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Jadis Defy 7

This French made 100 Watt per channel amplifier came in because it kept blowing up valves. It was decided that a major redesign was in order.

(Top Picture) The Jadis Defy 7 in its old guise. Some of the larger componets were simply glued into place, not what one would expect from a 'high end' amplifier.

(Middle Picture) The Jadis is now much simplified, the additional round transformer has been added because the heater windings on the original had gone open circuit, and the speaker impedance adjustment terminals have been done away with as they had broken away.

(Bottom Picture) The completed amplifier has the holes for the now missing valves filled with other components

The main circuit board was stripped of all its components and rebuilt to a far simpler design. As can be seen, over half the parts have been left out, in addition, it now runs only 4 output valves per channel instead of the 6 it originally had and the valves changed from 6550 to KT-120, this was to lighten the load on the power supply and reduce the heat. The unreliable combined 'grid' and 'cathode' biasing system is now pure cathode bias and the output stage operation changed from Class AB Pentode to pure Class A in Triode mode. The over complicated 3 valve per ch 'front end' is now a 2 valve DC coupled cascode arrangement with minimal feedback. The original amplifier was rated at 100 Watts per channel, this now down to 60 watts, more than ample for home use.

Customer comment;

Hi Geoff
I have installed and started running in the DEFY and I think it is amazing what you have done. I thought it was good before but it is now in another league. Transparency AND slam in one package. I am relistening to every thing in my collection which will take me several years at this rate.
I have rationalised the cost of the work by accepting that originally I had a 'bargain price' Jadis but now i have a world-class power amp that has cost me only 3200! Cheap at the price and I'm very happy. 'Quality is appreciated long after the price has been forgotten' I have emailed Jadis in France about a replacement transformer. Their website claims that their output transformers are guaranteed for life. So we may be lucky and get it repaired/replaced for free. (Not holding my breath on this one!) Thank you for sweating blood over this one. I hope life is a little easier now that Jadis has gone home!

Finally, a quote from a Guy called 'Bear' on the diyaudio website. I would imagine you two would have a lot in common.

"I don't know what is in your amp, I do know what is in the Defy 7. Not a very good circuit. Very good output iron. The way that the tubes are driven causes them to self bias into flame-out under often found operating conditions. If I was given a Defy 7 and was not going to resell it, I'd gut the stage that drives the output tubes and turn it into either a properly operating AB1 driver, or better still a properly operating AB2 driver. The Defy 7 would also greatly benefit from a soft-start B+ circuit. Eats tubes for lunch the way it is stock. My 2 cents worth... _-_-bear"

Thank God you have rescued me from that likelihood. I must admit to having been VERY nervous every time I flicked that switch.

All the best for now

Rogers HG88
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