Sparkos Gemini Tube Headphone Amplifier – HiFi Delight Meets American Precision
Sparkos Gemini is a $995 USD Tube Headphone Amplifier with RCA inputs, RCA outputs, XLR Headphone outputs, and with Sparkos Labs SS2590 Discrete OPA Output Stage. Today we will review the Sparkos Gemini and compare it with other headphone amplifiers we recently reviewed, including Aune S17 PRO (699 USD), Feliks Echo 2 (799 USD), and Violectric HPA V340 (2000 USD).
Introduction
Sparkos is a popular company from the USA, best known for having an all-USA production of their equipment. Based in Colorado, Sparkos makes both headphone amplifiers, and Op-AMPs that you can use in other products, with Mr. Andrew Sparkos as the leading engineer developing the circuits used in all the Sparkos Products. With a love for dogs and an approach based on measurements and engineering, Sparkos makes products that are reliable and generally well-received, having been in business for a long time now, and having survived the test of time. As an Amazon Influencer, I earn from qualifying purchases, and using the purchase links in my reviews helps me maintain this website and Youtube Channel. Huge thanks to Sparkos Labs Inc. for providing us with the sample for this review.
PROs – Deep and powerful sound, with multiple ways to fine tune it. Multiple gain levels allow the Gemini to have both a granular volume control for IEMs, but also a high driving power for hard-to-drive planar magnetic headphones, being able to even drive the HIFIMAN Susvara. Reliable circuit design and one of the most beautiful and documented circuits I’ve seen in my entire life. You can add or remove the tube influence or set the bias to high or low.
Cons – Needs a source with a low noise level, otherwise it easily inherits the noise from the RCA input.
Product Link
Official Link – https://sparkoslabs.com/gemini-headphone-amp/
Build Quality/Aesthetics
Sparkos Gemini is a high-end Headphone Amplifier with two headphone outputs, both in 1/4 Inch and 4-Pin XLR formats. I am absolutely in love with the level of transparency shown on the main web page of the Gemini, as I am able to easily find everything about the amp, including the power output, and a good selection of the important inner components.
Starting with the face of the amplifier, we have an on/off switch, an LED to show when the Gemini is working, and the two headphone outputs. Inside the unit there is an input attenuator that can apply a -15dB strength, and the whole AMP has a 40 Second Tube Warm-Up Delay. The amount of Tube Sound is user controllable, and we have 6922 Vacuum Tube Front-End, with no capacitors in the signal path, and with zero global feedback.
At the heart of the AMP, we have Sparkos Labs SS2590 Discrete OPA Output Stage OP-AMPs, and the volume control is an Alps Blue Velvet Volume control. There are RCA PreAmp outputs at the back of the Gemini, and it has a high damping factor, providing a gain of 12 dB in low gain, or 21.5dB in high gain. The Unloaded Crosstalk between channels is around 100dB, while the Power Output for a 32 OHMs impedance is 2 Watts, and the power output for a 300 OHM Impedance is 750 mW. This rounds up to a 15V Peak Output voltage, and the THD varies between 0.1% and 1.5% depending on settings.
We have multiple ways of fine tuning the sound, including tube rolling, as Gemini uses versatile ECC88 or 6922 Dual Triode Tube. You can configure both how much Tube character is drawn in the AMP, but also how much bias the tube should have, with the default setting being the sweet spot for the tubes installed. As the Tube is on the Front End, sound passes through it right after it passes through the Alps Blue Velvet Volume Control, acting a bit like a PRE Tube. The current from the tube is extracted from the tube using Current Mirrors rather than coupling capacitors, and then the signal is applied to the SS2590 Discrete Op-AMP, for driving the headphone and RCA outputs. The Gain button allows you to control how hard the tube is driven, and how much Tube Character is infused in the sound.
Pressing on the Gain button means having more Tube Character, and an attenuation of 10 dB, while disengaging it means having 10 more dB and less tube character. Sparkos Labs Inc also believes strongly in not using any kind of capacitors, so Gemini has zero capacitors. While coupling capacitors are typically used to block the large DC voltages that exist on the tube plates and the cathode, when designing the Gemini, Sparkos Labs Inc used a different approach and employed a novel cascode Wilson current mirror to couple the audio signal out of the tube. After this step, we have a DC servo to strip off the bias current and leave only the audio signal. There is no need to think about what kind of capacitor or capacity is used for the Gemini, as there is none used.
There is no Global Feedback, so that you can hear as much of the Tube Sonic character as possible. The Alps Blue Velvet Volume control has perfect channel balance starting with 8 o’clock, one of the best I have heard, and even theoretically, it has one of the lowest distortions possible in the audio world. This is one of the best high-end volume potentiometers commercially available, and one of the most widely used controllers in high-end audio. To access the Tube Bias Current or to get even more fine tuning for how much tube character gets mixed in the signal, there is a jumper inside the Gemini, and you can easily configure it for high bias, or to get less tube character in the sound. Gemini comes out of the factory with the jumper set to low, which means that more tube character gets mixed in the sound.
