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Old 27th February 2013, 12:45 AM   #1
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Default Jadis DA88S schematic

Hi all,
Bought two Jadis DA88S OPT from a broken unit. I was hoping to build my own DA88S and need a power tranny and Schematic diagram. Jadis has denied to sell power tranny and schematic. Somebody out there may have a schematic to make monoblocks using this two OPT. If it is possible to build two 2A3 pushpull monoblocks I will be over the moon. But so far I couldn't find anything interesting. Some help would be highly appretiated.
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Old 27th February 2013, 10:40 AM   #2
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If you have or know serial numbers could you ask directly to Jadis, I did and received schematics for my Jadis JA80 mono blocks.
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Old 27th February 2013, 11:07 AM   #3
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I have already asked and Jadis has denied to share documents. Talked with 4 dealers and they said no. I bought the OPT from a seller in france who was the 2nd owner and can't get the serial number from original number. So in short I am stuck.
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Originally Posted by merlin el mago View Post
If you have or know serial numbers could you ask directly to Jadis, I did and received schematics for my Jadis JA80 mono blocks.
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Old 27th February 2013, 11:10 AM   #4
SY is offline SY  United States
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Think of it as an opportunity. Jadis amplifiers are notoriously poorly designed (performance and reliability), so you can use the shiny iron as the basis for an amplifier with good performance. There's nothing magic about their transformers which prevents their use in a competent circuit.
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Old 27th February 2013, 11:16 AM   #5
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Now several possibilities started to haunt me. Somebody find me a gun.


1. Find Jadis DA88 schematic and build my own DA88. I need to source a power transformer from Jadis if they are happy to sell power transformer only as a spare parts.

2. Find a good 2A3 push pull DIY monoblock schematic and use DA88 output transformer

3. Find JA80 monoblock schematic and use DA88 output transformer.

Looks like I brought myself into more pain and hassle by buying those two Jadis output transformer.


But it would be fun if I can build anything with 2A3 tubes.
But google doesn't have enough positive source for 2A3 pushpull which will help a newbie like me.
Quote:
Originally Posted by SY View Post
Think of it as an opportunity. Jadis amplifiers are notoriously poorly designed (performance and reliability), so you can use the shiny iron as the basis for an amplifier with good performance. There's nothing magic about their transformers which prevents their use in a competent circuit.
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Old 27th February 2013, 11:44 AM   #6
SY is offline SY  United States
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Look around for one of DHT Rob's designs- I've heard them driving rebuilt Quad 57s and the combination was terrific.
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Old 27th February 2013, 04:16 PM   #7
roline is offline roline  United States
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Looks like it was a PPP KT88 amp, so you fill need low plate resistance to drive it. I would be guessing at around 2KRaa on the primaries......
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Old 28th February 2013, 02:00 AM   #8
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I have worked on Jadis JA80 monoblocks and have a pdf scan of the manual which is in in English and French and includes the schematic. It is about 600KB so could not post it.

They are 80 Watts RMS Class A Push Pull.
The schematic shows:
4 off KT 88 in parallel push pull,
Ultralinear connection
Cathode Feedback winding for each side of the push pull
Auto bias for each side of the push pull (3 x 1K in parallel and then a 2K7 trim across that for approx 300 Ohms).
Wimpy 12AX7 driver.
510K grid leak for each side of the push pull (2 tubes) which is why these things blow up at the "drop of a hat".
Negative feedback from KT88 anodes to driver tube (12AX7) cathodes
12AU7 front end.

I modified it to have individual auto bias (600 Ohms) for each tube which improved reliability marginally.

What the schematic doesn't show you:
B+ at KT88 Anodes is 520V
My oscilloscope test results ( at 1kHz):
Adjusted Output into 3R5 Dummy Load (Resistive) on 4 Ohm tap to 20V pk-pk (that calcs as 14 W RMS out)
KT88 Anodes 190 V pk-pk
KT88 Screens 100 V pk-pk same phase as anodes (negative ultralinear feedback)
KT88 Cathodes 10V pk-pk same phase as anodes and screens

That means POSITIVE cathode feedback
The EFFECTIVE Ultarlinear feedback voltage (screen to cathode) is therefore 90 V pk-pk or about 50%.

Assuming the DA88 is the same output tranny you could calculate Raa, Ultralinear % and Cathode Feedback % from those measurements.

It is kept stable by that NFB from the KT88 anodes back to the driver cathodes and the Ultralinear NFB.
The positive cathode feedback is I think to increase the input impedance seen at the KT88 grids so that they can get away with that incredibly wimpy driver.

ABSOLUTELY (yes, I'm shouting) do not copy the JA80 schematic, it is seriously unreliable, Grid leaks on the output tubes are X10 too high and the things just melt down time and again, usually taking out $400 worth of tubes each time (US or Aussie dollars worth about the same). Output tube sets have to be selected for matched operation as well as low grid current.

Frankly I was not all that impressed with the sound of these things either - after I'd done a couple of days post repair listening to them on my own system it was a relief to p
pull them out and put back my 10 Watt per channel Baby Huey's.

You could do much better using those trannies for a Citation Clone or try a Menno VdV SuperTriode arrangement or damn near anything but a Jadis.

I'm about to go away for 2 weeks so uncertain as to my internet access for that time but leave me a PM if you want a copy of the JA80 manual and then be patient.

Cheers,
Ian

Did you get the impression I did not like the JA80 and was totally un-impressed with the design?
Oh, good I'm communicating effectively.

Last edited by gingertube; 28th February 2013 at 02:12 AM.
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Old 28th February 2013, 02:16 AM   #9
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Here is the Jadis Defy-7 schematic.
The front end of the JA80 is the very similar but with feedback from output tube anodes to driver tube cathodes. Output is also similat but with only 4 tubes and with them auto (cathode) biased instead.
Cheers,
Ian
Attached Files
File Type: pdf Jadis_Defy7.pdf (29.4 KB, 173 views)

Last edited by gingertube; 28th February 2013 at 02:19 AM.
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Old 28th February 2013, 05:14 AM   #10
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Hi Ian,
Thanks for sharing your thoughts and ideas. I have PM'ed you my email address. I am in Perth, Western Australia. I have Jadis Orchrestra Reference and very happy with the unit. Thought monoblocks may sound different and more romantic. I am also considering monoblocks with 2A3 pushpull. I am not sure if I can use those trannies for 2A3 pushpull but worth considering.
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