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PRICE: $120

PROS

• Solid build quality
• Easy to set-up
• Feature rich
• Comes with a dedicated analogue tuning knobs

• Unique tonal quality
• Smooth but resolving overall sound

CONS:

• Tubes are a bit hard to install
• Can sound a bit too smooth and lacking texture
• EQ knobs can be finicky to use 
• Noisy on IEMs

WHO THIS UNIT IS FOR:

• People who want a unique tone to pair with their headphones
• People who like a warm, smooth and rounded listening experience
• People who want versatile tuning options

WHO THIS UNIT ISN’T FOR:

• People who want a more nuanced and tactile listening experience
• People who want a technical-focused amplifier
• People want to pair this with sensitive IEMs

SHORT REVIEW:

My first tube experience is a success thanks to the GR40. It provided such a unique, warm and rounded sound that is unlike anything I’ve heard. Pairing this with my brighter leaning AVA500 provided me with a lush and rich listening experience. However, it contrasts my usual amplifiers with its smoother transient and tactile presentation and a more intimate than wide instrument and vocal presentation. It’s also not an ideal pairing with in-ears, but damn these sound amazing with the right pairing. RECOMMENDED WITH CAVEATS!

FULL REVIEW:

Sources are a hotly debated topic amongst audiophiles as some swear by the difference that they make to your listening experience while others simply call it “placebo” and “volume-boosters”. Regardless of where your allegance lie, you cannot deny that one type of source does make a difference to the sound. 

Tube amplifiers have been around for a long, long time. And they weren’t just used for amplifying your favorite set of headphones. From radio communication to instrument amplification, tubes have been with us far longer than other audio technology. 

As someone who has not yet experienced the “tube-sound” extensively, the GR40 seemed to be one of the most fitting choices to start this sub-rabbit hole of our hobby. Do tubes really make that big of a difference? If if so, is it any good? 

FOSI, FEATURING THE GR40

Fosi has been one of the prime sources for amplification in the audio space recently and their products have begun to litter the market from the budget conscious individuals to those with a deeper pocket. This assures you that you aren’t going to get something made by inexperienced individuals, rather you’d be getting something more sophisticated and purpose built. 

The GR40 is one such product that was released early December and was priced at $116. Let’s get deeper into this product starting with the build and interface. 

BUILD AND INTERFACE

Upon receiving the GR40, I was greeted by a rather familiar look, shape and feel that other Fosi products have embodied for years. Solid metal construction with the distinct orange knob that lets you know “yeah, that’s a Fosi product”. 

Going deeper, the top features the holes and sockets for the tubes. Fosi graciously provided us with the GE 5654W tube amps which is great considering I do not own any tubes of my own. This should also relay the testing parameter that I’ll be reviewing the GR40 with the included tubes being the only tubes I tested on it. 

In front, we can find the interface which includes the 3.5mm jack, the bass and treble knobs, the LED indicator to show your connectivity and the distinctive orange knob. 

The sides are relatively clean with no features nor interface

The rear features all your connections from the RCA, coaxial, optical, USB C, bluetooth antenna connector and the 12v power plug. 

Below you can find the rubber stoppers to keep your amp from moving about on your table

As far as Fosi amplifiers go, this embodies the well built but functional design that I’ve seen from their products previously. I’ve always loved the little orange knob that they use for their volume knobs as it’s really cute and makes it distinct from the other metal box amplifiers in the market

Setting it up

I personally found the set-up of the tubes itself to be quite tedious but warranted considering the fact that Fosi themselves gave the instruction on what to do when the tubes won’t go in their instructional manual. 

After setting up the tubes, it’s all a matter of plugging the included 12v adaptor and choosing from the multitude of inputs and it’s all set. 

Fosi instructs that you let the tubes warm up for a few minutes before plugging in your headphones and listening to music, so I followed that every time I turned the device on.

Setting up the bluetooth is also quite simple as the GR40 searches for new devices by default and all you have to do is to turn on the bluetooth of your device and connect to the GR40.