Subjective Usage
I have experimented quite a bit with the Gemini, including taking off the metallic hood and playing around with taking out the jumper and setting the Bias to high Bias, or setting the tube influence to a lower level. I have to say that Gemini has one of the most beautiful and carefully designed circuits, it is beautifully clean, descriptive, and makes you know that Mr. Andrew Sparkos loves working on designing those amplifiers, and giving his best when selecting the inner components. Everything is pure high-end, and my only recommendation for taking the unit apart is testing whether you prefer setting the bias to high, or having less tube character.
It is much harder to explain what Tube bias is, but I prefer high bias all the time when I can select it, as although it lowers the number of harmonics a bit, it also lowers the THD and increases the clarity of the amplifier significantly. If my understanding of the circuit board is correct, there will not be a difference between the XLR and the RCA outputs, and the two are included so that you can use your favorite cable, but the two should be equal, all things considered.
You cannot replace the default SS2590 Op-AMps, which are single by design, but you can order those from Sparkos for other amplifiers, if you like the sound. Even more intriguing, when turning the AMP on and Off, you can get a bit of a pop sound, if the bias is set to low, but that does not happen if the bias is set to high, which coincides with how the tubes work. Overall, the unit has no EMI or RFI, and the outer shell has a frosted metal design, which is not a direct indicator of how tidy the inner circuit is.
Gemini has more than plenty of power for the hardest to drive headphones I have in my collection, including HIFIMAN Susvara and Dan Clark Expanse, but it can also work really well with IEMs, showing zero hissing and background noise even with my most sensitive IEMs, including Campfire Ara, Campfire Moon Rover and Sweear He-Live5. Oddly enough, although it is not the most sensitive IEM, Ie900 has a bit of background noise that increases with volume, but I seem to only notice the effect with Ie900 in particular.
Sound Quality
Pairings – While there is no general reason to put the Gemini so much to the test, there is no real good reason to not do it either, so for this review I mainly used HIFIMAN Susvara, HE1000SE, and Susvara Unveiled as hard to drive headphones, but also DCA Dan Clark Expanse, and Erzetich Mania V2024. For easier to drive, but still fun to listen to headphones, I have paired the Gemini with Palma DHS-1, Crosszone CZ-8a Enhanced, T+A Solitaire P-SE, and Erzetich Thalia. For the IEM list, I have paired the Gemini with Sennheiser Ie900, Campfire Moon rover, Campfire Bonneville, Spirit Torino Twin Pulse Beryllium, NF Audio NE4, RAPTGO LEAF D01, Soundz Avant and Soundz Flame. For all my tests, I have used the XLR output, with a ddHiFi XLR44B in between to make the connection happen.
For hard to drive headphones, Gemini has plenty of power, and a detailed, crisp sound, with excellent control and power, a laid-back and somewhat dark-ish sound, plenty and powerful bass, and outstanding precision. For IEMs, I am hearing an even better precision and detail, but an increase in the noise floor, with a much higher noise floor if you disengage the gain button, so basically if you go for the extra 10dB, they will increase the noise floor too, with IEMs. I would be tempted to say that this indicates Gemini works well for the middle part, as it sounds beautiful with Palma DHS-1, but in reality it pairs beautifully with all the IEMs and Headphones I paired with it. As my main DACs have been HIFIMAN EF400, Dethonray Listening M1, and Musician Pegasus II R2R DAC, I noticed that with both IEMs and Headphones, I prefer the sound of the Gemini over that of high-end DAC/AMPs, and at many times, it is worthy to add the Gemini on top of the Listening M1, even though Listening M1 is the DAC in that setup. I prefer the dynamics, depth and power of the Gemini, and the character it has.
Overall Signature – Although it will feel a bit hypocritical, the combination I like the sound of the Gemini most is not the default one, and I prefer the sound when using high bias, so it will be the way I am describing the sound of the Gemini. There is no difference between using the volume gain and a DAC with volume, because the volume is directly the first step applied to the signal of the Gemini. This also means that it generally has a perfect volume control and the best sonic performance at all volume levels, which makes it exceptionally versatile for a wide selection of IEMs and Headphones. Using more tube character, or leaving the bias at low bias, will make the sound more textured and draw in more character from the tube, and setting the bias to high will make the sound tighter, darker, more precise, but also bring in a bit less tube character and associated distortion. Gemini generally sounds detailed, crisp and revealing, with peaking dynamics, and an engaging signature. There’s a bit of tube character always present in the sound, and the signature has a preference towards a full and deep bass, highlighting the bottom end. You always hear that high damping factor, but we will explore it down below.
