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

Customer support:- I should mention this that initial product i received had tone button issues. Whenever I pressed it noise occurred. I thought it was fine as it only happened when music was playing. Later on it added channel imbalances also when pressed. So i emailed fosi support about this and they asked for a video of issue that i was having so that they can understand what issue was. Later support team sent a new replacement unit from china and i got it within 3 weeks. And new one is super good and no problems whatsoever. Initially i was very skeptical about what to do when fosi products start having issues. But after having to talk to guys with fosi support team, I am happy with their response and kind support. I really like their fosi za3 amp so waiting for their newly launched zd3 dac to arrive in india and then buy both as fosi have value for money products.Build of sk-01 is super nice. All metal and feels cold. Knobs rotation is quite nice. Even after using for months its good and no paint chipping off anywhere.Terminations:- Has a line in port at back with a line out mentioned below it which is actually a pre-out as volume can be controlled on this one and a 3.5mm and one 6.35mm port at front. The only thing I really think it should have had is a balanced 4.4mm out so that i could connect my good iems/headphones. Still 6.35mm and 3.5mm are implemented good and they are sturdy.Sound:- I would say if u got some headphones or iems that have some tonal imbalances, this fixes that. Also no noise is audible even on high gain. Some reviewers mentioned it having it a slight noise but thats on some really sensitive iems and u wont have those for casual listening. I got it to have more treble and bass gain for my sony wh1000xm4 headphones. Even though these headphones cost like 30k they arent good. People just don’t know how music should sound like and even me also didn’t knew. Recently I learned some audio professionals info and got to hear how music should sound like and i am impressed. Bought Kiwi ears Cadenza from headphonezone site india and it costs like 3k and still sounds way good that xm4. Now i regret not knowing about good audio quality products at such price exists for a long time. So used SK-01 to match clarity of those iems and since its a headphone its drivers are big, so bigger soundstage. Amp inside of it is nice as its way overpowering for most headphones. Its class a amp i think, not sure maybe check product description. Still it sounds good. Battery lasts around 5-6 hrs when fully charged. Bottom led in my opinion is not useful as it sucks battery power which instead can make device last more longer hrs.Final verdict:- Its a good product i would say for tone controls as aux port or usb c adapters are not that good in audio quality compared to external dacs and this sk-01 can add more power and tonal balances as per your need for any iems or headphones u got. Not only u can add but decrease tones also so do remember that. It can decrease harshness on some iems also. Plus its battery powered so portable. So maybe look into frequency graphs when buying next audio products as most audio professionals don’t like tone controls as they got high priced equipments which are neutral in tonality. Music is personal and for normal priced headphones or speakers or anything, this product is well value for money. Its clarity, build and versatility makes it a unique product that can be used with anything. Price is bit on higher side but u can get it for 7k using card discounts and at that price its good i would say. Not a product u must have but one that u can have for fixing tone controls and add in ur audio products arsenal.

Appearance-wise, it is very elegant. Hefty well-built Design.All Product Features and Connectivity, are as described in the Product web page.Only thing I can add is 'How does it Sound" : Unbelievably Good.I would have been happy, if a larger Battery was provided.

Wonderful sound quality

It instantly enhanced my Sennheiser HD 650 sound output. It is sturdy and sits firmly on my desk. The sound is pretty flat I must say, great in the studio. I do find myself boosting the lows occasionally because they just sound so sweet. No problem whatsoever.

Was looking for a way to quickly adjust the EQ physically without going through any software, this solves the problem perfectly. Initially bought the Fosi Audio K5 Pro, but returned it due to inadequate performance, this one is way better even though it costs a bit more. Very satisfied with this purchase.

Amazing sound quality but price little high

I would not call it a bad product but the performance is not that one can call "WOW". I mainly bought this to drive my Sennheiser HD599 (50 ohms impedance) headphone. Fosi audio has enough power to drive these headphones at low gain setting. I do not use "tone defeat" and "loudness" button as I find the use of bass, mid and treble to be more appropriate for my personal listening. I have not tried this as a preamp only as I do not have a proper power amp to see it's real potential. However I hooked it on to an integrated class AB amplifier just to check the tonal quality. Even though the specs say it is Class A preamp it falls short of the fine and clear tonal quality of the NORGE/Cambridge Audio integrated amplifier pre-amp section. However I feel this Fosi audio SK01 will perform well as a pre-amp if matched with a class D power amp of Fosi audio or other similar brand models.Currently I am using this for watching TV programs like movies, web series. A blue tooth receiver takes signal from the android box and give wired signal to this device (line -in) and finally using a wired headphone connected to this device. These are no complaints as such on this method of usage. The sound is very natural and not enhanced in any way. The best part is that this can be used on backup battery as well as connected to the electrical connection.3.5 stars ratings - better then average.