RCA Inputs
RCA Preamp Outputs
¼” Headphone Output
4 Pin XLR Headphone Output
Alps Blue Velvet Volume Control
Sparkos Labs SS2590 Discrete OPA Output Stage
Sparkos Labs Discrete Voltage Regulators
Zero Global Feedback
No Capacitors In The Signal Path
6922 Vacuum Tube Front-End
Allows For Tube Rolling
User Adjustable Tube Bias point
The Amount Of “Tube Sound” Is User Controllable
Tube Heater Soft Start
40 second Tube Warm-Up Delay
User Gain Control Button
User Selectable Input Attenuator Of -15dB
DC Protection For The Headphone Outputs
Very Low Output Impedance < .25 ohms
High Damping Factor
10Hz – 100KHz Frequency Response
Gain Of 12dB (Low Gain) And 21.5dB (High Gain)
Unloaded Cross Talk >100dB @ 1KHz
Power Out 2 Watts Max @ 32Ohms
Power Out 750mW Max @300 Ohms
15V Peak Output Voltage
250mA Peak Output Current
THD 0.1% - 1.5% Depending On Settings
9” Wide, 6” Deep, 2.5” Tall
120 / 240 VAC Operation
 
 
Customizable Tube Hybrid Design
Vacuum tubes have long been revered in the world of audio for their ability to impart a warm, harmonically-rich sound signature that simply can't be replicated by solid-state components alone. They bring a sense of depth, dimension, and character to your music that goes beyond mere amplification. Whether you're a seasoned tube aficionado, or just beginning your journey into the world of high-fidelity vacuum tube sound, the Gemini is the ultimate tube headphone amplifier platform for exploring, experiencing, and customizing  your very own vacuum tube-based audio experience.
Tube Rolling
The first level of customization that you’ll get with the Gemini, is with tube rolling. Tube rolling is the practice of swapping out and changing the vacuum tube type in an audio system to sculpt and customize the sonic character to one's personal preferences. Each tube type will have its own unique sonic signature, characterized by factors like warmth, clarity, imaging, richness, soundstage, and dynamics. The Gemini allows you to roll nearly a dozen different tube types, ranging from the lush, smooth tones of vintage tubes to the pristine clarity of modern ones.
Sonic customization
The next level of customization, is through the front panel gain button. Each tube type will have its own unique sonic signature, but exactly how much of that sonic signature will be imparted onto the sound will depend on exactly how hard the tube is having to work.  A front panel gain button provides easy, immediate control over how hard the tube has to work, how much gain it has, and how much of its unique sonic signature will come through in your listening experience.
The final level of customization, is control over the amount of current that the tube is biased at. This jumper-based user control will behave similarly to the gain button, but it will do so without actually changing the gain, or the perceived volume level that the user will experience. The amount of bias current doesn’t affect how hard the tube has to work like the gain button does, but rather, it defines for the tube what “work” even means in the first place.
A matrix of possibilities
So, there you have it. The Gemini presents a vast, 3-dimensional matrix of sonic possibilities that exist across 10 different tube types, at 2 different gain levels, and 2 different bias points each. The question now is, how far down that rabbit hole do you want to go? Some of us love nothing more than embarking on such an adventure in our search for sonic perfection, while others of us maybe “Ain’t got time for all that.” If you are the latter, don’t worry, we got you. We already selected the best tube, biased it just right, and leave you with only a simple front panel gain button to tailor your sonic experience.
Design Features
Tube Type.  The Gemini comes with a 6922 dual triode tube, which also goes by the name ECC88. In our opinion, it is the one that we think sounds the best. If you prefer a different tube type or want to experiment with your listening experience, the Gemini can run nearly a dozen different tubes and supports tube rolling.
Design Architecture.  The tube inside the Gemini is in the front end, and will be the first thing that the incoming audio will hit right after passing through the Alps Blue Velvet volume control.  We then extract the audio signal from the tube using current mirrors rather than coupling capacitors, and then apply that signal to some of our world class SS2590 discrete op amps for driving the headphone and RCA outputs.    The amount of tube harmonics imparted into the sound will depend on how hard the tube is driven.  The gain button on the front panel allows user control over this.
No capacitors in the signal path.  At Sparkos Labs, we always say that “the best capacitor, is no capacitor.”  Thus, the Gemini tube headphone amplifier does not have any coupling capacitors in the audio signal path.  This is almost unheard of in tube designs. Coupling capacitors are typically used to block the large DC voltages that exist on the tube plates and the cathode when coupling the audio signal out of the tube.  We took a different approach, and used a novel cascode Wilson current mirror to couple the audio signal out of the tube.  We then made use of a DC servo to strip off the bias current, and leave only the audio signal.   Therefore, there is no need to agonize over the coupling capacitor, its type or value, because it does not exist inside the Gemini.