Jadis PA 100 amp - Jadis becomes Jadis again

[jadis]

Bewitchingly musical sound....

And I feel this PA100 gives out more power that my old JA 200 which was Class A.

 

[jadis]

A manual bias amplifier does not have to have trimpots. Sometimes manufacturer/designer calculates the impedance required for the circuit based on tube’s general characteristics and installs a resistor for each tube instead of an adjustable pot. I believe jadis PA 100 is designed like that. this kind of design is more like a manual bias cause it’s manually set in the factory and you need to change the resistor in order to change the bias. That’s a better approach in terms of purist circuit design but it has a major down side. You need to use perfectly matched pairs or quads that will behave same while they age which is almost impossible to accomplish. Most probably that’s why it has a fuse for each tube. If one of them ages differently and goes bad due to factory set constant bias, it triggers it’s fuse and saves the circuit. IMHO regarding it’s circuit design it can be called constant bias amplifier.
On the other hand a normal manual bias amplifier has pots to adjust bias according to changing conditions such as line voltage, tube age and characteristics.
Auto bias measures cathode current/plate voltage etc and regulates it automatically using a dedicated circuit which I couldn’t see in PA 100.

After weeks of info searching, which was helped by the fact that I decided to buy 12 new KT88s and had to ask a relative who lives in France to call the factory and ask many questions about the procedure or non procedure, I have come up with the conclusive answer. This amp is really a manual biasing amp, and it has trimming pots. The shock of my life when I was told about it by a dealer as I was asking him if resistors needed to be replaced or soldered. He said no. There are trimming pots underneath. I had to look at my pictures again and enlarge it to find them. And lo and behold!





The pots are in another small circuit board near the transformer and I had been looking the the 12 power tubes' socket all along.

And so, it is indeed much like the Defy 7's biasing procedure, as this amp is like the 3rd generation of it.

So what is utterly a cause of confusion is that their own site mentions that this PA100 is Manual Biasing,



And their model JA 500 is also Manual Biasing, BUT there is a further explanation.



"Adjustment when the tube type is changed." While this can refer to changing KT88 into EL34 or others, the PA 100 can also be fitted with EL 34 from the standard KT88 but nothing was indicated in its spec sheet. What should clearly have been stated in the PA100 spec sheet is that biasing is MANUAL, adjustment need when tubes or tube types are changed. Because now it is clear to me, this amp is NOT Auto Bias. And I found out that in the Jadis line, only the CLASS A amps and integrated amps are auto biasing. PA100 and the JA 500 are Class AB amps. The local dealer here has told me he has a tech man who can do the biasing service. Indeed, opening the bottom plate and turning it to its side with power switched on is a very challenging if not dangerous thing to do for a layman.



The green board has the trimming pots.

 

[AudioLibertarian]

After weeks of info searching, which was helped by the fact that I decided to buy 12 new KT88s and had to ask a relative who lives in France to call the factory and ask many questions about the procedure or non procedure, I have come up with the conclusive answer. This amp is really a manual biasing amp, and it has trimming pots. The shock of my life when I was told about it by a dealer as I was asking him if resistors needed to be replaced or soldered. He said no. There are trimming pots underneath. I had to look at my pictures again and enlarge it to find them. And lo and behold!



View attachment 89438

The pots are in another small circuit board near the transformer and I had been looking the the 12 power tubes' socket all along.

And so, it is indeed much like the Defy 7's biasing procedure, as this amp is like the 3rd generation of it.

So what is utterly a cause of confusion is that their own site mentions that this PA100 is Manual Biasing,

View attachment 89439

And their model JA 500 is also Manual Biasing, BUT there is a further explanation.

View attachment 89440

"Adjustment when the tube type is changed." While this can refer to changing KT88 into EL34 or others, the PA 100 can also be fitted with EL 34 from the standard KT88 but nothing was indicated in its spec sheet. What should clearly have been stated in the PA100 spec sheet is that biasing is MANUAL, adjustment need when tubes or tube types are changed. Because now it is clear to me, this amp is NOT Auto Bias. And I found out that in the Jadis line, only the CLASS A amps and integrated amps are auto biasing. PA100 and the JA 500 are Class AB amps. The local dealer here has told me he has a tech man who can do the biasing service. Indeed, opening the bottom plate and turning it to its side with power switched on is a very challenging if not dangerous thing to do for a layman.

View attachment 89441

The green board has the trimming pots.

But I only counted 5 trimming points if those are indeed these... The blue ones....

 

[jadis]

But I only counted 5 trimming points if those are indeed these... The blue ones....

More mystery. I suddenly recall now that had noticed those 3 years ago when I checked the demo unit in a dealer. But I said to myself those can't be trimming pots because there must be 12, or 6 pots near the tubes. So I dug up some info on the biasing method of the Defy 7. It was mentioned that each pot controlled the bias of 3 tubes. I don't know why since Jadis insisted on matched pairs. The 5th pot, I have no idea what that's for.

