Tube Sound: The Monolith Headphone Tube Amplifier utilizes a powerful 6N5P dual triode tube coupled with an output transformer for the output stage. Many competing designs only utilize a large electrolytic capacitor on the output, which degrades sound quality. Dual 6N3 tubes are utilized for the input stage and can cross over to US equivalents 2C51 or 396a. The 6N5P crosses over to a US6080 or 6AS7.ESS Technology: The ESS ES9018 Sabre chip uses the patented 32-bit HyperStream DAC architecture and Time Domain Jitter Eliminator to bring out the best in your digital recordings. The USB receiver is the Savitech SA9227. It supports all sample rates up to 384kHz/32-bit and is clocked by two onboard oscillators.Impedance Selector: Optimize performance for your headphones! The impedance selector allows you to perfectly match the amplifier to the headphone impedance, ensuring that the ideal power is being utilized for any pair of headphones. The impedance can be set to one of five impedance groups, from 16 to 600 ohms.VOLUME: Sets the volume level for your headphones. | INPUT: Selects the Line IN1, Line IN2, or USB inputs. | IMPEDANCE: Match the output impedance to your headphones for optimal sound quality. | HEADPHONES: 1/4" TRS output for headphones, compatible from 16 to 600 ohms.POWER: Powers the amplifier on or off. | LINE IN 1: 3.5mm TRS input for analog audio sources. | LINE 2: Unbalanced stereo RCA inputs for analog sources. | PREOUT: Unbalanced RCA preamplifier outputs that let you utilize the DAC with an external power amplifier. | USB: USB Type-B input connector for connecting your PC or other digital audio source.