The Fab Simple Symetrical Amplifier is meant for higher power than class A USSA series. The goal is to preserve as much as possible the sound signature of the USSA with some differences since it is a class AB (although with medium DC bias). It is similar to the "VSSA-Fab" and "Fab-Four" amps done several years ago but the FSSA is more simple.
My main observation regarding the sound difference between USSA (class A) and FSSA (class AB) Is that USSA is more suitable for jazz, classical, soft rock music and FSSA is better for harder
rock music since bass is tighter. However, it is not too tight that bass becomes thin as for some other amplifiers. FSSA has also medium and high frequencies with a natural feel and soft too.
The topology has similarities with other amplifiers such as the Grand Mos of Solectron but the differences should make it a different sounding amplifier based on my experience.
The FSSA amplifier can deliver up to 120Wrms into 8 ohms in class AB depending on power supply used.
this is a class AB power amp based on USSA-3 class A front end circuit but with follower configuration as output. The bias is relatively high for a clas AB allowing about 3Wrms class A into 8 ohms. The VAS transistor is a Mosfet for Audio type.
this is a class AB power amp based on USSA-3 class A front end circuit but with follower configuration as output. The bias is relatively high for a clas AB allowing about 3Wrms class A into 8 ohms. The VAS transistor is a darlington BJT for Audio type.
The FSSA amp is still a prototype. Stay tuned for pcb availability for diy. The same pcb can be used for both FSSA versions.
Measured THD at 1KHz On one channel of FSSA-1 (2nd harmonic is highest at all these power levels):
1W rms: 0,0014%
4W rms: 0,002%
10W rms: 0,0026%
25W rms: 0,0057%
50W rms: 0,0092%
70W rms: 0,012% (max power before clipping)