I recently repaired this Rogue Audio Sphinx hybrid valve / class-D integrated amplifier. The repair also reminded me of a valuable lesson in always checking the obvious!

The Rogue Audio Sphinx is a nicely made amplifier, hand-built in the USA which is a good thing. The amplifier features an unusual topology, consisting of a tube preamplifier, solid-state power supply, support circuitry and two Hypex class-D output amplifier modules. My customer brought this Rogue Audio Sphinx to me, complaining that it went dead during use. I spent some time diagnosing the fault and proved to myself once again, why it’s critical to always check the basics.

At first, I could get nothing happening at all. No rails, no voltages anywhere. All the obvious things tested good – switches, fuses, wiring. Well, not ALL the obvious things. It has such a lovely transformer that I didn’t initially consider that it might be dead. A quick test and sure enough, the primary was open. Could be a blown thermal fuse or just an open primary, either way, it’s dead!

A quick conversation with Rogue Audio in the USA saw a new transformer on its way to Australia. I pulled the old one, soldered in the new one and she was good to go!