It is highly irresponsible for Jadis to FAIL to mention biasing in its owner's manual. It's not only a disservice to the buyer and user, but outright dangerous to replace that whole get of 12 tubes without biasing, from the bottom with high voltage, as the new tubes with too high a bias setting with red plate in no time. I have been confused and mislead from day 1, sad to say. But this amp is the best amp I've ever used.

 

[jadis]

So, depending on the outcome of how easy or how hard it is to get a technician to my house to do the rebiasing of the 12 tubes, the title of this thread may become 'Jadis is Not Jadis, Again!'

 

[jadis]

Btw, I learned from the local dealer, who emailed my questions to Jadis, that to bias this amp, the test points are the 12 fuse holder's bottom live points, while the other test stick goes to the chassis, or a screw of the chassis. And then adjust the readings via the 4 or 5 trimpots. And oh, of course the last thing, how much is the bias? I'd rather not mention it here, but the dealer told me a certain figure, lower than that which ARC uses. All these, are NOT in the owner's manual, believe it or not. For a $15,000 amplifier. IT is safe to assume that these past 2 months. I have not been listening to the music, but have been watching my amp.

 

[AudioLibertarian]

Btw, I learned from the local dealer, who emailed my questions to Jadis, that to bias this amp, the test points are the 12 fuse holder's bottom live points, while the other test stick goes to the chassis, or a screw of the chassis. And then adjust the readings via the 4 or 5 trimpots. And oh, of course the last thing, how much is the bias? I'd rather not mention it here, but the dealer told me a certain figure, lower than that which ARC uses. All these, are NOT in the owner's manual, believe it or not. For a $15,000 amplifier. IT is safe to assume that these past 2 months. I have not been listening to the music, but have been watching my amp.

The moral of the story: Unless one is a certified techie who is a weight lifter and with (sometimes) a suicidal tendencies (during the highly dangerous baising procedure), DO NOT BUY JADIS MANUAL BIASING AMPS!!!! . Jokes aside (although the above is certainly kinda holds true) I hope someone at Jadis is reading this forum and draws certain conclusion, yeh I know , good luck with that ...... I am kinda happy I did not buy that PA 100 dealer demo unit, as tempting as its price was!

 

[jadis]

The moral of the story: Unless one is a certified techie who is a weight lifter and with (sometimes) a suicidal tendencies (during the highly dangerous baising procedure), DO NOT BUY JADIS MANUAL BIASING AMPS!!!! . Jokes aside (although the above is certainly kinda holds true) I hope someone at Jadis is reading this forum and draws certain conclusion, yeh I know , good luck with that ...... I am kinda happy I did not buy that PA 100 dealer demo unit, as tempting as its price was!

Lol.

So you never had your Defy 7 biased again after the purchase?

 

[AudioLibertarian]

Lol.

So you never had your Defy 7 biased again after the purchase?

I did try to adjust the biasing once by myself, almost got electrocuted, and had a tech do it.... Then sold it, as it was a tube eater and tubes reliability was very poor in those days, early mid 90s ... But it did sound almost better than anythng else, save for the Tube Research Labs amps (which was another adventure in masochism of sorts, hahahaha) and Jadis monoblocks.

 

[jadis]

I even emailed Brooks Berdan as they have that YouTube video of the PA100. They told me they're dropped the line as they have relocated and directed me to another dealer, who did not bother to answer my questions on the PA100.

 

[sel53]

After weeks of info searching, which was helped by the fact that I decided to buy 12 new KT88s and

I have been watching this very interesting thread, and have a question …

Why did you decide to replace all 12 power tubes? It seems like you might have already successfully replaced a pair or two, so this is a big step. How has your reliability been?

Regards

 

[jadis]

I have been watching this very interesting thread, and have a question …

Why did you decide to replace all 12 power tubes? It seems like you might have already successfully replaced a pair or two, so this is a big step. How has your reliability been?

Regards

I was thinking to change them as they are at past the 2,000 hour level. Replacing a pair with new EH KT88s was ok, but a few days later I notice 1 other tube having signs of red plating starting at the bottom and a few days later, another one. So I changed them too. Now, I do not know how the bias is on those replaced tubes, and they're all on the left channel. I really hate to part with this amp as I feel it's the best amp all around and my budget will make me get something I feel will not be up to this amp's performance. I have asked for a quote on 12 new EL 34 from the Jadis factory since the local dealer will do the re biasing. Might as well give it one more shot , till the next re biasing in 3 years time.

 

[sel53]

I was thinking to change them as they are at past the 2,000 hour level. Replacing a pair with new EH KT88s was ok, but a few days later I notice 1 other tube having signs of red plating starting at the bottom and a few days later, another one.

That is very interesting, sorry you are having problems.

A ways up in the thread, you showed your matching specs for the tubes you got with the amp. Those numbers struck me as being matched in sets of three, versus pairs. I obviously don’t have a schematic, but it would not be uncommon to have three tubes in parallel for each 1/2 of a push-pull, per channel. So you might want a matched set of three so the draw current uniformly. Does this make sense to you?

I wonder if someone like Upscale Audio could help you with matching. I have bought some (not power) tubes from them with excellent apparent matching.