Features and Specification

As for features, the GR40 packs a decently feature-rich package that I don’t usually expect in amplifiers of this kind. 

First, let’s talk about connectivity. The GR40 features wired input of USB, Optical and Coaxial while featuring Bluetooth Wireless input. As for output, this features RCA and 3.5mm Headphone. This means that you can use this as a pre-amplifier through the RCA or straight amp for your favorite headphones. 

As for its decoding sampling rate, it is capable of decoding 32bit 384kz files and up to DSD256 through its ESS9028Q2M DAC

As for bluetooth transmission, it is cable to transmit through SBC, AAC, aptX, aptX HD and aptxLL. 

As for output power, the GR40 is capable of 250mW @ 32ohms on it’s 3.5mm SE jack. 

Usage

I’ve never found these kind of amplifiers to be tedious to use whatsoever. They’re plug and play and does not require fiddling. 

That is except for the fact that this thing has dedicated bass and treble knobs. I’ll talk about its effect on the sound later, but I want to highlight the fact that I absolutely love this level of customizability in your sound experience that allows you to manually tweak the bass and treble levels without the use of software. It’s not often that you get analogue knobs in amplifiers, even from Fosi with the likes of the SK02 having an infinity knob. 

Regardless, I think more brands should release amplifiers with dedicated bass and treble knobs to fiddle about. I know hardcore audiophiles wouldn’t care for this, but even they’d appreciate if they can tweak a bit of the sound on the stop without the need for virtual EQs. The only gripe I would give this is that the bands that it changes seem to be a little bit much depending on the headphones you plug. 

As for its connectivity, I found it to be stable enough for most scenarios I tested this on and I had no issues connecting any of my devices. I had no issues with playback and the decoding quality is pristine.

As for the smaller stuff, I found the interface and physical connections to be solid and well-made and I don’t feel anxious with plugging and unplugging as well as turning the knobs a little too much. It’s just a Fosi thing to make really well-built amplifiers. 

Sound and Output

Finally, let’s talk about the sound and output of the GR40

First and foremost, let me lay down all of my testing parameters below;

Main Headphones Tested:

• Audiotechnica ATH-AVA500
• NiceHCK EB2S Pro
• Moritz Paradise

Sources Paired with the GR40:

• PC (through USB C)
• HiBy R3 (USB C and Bluetooth)
• Samsung A54 (USB C and Bluetooth)

I decided to only test its solo DAC/AMP capabilities because I personally would only use this as is. I have the option to pair this with another amplifier, but I’d argue that’d ruin the purpose of the device. 

Now how does it sound? As someone who’s never properly heard a tube amplifier before, the best way I can describe this thing is it sounds very warm and rounded. Like a balloon filled with warm air. Odd way to describe, yes, but one that strikes perfectly how I feel towards how it sound.

I’m so used to delta-sigma DACs that emphasize the details, treble and “technicalities’ of the headphones you’d pair with the amplifier that the GR40 initially weirded me out. 

This is partially because of the equalizer being a very new feature for me on portable headphones. I’ve had my fair share of analogue equalizers on speakers, but never on headphones. And when pairing this with my favorite ATH AVA500s, I found that it unlocked a very unique tonal presentation I haven’t heard my AVA500s done before. 

The bass actually sounded thick, borderline too thick with the bass knob poistioned at 12 o’clock. The treble needed to be cranked a little earlier at around 10 o’clock to balance the natural brightness of the headphones, but the sound was genuinely unique. 

One aspect that truly weirded me out was the oddly strong yet smooth attack of the treble, especially when levelled with the bass. I’ve always expected that tube amplifiers embodied warmth and musicality, but the treble hit pretty hard even for my tastes. A little too much, but nothing that the knob couldn’t tweak down. 

However, this also means that you aren’t going to get a truly “neutral” tone by default and it will require you to tweak the sound in such a specific way that you might as well have gotten a standard amplifier. 

