on the headphones. It always needs USB-C power, so it’s not fully portable. And there’s no app or fancy tuning options if you like tweaking on the fly. It met my main expectations for cleaner desktop audio and enough power without complications. Not the last word in refinement, but a practical step up from basic PC sound that does the job well.