Bass – We start with one of the deepest, most powerful, controlled and earth-shattering low-end rumble levels heard in an amplifier around this price point. Bass on the Gemini is deep, powerful, lush, and that high damping factor makes it buttery smooth, clean and controlled, both with hard to drive headphones and IEMs. We get an excellent extension, down to 20 hz, and many IEMs and Headphones that tend to have a bit of roll-off in general will sound full, deep and lush with Gemini. The bass is entirely enhanced, from the sub all the way to the mid bass, and even with a bit of extra weight and presence in the upper bass, although it does not introduce veil or force its presence on the midrange.
Midrange – Gemini sounds detailed, dynamic and revealing in the midrange. As it has a high damping factor, textures and instruments, voices and instruments are generally lush and smooth, clean and free of grain. This pairs well with having a tube pre, but I still prefer taking this to the extreme and setting the bias high, which makes the sound the smoothest, deepest and even slightly dark in tuning. You can change this with different tubes, and that’s a big part of the Gemini beauty, you can fine tune it heavily, but taking it to the max smoothness and precision you get a really detailed sound that’s engaging yet dynamic and colorful. There is a bit of dark coloration added to the midrange, and that’s because the treble up above is smooth and laid-back, slightly recessed, but the bass is also enhanced and powerful, so the effect is twofold. Both male and female voices are rendered beautifully, with excellent presence and tonality for both, but this also means guitars, pianos and violins sound beautifully.
Treble – Gemini is all about the smoothness and relaxation, at least using the default tube, so you can expect a sound that is free from fatigue, free from distortion, but which is lush and laid-back. The treble extension goes as high as 18 kHz audibly, but it rolls off in presence and strength starting with 9 kHz, with a progressively stronger roll-off effect. This, entwined with the high damping factor, creates a silky smooth treble that’s easy on the ears and enjoyable even with headphones and IEMS that are known to be harsh and bright. Gemini makes a beautiful pairing with HIFIMAN’s brighter models too, like Arya Organic, but it can be a bit too laid back and relaxed for models that are already as such, like Aune Audio SR7000.
Loudness Saturation Gradient – Thanks to multiple implementations and the design, Gemini has zero variation of clarity, resolution with volume, and it behaves the same at the extremes as it does in the middle, sounding perfectly cohesive and consistent regardless of how hard or easy to drive the IEMs / headphones connected to it are, and what kind of volume you’re pumping into them. As the volume potentiometer will change the input signal, you can expect exactly the same signature and tuning across all volume levels. If anything, I noticed that with IE900 in particular I can hear the noise floor increasing with the volume, and that engaging the gain button has a higher noise floor. This being said, from my understanding this is caused by the source dac noise, because that gain is a dampener on the input gain and will in-mix or out-mix some of the tube, but the THD is lower when tube is gained in, and not out, so self-gain on the Gemini is very low. In fact, regardless of what I am running, if there is no DAC, the effect of the hissing with IEMs disappears, so there may be certain DACs out there or cables that can do a bit better in this aspect.
Dynamics Handling – Gemini sounds surprisingly dynamic and engaging, creating punch and contrast really well. Despite a lower amount of upper treble / harshness / grain, it can reveal detail and sound very dynamic. There is no limitation in its tuning and signature, as Gemini is one of the most enjoyable Headphone AMPs you can grab around the price point.
PRaT / Textures – Textures are always smooth, lean and relaxed with the Gemini, thanks to its high damping factor. Staring with this smooth and lush presentation, you can add more texture, especially desirable harmonics by employing more tube character or different tubes, which is a very fun way to allow the user to mix and fine tune their sound.
Soundstage – Gemini sounds natural in the soundstage. It has a strong imaging and stereo separation, with very good layering, but it will present a soundstage that is best described as natural, it extends nicely in the width and depth, but only does so when the song asks for it. Usually, you can fine tune even this behavior with different tubes, as some can sound more intimate and some more holographic, the default one being a good middle ground.
Comparisons
Sparkos Gemini vs Feliks Echo 2 (995 USD vs 799 USD) – Feliks Echo 2 is an OTL AMP, which comes with many differences, both advantages and disadvantages. While both amplifiers need a high-quality DAC and both mainly take in an RCA single Ended signal, Echo 2 is less sensitive to source noise, but it can mainly drive the middle ground, having a lower driving power at maximum, and being less capable of driving hard to drive planar magnetic headphones, but it also does not handle IEMs well, as there is too much for them from the OTL design. This means that while you can use Gemini for headphones like DCA Expanse and IEMs like Campfire Moon Rover, you can use Echo 2 for high-impedance headphones like Sennheiser HD 480 PRO Plus, or Palma DHS-1. The sonic character of the two is quite different too, with Echo 2 sounding brighter, sharper and more neutral in the bass, while Gemini sounds much fuller, deeper, darker and has much less treble, more bass, a heavier sound and a much higher damping factor, with potentially more and less tube character, whereas Echo 2 has a bit less tube character in general, and a lower THD in general. Both amplifiers are great, but if you have a wider selection of headphones and IEMs, Gemini is a more versatile option, while if you have a few headphones which are either high impedance, or not very hard to drive, Echo 2 is excellent too, especially if you’re looking for a neutral, clean sound with very little deviation and coloration.
