Fosi GR70 Review: Tube Sound for Just €200!

We were quite curious to test the affordable tube headphone amplifier and preamp from Fosi, and after a few weeks of testing we can finally share our thoughts on the GR70. This is a preamp and headphone amp that, at around €200, sits in the entry-level tube category—a segment that isn’t very crowded, since it’s not easy to deliver quality tube devices at a low price.

Features and Functions

The GR70 works both as an amplifier and a preamp. It features RCA inputs and outputs and two headphone outputs (6.35 mm and 3.5 mm), along with front knobs for adjusting bass and treble—very convenient and fun for those who enjoy shaping the sound to their liking. The large volume knob sits on top of the device; it’s smooth, click-free, and very well made.

As you can see from the photos, the tubes are exposed on the top side of the unit. On the sides, there are circular ventilation holes (a solution Fosi has used before), through which you can see a nice copper-colored perforated grille—now a distinctive aesthetic feature of the brand.

A very important note: this little device has plenty of power. Switching the front toggle between Hi-Z and Lo-Z allows it to drive almost anything with ease. According to official specs, one mode is suitable for headphones up to 120 Ohm, the other up to 300 Ohm. We tested it with some demanding headphones, and power is definitely not an issue—unless you’re using extremely high-impedance models.

NOTE: the switch should not be interpreted as Hi = high gain and Lo = low gain. Instead, Hi is only for headphones above 120 Ohm, and Lo is for everything else. Always check your headphones’ impedance and set accordingly.

Let’s return briefly to the connectivity options, because they’re worth highlighting. As mentioned, it works as both amp and preamp and uses RCA connections—but here are some practical examples. You can use RCA-to-RCA cables with DACs and CD players, connect PCs or mobile devices using 3.5mm-to-RCA cables, link it to powered speakers, or connect it via RCA to a power amplifier driving passive speakers. This gives you a clear idea of the device’s versatility—especially considering its €200 price tag.

The unit uses four tubes: two 5654W and two 6Ж4/6Ж8, arranged in a two-stage amplification design. Output power reaches 300 mW, with 1.2V RCA output.

In the box, you’ll find everything needed to get started: power cable, tubes with protective glass covers, a good headphone cable, and a printed user manual. You likely already have RCA cables, but if not, you’ll need to purchase them separately.

A couple more notes before discussing sound: let the GR70 warm up for about a minute before listening. Also, never disconnect cables while the device is on—first turn the volume all the way down to power off, then unplug cables.

Now, let’s talk about sound.

How the Fosi GR70 Sounds

We tested the amp with various DACs and headphones—mainly Grado, Hifiman, and Fosi i5. We also paired it with higher-end DACs like the Hifiman EF600 (with excellent results), but our main focus was the Fosi Audio ZH3 + GR70 combo. This setup, excluding headphones, costs around €400—less than many entry-to-mid-level DAC/amp combos that easily reach €500–600.

As expected, ZH3 and GR70 pair extremely well, and they’re also great companions for the Fosi i5.

The overall sound signature leans warm, but not excessively. This warmth comes with impressive detail retrieval, strong dynamics, and a pleasing dryness—resulting in a rich, enveloping sound. The soundstage is fairly wide, though not as expansive as more neutral, analytical setups. Vocals have a warm, intimate, almost caressing quality, enhanced by good instrument separation and accurate spatial placement.

Together with ZH3 and i5 (and similar planar headphones), the GR70 delivers an energetic sound with punchy, detailed, fast bass that still remains smooth. The bass never overwhelms the other frequencies; instead, it blends beautifully into the mids, creating a cohesive and engaging presentation. Detail retrieval is especially noticeable in the midrange, which stays full and smooth.

In our opinion, the default bass setting is excellent. Increasing it adds depth and fullness—worth trying with genres that benefit from stronger low-end presence. High frequencies are pleasant, smooth, and detailed, with no harsh spikes. They retain that warm character, giving vocals—male or female—a very intimate tone.

We found that slightly increasing the treble (just above the 12 o’clock position) brings vocals and highs forward, creating a very pleasing effect worth experimenting with.

The GR70 performed well with virtually all devices we tested, excelling even with demanding headphones like the HE600. However, we strongly recommend the ZH3 + i5 combo, as the synergy is excellent and each component offers outstanding value.

Even without considering headphones, ZH3 and GR70 together deliver performance that challenges €600–650 DAC/amp units—while also offering the unique appeal of tube amplification, beloved for its warm, emotional sound.

Even considering the GR70 alone: while we haven’t tested many budget tube amps, we doubt there’s currently another model offering this level of versatility and performance at €199. Compared to slightly cheaper alternatives that lack preamp functionality, the GR70 is clearly the better investment.

Conclusions

We’ve been highlighting Fosi’s steady product improvement for some time now—and this is another step forward. Paired with the ZH3, this little gem delivers incredibly good sound, with a warm, full signature that remains detailed, energetic, and well-balanced, offering solid imaging and a nicely intimate soundstage.

The GR70 offers exceptional value for money, and its preamp functionality adds versatility. If you want to feel the charm of tube sound on a budget, this is a highly recommended option.