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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 very 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 the amplifier 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!

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Nice toroidal transformer, this turned out to be the culprit, primary winding was open.
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Board quality and layout are both very good
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Tube preamplifier section, excellent board layout evident here
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The two Hypex switching output modules
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Overall view of layout and chassis. Plenty of room and parts layout again is generous. Premium wiring is used throughout the amplifier. Its probably let down by the Hypex modules in reality, sounding typically lean and ‘thin’ due to class-D amps.

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All of these points must be desoldered and the wires pulled
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Job done…
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New transformer, direct from the USA, complete with new mounting washers and top plate
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And here, soldered into place and wire-tied as per factory specs. This looks completely standard, no way to tell I replaced the transformer.
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Finished amplifier, ready for her owner to enjoy her once again!

Liquid Mike

As a kid, I cherished my Tandy 200-in-1 electronics project lab, Dick Smith electronics kits, my Dad's hi-fi and my own first proper system. Later, I created Liquid Audio to help keep classic hi-fi gear alive and well. Our mission: to deliver TLC for classic Japanese, American and European hi-fi stereo equipment.

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