Sparkos Gemini vs Violectric HPA V340 (995 USD vs 2000 USD) – V340 has been launched a while ago, but it still is relevant, and has one of the most solid designs out there. It is a fully solid-state Headphone AMp / Pre, with a full balanced design, while Gemini is a single ended AMP, with RCA inputs and outputs. HPA V340 also has only RCA inputs, so it has a similar noise floor when compared to Gemini. Although both have a high driving power, Gemini actually handles HIFIMAN Susvara, and DCA Dan Clark Audio expanse better, with more bass, better control and less distortion at high volumes, and with a lower noise floor at lower volumes for IEMs. HPA V340 is theoretically better for high-impedance headphones, as it has a 50V internal voltage, and it has a 5W peak power at 50 OHMs of impedance, with 21V RMS at 600 OHMs, more than perfect for those high-impedance headphones, while with Gemini you can experiment a bit with the sound. Both amplifiers having a high damping factor, and both have a smoother texture, but the main signature is much much brighter, sharper and more easily fatiguing with HPA V340, and more relaxed, laid-back and smoother with Gemini, which sounds full, deep, lush and powerful. There is more bass, and a darker sound with Gemini, and a more airy sound with HPA V340. The soundstage expands wider with HPA V340, but it is deeper for the Gemini.
Sparkos Gemini vs Aune S17 Pro (995 USD vs 699 USD) – In theory, S17 Pro is the most similar AMP sonically to the Gemini, but there is a huge difference in the design, as S17 PRO is a Class A AMP that runs quite hot, while Gemini barely gets warm outside of the tube which gets hot, but not extremely so. S17 PRO has a much higher maximum output power, up to 7.5W, and it has a fully balanced design, while Gemini can still drive most headphones that S17 PRO can, without any inherent disadvantage. S17 PRO can work with a remote, and it has multiple current levels, while Gemini has multiple gain levels, multiple bias levels and does not have a remote, and it has an analog volume controller. In practice, the sound of the two is fairly similar, both Gemini and S17 PRO have a darker, fuller sound with a high damping factor, but Gemini sounds a bit more engaging, more colorful and has more midrange color, even if you set the tube gain and presence to minimum and bias to high, it still will have more character and tube charm, while S17 PRO will always sound more relaxed, laid back and smoother, but Gemini actually has the upper hand in the impact, punch and bass dynamics. Both are excellent choices, I would pick Gemini to experiment and hear the tube magic, and S17 PRO for a solid state option with higher driving power.
Value and Conclusion
Although Gemini does not have a low price, it is an amplifier with one of the tidiest, most beautiful circuit designs, assembled and made in the USA with only USA-Sourced components, being a true marvel of engineering, and having a beautiful sound that can improve your experience even if you’re running high-end DAC/AMPs already.
Before the end of today’s review, Gemini does deliver a signature and sound so good that I will be adding it to the Audiophile-Heaven Hall Of Fame, it is impressive, no matter what way you look at it, with the fullest, deepest bass you can achieve around the price point, and with a high damping factor that makes all music lush and smooth, grain-free and enjoyable.
At the end of today’s review, if you’re looking for an excellent headphone amplifier / preamplifier with a tube pre stage, and with a consistent volume control, and both enough power for even the hardest to drive Planar Magnetic Headphone, but still control and low noise for IEMs, and if you want it to be made in the USA with multiple ways to fine tune it, Sparkos Gemini is a top choice I can fully recommend you today.
Product Link
Official Link – https://sparkoslabs.com/gemini-headphone-amp/
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Full Playlist used for this review
We listened to more songs than those named in this playlist, but those are excellent for identifying a sonic signature. I recommend trying most of the songs from this playlist, especially if you’re searching for new music! The playlists are different for Spotify, Tidal and Youtube, and based on the songs I enjoy and are available on each!
https://www.youtube.com/playlist?list=PL_cjBXGmwSHSdGcwuc_bKbBDGHL4QvYBu
https://open.spotify.com/playlist/5J3oloz8Riy9LxEGenOjQ0?si=979ba4f082414be7
https://tidal.com/browse/playlist/330fd544-8e5b-4839-bd35-676b2edbb3d5
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