{"type":"firestarter.listing","listing":{"id":"lst_NsZIUFEH","product_name":"Cayin C9II Portable Headphone Amplifier","category":null,"description":"Product Highlights\n\n1. Gen5 Nutube 6P1 Vacuum Tube Audio Circuit \n\nCayin has applied this vacuum tube to multiple products, including the N8, C9, N8ii, and N30LE, and now the C9ii. After years of continuous circuit experimentation and technical refinement, Cayin has equipped the C9ii with an adjustable anode (plate) voltage feature and the highly praised Classic and Modern dual tube timbre. This adjustable plate voltage feature offers two levels: high and low.\n\n1.1 Dual Tube Timbre Circuit\n\nModern Sound: Introduces a large-loop negative feedback system, with total gain determined by the large-loop negative feedback circuit. By incorporating negative feedback over multiple amplification stages, the total harmonic distortion (THD) will be reduced significantly. The harmonic distortion characteristics and sound signature lean more toward a modern style, with greatly reduced thermal noise and a slightly cleaner tube sound. The original C9 was designed with a similar NFB circuit. \n\nClassic Sound: No large-loop negative feedback; each stage operates independently through local feedback, with the overall gain determined by the cumulative gain of each stage. The distortion characteristics of the tube amplification circuit dominate the sound signature, resulting in a higher THD value. The distribution of harmonic distortion and the sensor signature exhibit a classic vacuum tube amplification circuit, with relatively more thermal noise and a richer vacuum tube presentation. The N8 DAP was designed with a similar NFB circuit. \n\n1.2 Anode (High/Low) \n\nCayin introduces a new feature, “Anode” to C9ii. The High/Low adjustable anode (plate) voltage further enriches and refines the range of vacuum tube timbre. The working principle is that applying different operating voltages to the plate of the vacuum tube alters its operating state, ultimately affecting the sound signature of the timbre circuit. This mainly manifests in changes in audio linearity, and it will adjust the overlay, ","images":["https://cdn.shopify.com/s/files/1/0031/0453/8673/files/cayin-c9ii-portable-headphone-amplifier-cayin-c9ii-titanium-558190.jpg?v=1764761793","https://cdn.shopify.com/s/files/1/0031/0453/8673/files/cayin-c9ii-portable-headphone-amplifier-cayin-549380.jpg?v=1764761784","https://cdn.shopify.com/s/files/1/0031/0453/8673/files/cayin-c9ii-portable-headphone-amplifier-cayin-964031.jpg?v=1764761791"],"price":2399,"currency":"USD","in_stock":true,"inventory_qty":9999,"dynamic_pricing":false,"listed_at":"2026-06-20T16:26:29.425Z"},"share_url":"https://firestarter.network/l/lst_NsZIUFEH","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_NsZIUFEH' — this pins the purchase to this exact listing, skipping product search — plus request: 'Buy Cayin C9II Portable Headphone Amplifier' and a budget_max comfortably above $2399.00 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."]}}