Hi Toni, adding fuse protection to the supply rails is a good idea, but you need to consider what might happen if one of the fuses opens under fault. On some amplifier topologies the offset control cannot function with a single supply rail. So, under a fault condition there is a significant DC offset at the speaker terminals. You can check this by removing each fuse in turn and measuring for DC. As the Musical Fidelity design does not has individual supply rail fuses, I suspect the circuit protection relies on a downstream mains fuse or a thermal trip. The transient currents on the amplifier supply rails can be quite high. So, it is better to use a ceramic fuse that has a higher breaking capacity then a glass fuse. A fuse with a time-lag characteristic will also minimise the risk of annoyance fuse ruptures.
Yes definitely if will blow just a fuse and not both will be a DC offset on the output and will be a huge amount of DC voltage on the speaker output, so that's why I added the speaker protection relay to make sure if detects DC voltage on the output will disconnect the speakers from the amplifier directly.
I never trust those Chinese speaker protection boards. The circuits use low quality relays. Mechanical isolation is always a weak point in a protection design. @@SymbolTech21
Class A amplifiers are much better than any other type of amplifier but they give off a lot of heat meaning they run very hot, and I was warned of getting a Musical FidelIty Amplifier, so I purchased a TECHNICS SU A900 Amplifier which lasted for at least 10 years but the electrolytics have since dried out and the unit has been put into storage along with a state of the art tape deck which no longer works, the Musical Fidelity really need to be used in a well ventilated listening room.