Regardless, I do believe that this is what makes the tube amplifiers and the GR40 so special. This kind of sound is so refreshing to hear after all the samey dongle DACs and amplifiers littered in the market and provides you with a sound that you might not have heard before on your favorite headphones.

However, I want to reiterate the fact that these are best pair with headphones and higher impedance gear. This is because, unfortunately, the noise level of high sensitivity and low impedance in-ears is quite nasty and not something I’d deliberately listen to. It’s audible to the level that people with sensitive hearing would probably not enjoy like I did while playing this through my Moritz Paradise. 

Thankfully, pairing this with the NiceHCK EB2S Pro was satisfactory with its higher impedance allowing for a noise-free listening experience. However, the pairing of a rounded tone and the EB2S Pro’s already smooth tonal presentation isn’t ideal. 

This is why I ended up using the AVA500’s the most with the GR40 as I genuinely got addicted to the warmth it brought to the usually bright and analytical AVA500s. 

One gripe that some people, including myself, might be turned off by at first is its rather lower output numbers. 250mW @ 32ohms isn’t necessarily impressive, even for 3.5mm with the likes of Fiio KA11 outputting similar numbers for such a tiny package. 

However, I’d argue that it’s not necessarily the output numbers that should matter. Rather, the quality of output has to be the thing that people should care about. In the case of the GR40, the output is fantastic for what it tries to do and even gives you the option to tweak it to your liking. That’s the one thing that makes the GR40 such a stand out with all the other sources I’ve tried. 

Obviously, it’s not what you’d call “perfect” in the literal sense of the word because that doesn’t exist. It leans on the warmth a little much to the point where you’ll need to lower the bass to the level of being almost absent depending on the headphones you pair this with. The treble in contrast is quite powerful and will require you to tweak the treble a bit more than the bass in my experience. This rounded tonality also contributes to this not being a very “technical” sounding amplifier compared to even something like the Fosi SK02. The warmth in the sound also gives the GR40 a more center than wider stage that the AVA500 really honed into as the AVA500’s stage is quite lackluster on its own but further compounded by the GR40’s somewhat claustrophobic and center-staging presence. I wouldn’t really call this a con in of itself as an intimate listening experience can be quite satisfying, but it’s worth noting for those expecting an expansive stage. 

However, it’s such a unique and personality-filled sound that no other source I’ve tried have given me. That’s what keeps me hooked and listening to the GR40 despite having more “revealing” and “technical” sources because this is the kind of sound that can only exist in tube amplifiers as versatile as the GR40. Listening to music without worrying about detail retrieval, stage and all those qualities that many audiophiles have grown to overuse and overemphasize is refreshing. I can just sit down with maybe a nice cup of tea or coffee and lay back while listening to my favorite tracks with my favorite headphones. It’s a fuss-free listening experience that doesn’t distract you from enjoying music, granted you’ve set it up to your tastes. 

CONCLUSION

In some ways, the GR40 is the perfect tube amplifier to start this “tube-life” journey because it offers so many features and versatility with how you can use and pair with it. I’m definitely looking for other tubes to “tube-roll” with the GR40 once I get the time to actually play around its more intricate features.

But this journey is something that I know isn’t for everyone. Despite the ability to tweak the sound through its dedicated analogue tuning knobs, it’s still such a rounded and musical listening experience that those with a more refined and technically-oriented taste would not be able to enjoy. Top that with the fact that this is basically useless with high sensitivity in-ears as it limits its market to those specifically looking for tube amplifiers.

As for amplifiers go, I still highly recommend this for being such a compelling, well-built, feature-rich and easy-to-use device that’ll give you a warm, lush and rounded listening experience to your favorite pair of headphones. 

Thank you for reading my full review on the Fosi GR40. If you would like to buy one, consider using the non-affiliated link below:

Fosi Auido Shop：https://bit.ly/fosigr40

Amazon US：https://amzn.to/4fCM3CM

Ebay：https://ebay.to/4fBVEcZ

Aliexpress：https://s.click.aliexpress.com/e/_DDjncih