A60 protection
Heh - just spotted this.
It is a long time since I designed this but the protection is pretty benign and won't normally get in the way of the music. Leave it alone!
However you could usefully up the fuse value if you like - it probably won't fail under s/c conditions then so try not to short the amplifier under load for more than a few seconds!
The fuse was the main long term s/c protection, backed iup by the electronic protection which would heat up he transistors slowly enough to blow the fuse. The original design was 100% bench tested in the factory by dead shorting each output of every production unit under drive for 5 seconds with the output fuses short circuited. Provided the transistors were properly mounted they wouldn't fail but it sure showed up poor mounting techniques or any barrel shapes in the local heat sink (we called it the heat shunt). The power stages were and still are extremely reliable in the field.
The double slope protection locus calculated above would in my opinion be audible with many loudspeakers and is far too conservative. Part of the art of commercial amplifier design is knowing just where to set the locus! A lot of experience helps 🙂
Sometime I mean to try upgrading the output transistors to modern OnSemi extended beta types - it should work fine.
John Dawson (Arcam)
Heh - just spotted this.
It is a long time since I designed this but the protection is pretty benign and won't normally get in the way of the music. Leave it alone!
However you could usefully up the fuse value if you like - it probably won't fail under s/c conditions then so try not to short the amplifier under load for more than a few seconds!
The fuse was the main long term s/c protection, backed iup by the electronic protection which would heat up he transistors slowly enough to blow the fuse. The original design was 100% bench tested in the factory by dead shorting each output of every production unit under drive for 5 seconds with the output fuses short circuited. Provided the transistors were properly mounted they wouldn't fail but it sure showed up poor mounting techniques or any barrel shapes in the local heat sink (we called it the heat shunt). The power stages were and still are extremely reliable in the field.
The double slope protection locus calculated above would in my opinion be audible with many loudspeakers and is far too conservative. Part of the art of commercial amplifier design is knowing just where to set the locus! A lot of experience helps 🙂
Sometime I mean to try upgrading the output transistors to modern OnSemi extended beta types - it should work fine.
John Dawson (Arcam)
