The Apos Gremlin is one of the most interesting headphone amplifiers you can buy for the money. It is a fully balanced Class A tube hybrid in a clear acrylic case. A matched pair of 12AU7 tubes sits at its heart. XLR and 4.4mm connections sit at both ends. Most budget tube amps give you a tube and a volume knob. The Gremlin gives you a balanced signal path from input to output, which you normally find a tier or two higher.
This Apos Gremlin review looks at who that design suits. It is a great fit if you have a source with balanced outputs and want tube warmth with transistor control. It is a poor fit if you need RCA inputs or a built-in DAC.
Quick answer: The Gremlin is a strong buy if your source has balanced outputs and you want a tube-flavoured amp with real power. It is rated at 1,250mW into 32 ohms and covers 8 to 600 ohm headphones. That handles most dynamic headphones and many planars. Skip it if you need RCA inputs, a built-in DAC or a cool, quiet amp for very sensitive IEMs. For a conventional layout with single-ended jacks, compare the xDuoo MT-02 and the Fosi Audio GR70, or browse the tube headphone amp roundup.
Who the Apos Gremlin Is For (and Who Should Skip It)
The Gremlin is for listeners who want a serious desktop amp without a serious price. It suits anyone moving into balanced listening. It also suits anyone who likes to see how an amp is built, because the case is clear.
It is a good fit if you:
- already have a DAC or source with XLR or 4.4mm balanced outputs
- own demanding dynamic headphones or some planars
- want to tune the sound by swapping 12AU7 or 6922-type tubes
- like the look of an amp with its parts on show
Skip it if your source only has RCA outputs. Skip it, too, if you want a built-in DAC. If you are still deciding whether you need an amp at all, start with our guide on whether you need a headphone amp.
Apos Gremlin: Key Specifications
Apos Gremlin Class A Balanced Tube Headphone Amplifier
- Type: Hybrid: tubes in the preamp stage with a Class A buffer output, fully balanced
- Tubes: Matched pair of 12AU7 included; designed for 12AU7 or 6922 types
- Output power: 1,250mW at 32 ohms
- Headphone range: 8 to 600 ohms
- Frequency response: 20Hz to 50kHz (±0.5dB)
- Distortion (minimum): 0.01% at 1kHz
- Signal-to-noise ratio: 110dB
- Channel separation: 104dB at 1kHz
- Inputs: Balanced XLR and 4.4mm
- Outputs: 4-pin XLR and 4.4mm balanced headphone jacks
- Power: 18 to 24V DC adapter included
- Case and size: Clear acrylic; about 5 x 3.25 x 2.5 inches (127 x 83 x 64mm), 2.09 lb (0.95kg)
- Warranty: 1 year
- Fully balanced Class A design, which is rare at this price
- 1,250mW at 32 ohms and an 8 to 600 ohm rating cover most headphones
- Replaceable 12AU7 or 6922 tubes let you tune the sound over time
- XLR and 4.4mm connections at both ends, with the power adapter included
- Very strong owner ratings on Amazon
- Balanced inputs only, with no RCA and no built-in DAC
- Runs warm, and the clear case leaves the tubes and circuit on show
- A newer brand with a shorter track record than Fosi or FiiO
AmplifierZone Editorial Rating
A balanced Class A tube hybrid with real power and replaceable tubes, aimed at listeners with balanced sources. Limited by its balanced-only inputs and warm running.
Reviewed by AmplifierZone Editorial Team
The Balanced Class A Tube Hybrid Design
The Gremlin is a hybrid. The tubes sit in the preamp stage, and a Class A buffer drives the headphones. The whole path is balanced, so the left and right channels each get their own signal path through the amp. That is rare at this price, so it deserves attention.
The clear acrylic case shows the tubes, the capacitors and the XLR socket. It is a small desktop amp, about 5 by 3.25 by 2.5 inches. It looks like a project board rather than a polished showpiece. That suits the price. Our tube headphone amps explained guide covers the hybrid idea in detail. Tube vs transistor amps covers the trade-offs.
The numbers support the design. For example, Apos lists 1,250mW into 32 ohms, a 110dB signal-to-noise ratio and 104dB channel separation. Distortion is listed as low as 0.01% at 1kHz. Frequency response runs from 20Hz to 50kHz within ±0.5dB.
What You Need to Plug Into a Balanced-Only Amp
The Gremlin takes balanced inputs only, so check your chain before you buy. It has XLR and 4.4mm inputs, and no RCA.
Your source: you need a DAC or source with XLR or 4.4mm balanced outputs. Many mid-priced desktop DACs offer them. A source with only RCA outputs will not connect without an adapter cable.
Your cable: choose a cable that matches both ends. XLR to XLR and 4.4mm to 4.4mm are the clean choices. Mixing connector types needs an adapter, so avoid it if you can.
Your headphones: the Gremlin has a 4-pin XLR and a 4.4mm headphone jack. Headphones with a balanced cable plug straight in. Others, however, need an adapter to a balanced jack.
If that list sounds like a lot, the xDuoo MT-02 is an easier start. It takes ordinary RCA inputs and still offers a 4.4mm jack.
Sound and Headphone Pairing
A balanced Class A hybrid is built for control with a touch of tube warmth. Expect a clean, spacious presentation with a little smoothness from the tubes. The matched 12AU7 pair gives you a tuning option. Apos says 6922 tubes can add depth and detail, so tube rolling is part of the appeal.
