SFS-80

About the SFS-80

The Sonic Frontiers SFS-80 is a stereo tube power amplifier that delivers 80 watts RMS per channel across the full 20Hz to 20kHz bandwidth. It uses four KT99 (also known as 6550/KT88/KT99) tubes as the primary output tubes, which are high-output tubes suitable for high wattage amplification. The amplifier is built on a design inspired by the Dynaco ST-70 platform but features over-engineered transformers and power supplies to handle the higher power output. It includes a bias meter on the front panel allowing precise bias adjustments of the power tubes, which is appreciated by hobbyists and tinkerers. The frequency response ranges from 6Hz to 50kHz, with an input sensitivity of 0.95V. The SFS-80 is praised for its excellent soundstage, grain-free midrange, and detailed low-level information, making it a favorite for classical and jazz music. However, it may struggle with driving speakers loud on tracks with heavy low-frequency content due to impedance matching issues. The amplifier is known for a warm sound signature compared to Sonic Frontiers' Power series and requires manual transformer reconfiguration to change output impedance between 3.5 and 8 ohms. It is a vintage amplifier from the early 1990s and is no longer manufactured.