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Rogue Audio Sphinx Integrated Amplifier Repair

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!

Rogue Audio Sphinx
Nice toroidal transformer, this turned out to be the culprit, primary winding was open.
Rogue Audio Sphinx
Board quality and layout are both very good
Rogue Audio Sphinx
Tube preamplifier section, excellent board layout evident here
Rogue Audio Sphinx
The two Hypex switching output modules
Rogue Audio Sphinx
Overall view of layout and chassis. Plenty of room and the parts layout again is generous. Premium wiring is used throughout the amplifier. It’s probably let down by the Hypex modules in reality, sounding typically lean and ‘thin’ due to the class-D amplifier modules.
Rogue Audio Sphinx
All of these points must be desoldered and the wires pulled
Rogue Audio Sphinx
Job done…
Rogue Audio Sphinx
New transformer, direct from the USA, complete with new mounting washers and top plate
Rogue Audio Sphinx
And here, soldered into place and wire-tied as per factory specs. This looks completely standard, no way to tell I replaced the transformer.
Rogue Audio Sphinx
Finished amplifier, ready for her owner to enjoy her once again!

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