Un-improving a Jadis · Decades of Musings on HiFi

This pair of Jadis amplifiers arrived on my bench in the late noughties, with a history.

What was wrong

The amplifiers had blown up completely: bad mains, valve runaway and smoke. The output transformers and the circuits were destroyed, in both channels. Big time.

A Hong Kong “Shifu” (Shifu = Master) was then given the job. Rather than repair or rebuild the amplifiers, he redesigned and “improved” them. They did get new output transformers, which I rate as better than Jadis’s own. But the circuit he used was neither well thought out nor well optimised.

The owner was extremely dissatisfied. He wanted his amplifiers “re-Jadis’ed”, and had not turned his system on for over a year.

Photograph: an amplifier’s top plate with a black transformer case labelled Tango, two large blue capacitors, a chrome-covered transformer and corrosion marks on the plate — As it arrived: a Tango transformer, two large blue capacitors and corrosion on the top plate.

Photograph: the underside of one amplifier, chassis on end, with white wirewound resistors, brown electrolytic capacitors and wiring above the green circuit board — As it arrived, under the chassis.

What was done

The job started with electronic archaeology: finding a documented, reliable schematic, and finding pictures of the internals to establish which parts Jadis had used.

No original JA-30 schematic could be located. The JA-80 schematic served as the guide instead: it is the same circuit, but with double the output valves.

Photograph: an amplifier on the bench with its valves fitted, a printed schematic headed Jadis JA-80 in front of it, and boxed new valves from Mullard and Tungsram beside it — The JA-80 schematic, used as the guide, and a set of boxed valves.

Rebuilding the amplifiers to the original design was then actually the easy part.

Photograph: an amplifier chassis standing on end, opened, with most of the wiring removed — Stripped.

Photograph: the copper side of a green circuit board, marked Jadis 44 in script — The main board, marked \"Jadis 44\".

Photograph: parts laid out on a dark foam mat: four large blue capacitors, a row of smaller electrolytic capacitors, and a pile of resistors, wire and a small board — What came out: the four blue capacitors, smaller electrolytics, resistors and wiring.

Result

Photograph: the underside of a rebuilt amplifier: valve sockets, grey wirewound resistors, black MCap and yellow Rel-Cap film capacitors and gold-sleeved electrolytic capacitors, neatly wired — Rebuilt, under the chassis.

Photograph: the two finished amplifiers side by side on the bench, each with a chrome-covered transformer, a black Tango transformer case and its valves fitted — The finished pair. The Tango transformers stayed.

I personally did not like the result all that much. The owner, however, was greatly satisfied: his amplifiers again gave the “good sound” he had come to be accustomed to.

And arguably, in his own classic “Hong Kong” system, the sound of the whole was excellent: BBC LS3/5a loudspeakers with bass extenders, a Jadis preamplifier, an early-1990s DAC whose make I no longer remember, and a CEC belt-drive CD transport.

Photograph: the two amplifiers side by side on a low stand in the owner’s room, with power cords connected and power lights on — Back home, in the owner's system.