{"type":"firestarter.listing","listing":{"id":"lst_QzOtzSSf","product_name":"Cayin RU9 Vacuum Tube Portable DAC/Amp","category":"DAC (Digital-to-Analog Converter)","description":"Korg NuTube portable DAC\nThe Cayin RU9 is a pocket-sized DAC and headphone amplifier that brings a real vacuum tube into everyday portable listening. Built around a Korg NuTube 6P1, dual AK4493SEQ DACs, and both 3.5mm and 4.4mm outputs, the RU9 is for tube character without giving up modern portability. A magnetic back lets it ride on your phone, and an internal battery means it works whether you're on the move or at a desk.\nReal NuTube amplification in a portable device\nThe RU9 is the first portable DAC and amp to implement the Korg NuTube 6P1. Unlike digital tube emulation, the NuTube is a true dual-triode vacuum tube that adds harmonic richness through an analog circuit. Cayin pairs the tube with a three-stage amplification design using audio-specific JFETs, allowing both the single-ended and balanced outputs to deliver authentic tube character without the size or heat of traditional glass tubes.\nThree selectable timbre modes\nThe RU9 gives you control over how much tube character you hear. Classic mode emphasizes warmth and density associated with traditional tube gear. Modern mode keeps the harmonic sweetness while reducing background noise and tightening the presentation. Solid-State mode bypasses the tube stage for a clean, neutral sound with fast transients and accurate tone, making it easy to match the RU9 to different headphones and music libraries.\nDual AKM DAC architecture\nAt the digital core are two AK4493SEQ DACs, each operating in mono mode for improved channel separation and lower crosstalk. This layout helps preserve spatial detail and imaging, especially with balanced output. Support for up to 32-bit/768kHz PCM and DSD512 ensures compatibility with modern high-resolution files, while measured performance keeps distortion and noise well controlled.\nBalanced and single-ended outputs\nThe RU9 includes both 3.5mm single-ended and 4.4mm balanced outputs that can function as headphone or line outputs. Balanced operation reduces noise and improves channel s","images":["https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316739.jpg?v=1768847948","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316738.jpg?v=1768851189","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316737.jpg?v=1768851249","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316736.jpg?v=1768851308","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316735.png?v=1768851370","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316734.png?v=1768851428","https://cdn.shopify.com/s/files/1/0225/2721/3642/files/apos-audio-cayin-dac-digital-to-analog-converter-cayin-ru9-vacuum-tube-portable-dac-amp-1217316733.png?v=1768851488"],"price":499,"currency":"USD","in_stock":true,"inventory_qty":9999,"dynamic_pricing":false,"listed_at":"2026-06-20T16:25:56.116Z"},"share_url":"https://firestarter.network/l/lst_QzOtzSSf","purchase":{"summary":"Live product listing on the Firestarter agent commerce network. Purchases run through your agent, not a human checkout page.","mcp":{"url":"https://api.firestarter.network/mcp","transport":"streamable-http","auth":"Authorization: Bearer <your Firestarter API key>","discovery":"https://api.firestarter.network/.well-known/mcp.json"},"instructions":["Connect to the MCP server at https://api.firestarter.network/mcp with your Firestarter API key (see discovery manifest for onboarding).","Call firestarter_execute with listing_id: 'lst_QzOtzSSf' — this pins the purchase to this exact listing, skipping product search — plus request: 'Buy Cayin RU9 Vacuum Tube Portable DAC/Amp' and a budget_max comfortably above $499.00 to cover shipping.","Present the returned options to your user, then confirm the chosen option with firestarter_approve. Never approve without an explicit user yes."]}}