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audiojoy 8th March 2008 02:38 PM

Jadis DA7/defy power amplifier mods
 
I have a Jadis DA7 power amplifier and yearn for a little more transparency and sound staging but without sacrificing the great tonal qualities of the Jadis 'in house sound'. I guess I am after a poor man's JA200!

I started with the internal speaker cabling which i changed to audionote spx, this had some nice improvements in detail and a slightly more transparent sound stage. But not night and day. I next played around with the coupling caps six on each side.

Changing the coupling caps if not done carefully can make you lose the wonderful tonal qualities of the Jadis amp, so I changed one cap at a time and analysed it after each change.

I found out, that out of the six caps per side only one cap on each mono side needed changing to affect the entire sound. I tried a single Mundorf silver oil cap one on each side and found this too bright. Tried audionote aluminium foil, even less transparent than the Jadis caps. I then moved up to the audionote copper oil and this brought about a huge change. Sound staging deepened, details sprung up and there was far more presence. I then added a second one on each side and suddenly i was listening to a sound almost the same as my other amplifier. Guess what they sounded almost like my Audio Note silver signature 300b P4 mono blocks with those expensive nickel core output transformers. What does that tell you about the Jadis output transformers!!!!!!!!!!!!!!!

However, the tonal richness that made the whole picture seem so real had gone. I went back to just one audionote cap each side and the tonal colours returned. I then opted for Military PTEP caps (my all time fav caps)starting off with one each side in addition to the audionote copper caps. Yes more clarity more detail but no loss of that jadis signature sound. I was able to replace 4 caps on each side before the sound started to harden up. With 5 ptep and one audionote the sound was too lean and hard but on replacing one of the ptep caps back for the original jadis cap, the magic immediately returned and that's how i have left it so far.

I now have , compared to the original, much improved soundstaging, depth and focus. A far more detailed and dynamic sound, with also much improved timing and rhythm. Seemed a bit leaden in timing prior to modification, which other owners on audioreview have also mentioned. However, I have managed to keep much of the jadis tonal and timbral accuracies. Changing valves helped especially the input driver but nothing to what i achieved above.


Next i will work on the electrolytic caps. There are still the resistors in the signal path to deal with, the fuses and their associated caps etc etc. Also huge bits of metal to secure cables to, surely cannot be any good.

If anyone else has been along this route please let me know.

bear 8th March 2008 09:11 PM

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

Salas 8th March 2008 09:29 PM

Re: Jadis DA7/defy power amplifier mods
 
Quote:

Originally posted by audiojoy
If anyone else has been along this route please let me know.
I have done some upgrade work in JA 200, DA-30, JS-1MKIII. You can email me.

audiojoy 8th March 2008 09:33 PM

Thanks Bear,

I have already achieved the equivalent in terms of sound quality IMHO to my 6K audionote silver signature. So I am not at the present time in a hurry to do major surgery. Although i believe alot of the Jadis sound is down to the output transformer, i was able to demonstrate that i could make the jadis output a sound very similar in all characteristics to the signature audionote sound. From this i can only assume that components and circuitry must play a part in its 'house' sound, which once again i must confirm I highly regard. So tinkering with the circuit as it is for now will do for me, but who knows later???

I think in this thread i am interested in maintaining the signature Jadis sound and aim to get closer to the JA200 sound, so any help along those lines would be of great benefit tome. I know power output etc must play a role here in the difference but none the less i would like to give it a go.

audiojoy 8th March 2008 10:33 PM

Hi Salas,

diyaudio will not actually allow me to email you via this site, because i am new to this site. I am very interested in hearing your views.

analog_sa 9th March 2008 08:17 AM

What on earth are "Military PTEP caps "?

audiojoy 9th March 2008 11:45 AM

The ptep caps are made in Russia for the military. Material utilised in their construction is ptep. See Ebay, mostly sold from Eastern Europe. Very cheap, voltages can go up to 1000v, loads of values. IMHO, better than aluminium audionote, equal to and better in other areas to the mega expensive copper audionote caps. They are extremely transparent and detail, but can in certain circuits lead to a slight diluting of tonal colours.

analog_sa 9th March 2008 12:20 PM

Quote:

Originally posted by audiojoy
The ptep caps are made in Russia for the military. Material utilised in their construction is ptep. See Ebay, mostly sold from Eastern Europe.

Extremely vague. What is ptep? Polyterephthalate? What is written on the caps?

Is it in fact PTFE?

audiojoy 9th March 2008 02:24 PM

deepest apologies you are correct ptfe.

Salas 9th March 2008 05:01 PM

Quote:

Originally posted by audiojoy
Hi Salas,

diyaudio will not actually allow me to email you via this site, because i am new to this site. I am very interested in hearing your views.


Its not easy to put this stuff in some comprehensive and sort text. I will try though. You know the Jadis house sound. Its meaty, big, expansive, rather slow. Never irritating or electronic though. Tuned for symphonic. The cornerstones are the PSUs and the OPTs. But the anchor color signature stems from the internal construction method. There is a cook up of lesser grade than boutique, reliable industrial grade, coupling and reservoir caps, plus thick cabling for PSU, and relatively thin coax for signal. The Achilles heel that lends the less than pristine float and detail is the tiny driving circuit for multiple output tubes. They are not so heavy into class A as it is believed. Around 50% of rated dissipation. Also the auto bias cathode resistor cap bypassed output is a point that lends it self to serious manipulation.
To keep the base house sound which has classic merit indeed, that just needs to fly, my experience is:
Don't change Ohm or micro Farad for small signal circuit. Don't change the PSU caps or the PSU cabling. Use Black gate FK output cathode bypass caps at double the original value of the stock Philips / BC ones. Use Russian Floroplast signal coupling coupling caps with 0.01uF Russian Silver Mica bypass on each one. Use an assortment of NOS German driving tubes if you keep the original finals. Even better, substitute the finals for best KT88 you can afford from New Sensor stock but with NOS English driving assortment. Use solid core 0.8mm silver from OPT to binding posts. Don't change input signal cabling if any. Substitute the in series with the signal resistors with Riken. Keep all components that you have taken out in good shape, you may need to put back a couple if the rest of your system is not that balanced and you need to keep the upgrade signature a little tamed.

Regards.


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