Cayin RU9: Pocket-sized Nutube 6P1 Vacuum Tube Dongle
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The Evolution of RU Series
In the realm of portable audio, Cayin has consistently pushed the boundaries of innovation, crafting devices that blend cutting-edge technology with exceptional sound quality. Our journey through the RU series exemplifies this commitment, as each model features a unique architecture.Cayin RU6: The Pioneer of Portable R-2R
Launched in 2021, the Cayin RU6 was a game-changer—the first to bring R-2R technology into the dongle world.Before RU6, R-2R DACs were synonymous with bulky equipment, packed with massive circuit boards and countless resistors. The idea of shrinking such a complex architecture into something that fits in your pocket? Unthinkable.
But we took on the challenge. With an in-house developed 24-bit discrete R-2R resistor ladder circuit, the RU6 delivered the beloved R-2R sound signature in a form factor no one had seen before. It supported PCM up to 384kHz, maintained separate digital and analog circuit boards to minimize interference, and featured both 3.5mm single-ended and 4.4mm balanced outputs—all while staying compact enough to slip into your pocket.
What was once a massive setup is now something you can carry anywhere.
Cayin RU7: Advancing to 1-Bit Technology
Building on the R-2R revolution of the RU6, Cayin took another bold step in 2023—this time, embracing 1-bit DAC architecture with the RU7.
Inspired by our flagship N7 DAP, the RU7 featured a fully balanced discrete 1-bit resistor networks, meticulously crafted with 128 high-precision thin-film resistors. The RU7 supported native DSD decoding and featured an "All-to-DSD" processing approach, converting all digital audio signals to DSD format before playback. With the RU7, Cayin brought the allure of true 1-bit DSD audio into the palm of your hand.
Cayin RU9: Our Most Compact Nutube 6P1 Application Ever
Now in 2025, Cayin continued its tradition of innovation with the RU9, introducing the Nutube 6P1 vacuum tube into the portable DAC/Amp, or to say, dongle landscape. This integration aimed to provide the musicality of Nutube 6P1 tube, all within a pocket-sized device.
The progression from the RU6 to the RU9 showcases a relentless pursuit of audio perfection. Each model introduced groundbreaking technologies:
- RU6: First ever discrete R-2R ladder application on dongle
- RU7: First ever 1-bit architecture application on dongle
- RU9: First to apply Nutube 6P1 on dongle
This is our dedication to innovation—to constantly bringing you something different, something that challenges conventions and redefines what’s possible in portable audio.
And the RU9 is currently in the Engineering Prototyping stage, the final technical specifications and functions are still being refined. That means everything we’ve shared today is subject to change as we continue to fine-tune it.
For those eager to experience it firsthand or know more about it, RU9 will be showcased at Shanghai Expo (March 1 – March 2, 2025) and the upcoming CanJam Singapore—see you there!
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Ben86
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What dac chip it use?
Younghunko
New Head-Fier
DAC/AMPs without an SD card slot are extremely inconvenient.
Models like the Onix XP1, HIFIMAN HM1000, Shanling H5, and H7 all include this feature.
Does this device support an SD card?
I believe that an SD card slot is an essential feature for portable DAC/AMPs.
Models like the Onix XP1, HIFIMAN HM1000, Shanling H5, and H7 all include this feature.
Does this device support an SD card?
I believe that an SD card slot is an essential feature for portable DAC/AMPs.
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Even though it is much larger than most dongles, I think they are intentionally using the "dongle" term to indicate that it requires pairing with a source for playback rather than being able to act as a source on its own.
Otherwise is would be called a DAP. 
Yep, used DAC would be interesting or planed DAC.
Yep, used DAC would be interesting or planed DAC.
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lol, yup.Otherwise is would be called a DAP.
The usual questions remain and perhaps we will get some of those answered via feedback from this weekend's show - DAC chip and format compatability, rated power output for SE and BAL, battery life, tube suspension design, amplification mode options, estimated price target, estimated release date, etc. I like the inclusion of a volume knob vs buttons and what appears to be magnetic attachment support for use with phone sources.
originalsnuffy
Headphoneus Supremus
Almost all "tube" portables are really hybrid. It would be great to know about where the tube is applied in the sound chain. Also, as already noted, what is the underlying DAC? The RU7 is already pretty great so it would be nice if they could top that.
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RU9 is a nice portable thing, sounds nice, but runs pretty hot! I’m trying it now, at SH.
AnamCeoil
100+ Head-Fier
Great to see this, and the RU7 is just a fantastic piece of kit.The Evolution of RU Series
In the realm of portable audio, Cayin has consistently pushed the boundaries of innovation, crafting devices that blend cutting-edge technology with exceptional sound quality. Our journey through the RU series exemplifies this commitment, as each model features a unique architecture.
Cayin RU6: The Pioneer of Portable R-2R
Launched in 2021, the Cayin RU6 was a game-changer—the first to bring R-2R technology into the dongle world.
Before RU6, R-2R DACs were synonymous with bulky equipment, packed with massive circuit boards and countless resistors. The idea of shrinking such a complex architecture into something that fits in your pocket? Unthinkable.
But we took on the challenge. With an in-house developed 24-bit discrete R-2R resistor ladder circuit, the RU6 delivered the beloved R-2R sound signature in a form factor no one had seen before. It supported PCM up to 384kHz, maintained separate digital and analog circuit boards to minimize interference, and featured both 3.5mm single-ended and 4.4mm balanced outputs—all while staying compact enough to slip into your pocket.
What was once a massive setup is now something you can carry anywhere.
Cayin RU7: Advancing to 1-Bit Technology
Building on the R-2R revolution of the RU6, Cayin took another bold step in 2023—this time, embracing 1-bit DAC architecture with the RU7.
Inspired by our flagship N7 DAP, the RU7 featured a fully balanced discrete 1-bit resistor networks, meticulously crafted with 128 high-precision thin-film resistors. The RU7 supported native DSD decoding and featured an "All-to-DSD" processing approach, converting all digital audio signals to DSD format before playback. With the RU7, Cayin brought the allure of true 1-bit DSD audio into the palm of your hand.
Cayin RU9: Our Most Compact Nutube 6P1 Application Ever
Now in 2025, Cayin continued its tradition of innovation with the RU9, introducing the Nutube 6P1 vacuum tube into the portable DAC/Amp, or to say, dongle landscape. This integration aimed to provide the musicality of Nutube 6P1 tube, all within a pocket-sized device.
The progression from the RU6 to the RU9 showcases a relentless pursuit of audio perfection. Each model introduced groundbreaking technologies:
- RU6: First ever discrete R-2R ladder application on dongle
- RU7: First ever 1-bit architecture application on dongle
- RU9: First to apply Nutube 6P1 on dongle
This is our dedication to innovation—to constantly bringing you something different, something that challenges conventions and redefines what’s possible in portable audio.
And the RU9 is currently in the Engineering Prototyping stage, the final technical specifications and functions are still being refined. That means everything we’ve shared today is subject to change as we continue to fine-tune it.
For those eager to experience it firsthand or know more about it, RU9 will be showcased at Shanghai Expo (March 1 – March 2, 2025) and the upcoming CanJam Singapore—see you there!
Curious as to whether an RU8 is/was ever contemplated? Seems an odd omission, unless I am the one missing something?
mrcmaj7
New Head-Fier
I want this and I hope black is a color option.
audionewbi
Headphoneus Supremus
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If cayin is able to capture the sound of N8 without the dap functionality, it is a massive win for original N8 lovers.
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