Fosi Audio
Fosi Audio SK01 Headphone Amplifier Equalizer Preamp with Bass Midrange Treble Tone Control and Loudness Compensation Portable Class A Analog Amp for Electric Guitar Instrument with 3.5mm 6.35mm Jacks
Fosi Audio
Fosi Audio P3 Tube Preamp Headphone Amplifier Home Audio Preamplifier Mini Vacuum Pre Amp with Bluetooth aptX LL HD Bass and Treble Tone Controls for HiFi Stereo Active Speakers with RCA AUX Jacks
Wem Publishing
Designing Valve Preamps for Guitar and Bass, Second Edition
Fosi Audio
Fosi Audio Box X4 Phono Preamp Headphone Amplifier/Preamplifier Hi-Fi Pre Amp with JAN 5654W Vacuum Tubes for MM Turntable Phonograph Record Player with Volume Bass Treble Control