Power is the practical advantage. The Gremlin is rated at 1,250mW into 32 ohms and works with 8 to 600 ohm headphones. That is far more than the 300mW of the Fosi Audio GR70. It handles most dynamic headphones and many planars. Even so, the very hardest planars may still want a bigger amp.
Sensitive IEMs are a weaker match. A high-power tube hybrid leaves little room for a quiet background. For IEMs, an amp like the FiiO K5 Pro ESS is a better choice.
Setup, Tubes and Heat
Setup is easy once the balanced chain is in place. Connect your balanced source to the XLR or 4.4mm input. Plug in the included 18 to 24V DC adapter. Then connect your headphones, and let the tubes warm up for a few minutes.
The Gremlin is a Class A design with tubes, so it runs warm. Owners report that it benefits from airflow. Give it space on the desk and do not stack things on top of it. Tubes wear over time and can be replaced, and Apos offers a one-year warranty.
Apos Gremlin vs the Alternatives
Versus the xDuoo MT-02: the MT-02 is easier to fit into a system. It takes RCA inputs and still offers a 4.4mm balanced jack. It also has a pre-out. However, the Gremlin is the more serious balanced design with the higher power rating.
Versus the Fosi Audio GR70: the GR70 is single-ended, with RCA inputs and tone controls. It is the easier plug-in for an ordinary setup. The Gremlin has far more power.
Versus the Douk Audio E2: the E2 offers XLR and 4.4mm jacks without a truly balanced circuit. The Gremlin is balanced from input to output. The E2 has RCA inputs and a VU meter.
Versus a solid-state amp: for IEMs and the quietest background, choose from our best headphone amplifier under $200 list. For a solid-state alternative, see our Topping L30 II review.
Verdict: Is the Apos Gremlin Worth Buying?
Yes, if you have or plan to buy a balanced source. The Gremlin offers a balanced Class A path, strong power and replaceable tubes at a price that normally buys much less. As a result, it is a better fit for enthusiasts than for casual listeners.
It is not the amp for RCA-only setups or for sensitive IEMs. For the wider field, see our best tube headphone amplifiers under $250 roundup.
- Class A and fully-balanced at an unheard of price The Gremlin Class A Tube Headphone Amplifier is a little monster with a ferocious bite. With 1250mW of output power, it has the muscle to drive most headphones that cross its path. It may be ugly, naked, and small, but don't judge a beast by its cover. For just $135, you're getting a Class A, fully-balanced headphone tube amplifier with matched tubes—something unheard of at this price. It delivers sound that’s sumptuous and lush, with musical tonality and heart-melting mids. Once it gets its claws in you, you won't want it to let go.
- Feeding the beast: Tubes + transistors The Gremlin is a hybrid headphone amp that combines the precision of transistors with the warmth of vacuum tubes. While solid-state amps (which rely solely on transistors) deliver accuracy, they lack the soul of tubes. In the Gremlin, the vacuum tubes in the pre-amp stage flood your music with rich harmonics and a warmth that solid-state amps can’t touch.
- A poised predator: a fully-balanced amplifier With a fully-balanced design featuring balanced XLR inputs and balanced 4-pin XLR / balanced 4.4mm outputs, the Gremlin cancels out the kind of hums, buzzes, and interference that can creep in with unbalanced systems. This means you get a cleaner sound—especially important if you're using sensitive headphones or high-end equipment that picks up every little detail. The Gremlin gives you the best of both worlds: the warm, rich tones of tube amplification with the minimal interference of balanced design.
- Matched Ray Tubes: the Gremlin’s natural weapon The Gremlin comes armed with a matched pair of CORE 12AU7 tubes from Ray Tubes to give you that signature tube warmth right out of the box. When tubes are matched, it means they’ve been carefully tested to ensure they work together as a pair, delivering the same output and frequency response. This results in better soundstage, clarity, and stereo imaging—key elements for an hi-fi listening experience.
- Embark on the quest for your perfect sound The Gremlin Amp is made for audio lovers who want to explore the world of sound. It works with any 12AU7 or 6922 tubes, new or old, allowing you to easily swap and try new types. Whether you prefer a lush or linear sound, the Gremlin lets you customize your audio setup whenever you want a change.
Apos Gremlin FAQ
Does the Apos Gremlin have RCA inputs?
No. The Gremlin takes balanced XLR and 4.4mm inputs only, so it pairs most naturally with a DAC or source that has balanced outputs. With a single-ended source you will need a suitable adapter cable.
Does the Apos Gremlin have a built-in DAC?
No DAC is listed in the specifications. It is a headphone amplifier, so you feed it from a separate DAC or any balanced-output source.
What tubes does the Apos Gremlin use?
It ships with a matched pair of 12AU7 tubes and is designed for 12AU7 or 6922 types. Apos says the 6922 can add depth and detail, so those are the tubes to look at if you want to experiment.
Can the Apos Gremlin drive high-impedance headphones?
Apos rates it for headphones from 8 to 600 ohms with 1,250mW at 32 ohms. That covers most dynamic headphones and many planars, though the biggest, least efficient planars are better matched with a higher-power amp.
Does the Apos Gremlin get hot?
It is a Class A design with tubes, so it runs warm. Owners report that it benefits from airflow, so give it space on the desk and do not stack things on top of it.