Good luck!

 

[jadis]

That is very interesting, sorry you are having problems.

A ways up in the thread, you showed your matching specs for the tubes you got with the amp. Those numbers struck me as being matched in sets of three, versus pairs. I obviously don’t have a schematic, but it would not be uncommon to have three tubes in parallel for each 1/2 of a push-pull, per channel. So you might want a matched set of three so the draw current uniformly. Does this make sense to you?

I wonder if someone like Upscale Audio could help you with matching. I have bought some (not power) tubes from them with excellent apparent matching.

Good luck!

Thanks. I recall reading the Defy 7 was biased in sets of 3 too, and this is its 'grandchild'. Your point makes sense now to me.. So A1, A2 and A3 are the matched trio. I never noticed that. Since this is a manual biasing amp, with a fixed point of 42.5 mA ( the local dealer told me this, for KT88s), I figured that wherever I bought the set of 12 tubes, they will be matched according to each seller's testing method. They will have different numbers, as one seller already told me. The important thing now that remains is that the technician knows the biasing number, and has the schematic, and is properly advised by Jadis in France on these details. The technician also needs to be the one linked to the local dealer, as only the local dealer will be given such info by Jadis France. I was told that Jadis France will sell those 12 tubes to my contact in France, but he has to sign a waiver that they are not responsible for your tech man or the lack of it. And, they will NOT teach you nor furnish any instructions to you as to HOW to bias the amp. This , after taking 1500 euros of your money. I told my source, no thank you, I will not buy those tubes from them under those conditions. So they must be justifying why they never placed any info on biasing on the PA 100's owner's manual. Nothing is talked about regarding bias unlike ARC and CJ. It is like you have bought a solid state amp from therm. Shocking to me really.

And btw, Jadis said they do not have any matched 12 tubes to the numbers I had. It's a bit far, so , they say all the more you need to bias it with the help of a tech man.

 

[microstrip]

Thanks. I recall reading the Defy 7 was biased in sets of 3 too, and this is its 'grandchild'. Your point makes sense now to me.. So A1, A2 and A3 are the matched trio. I never noticed that. Since this is a manual biasing amp, with a fixed point of 42.5 mA ( the local dealer told me this, for KT88s), I figured that wherever I bought the set of 12 tubes, they will be matched according to each seller's testing method. They will have different numbers, as one seller already told me. The important thing now that remains is that the technician knows the biasing number, and has the schematic, and is properly advised by Jadis in France on these details. The technician also needs to be the one linked to the local dealer, as only the local dealer will be given such info by Jadis France. I was told that Jadis France will sell those 12 tubes to my contact in France, but he has to sign a waiver that they are not responsible for your tech man or the lack of it. And, they will NOT teach you nor furnish any instructions to you as to HOW to bias the amp. This , after taking 1500 euros of your money. I told my source, no thank you, I will not buy those tubes from them under those conditions. So they must be justifying why they never placed any info on biasing on the PA 100's owner's manual. Nothing is talked about regarding bias unlike ARC and CJ. It is like you have bought a solid state amp from therm. Shocking to me really.

As far as I remember - many years now are passed since my Defy 7 is gone - the Defy 7 had a mix of autobias and manual bias. The cathode autobias component was assured by the green power cathode resistors that were bypassed by electrolytic capacitors to avoid local cathode feedback in the audio frequencies, but the bias grids were operated at a negative adjustable voltage. Bias was adjusted at the factory - if the tubes were selected and matched to Jadis specification we would not need to adjust bias.

BTW, if we do not have easily accessible test points, using a cheap house power meter can be a great help to get an idea if bias needs adjustment - or as me, also use an IR quality temperature meter to check tube temperature comparatively.

 

[jadis]

As far as I remember - many years now are passed since my Defy 7 is gone - the Defy 7 had a mix of autobias and manual bias. The cathode autobias component was assured by the green power cathode resistors that were bypassed by electrolytic capacitors to avoid local cathode feedback in the audio frequencies, but the bias grids were operated at a negative adjustable voltage. Bias was adjusted at the factory - if the tubes were selected and matched to Jadis specification we would not need to adjust bias.

BTW, if we do not have easily accessible test points, using a cheap house power meter can be a great help to get an idea if bias needs adjustment - or as me, also use an IR quality temperature meter to check tube temperature comparatively.

Great advise. How does the house power meter work to check bias?

 

[microstrip]

Great advise. How does the house power meter work to check bias?

You have to take note of the power consumption with proper bias. 5mA extra in half the Defy 7 tubes will make an extra 15W. But the readings must be taken with same mains voltage supply.

This is not an exact procedure but will give you an idea of gross maladjustment. Some of these cheap measuring devices (less than 20 euros) are accurate to 1%. Surely they should not be used in normal operation!

 

[sel53]

Thanks. I recall reading the Defy 7 was biased in sets of 3 too, and this is its 'grandchild'. Your point makes sense now to me.. So A1, A2 and A3 are the matched trio. I never noticed that. Since this is a manual biasing amp, with a fixed point of 42.5 mA ( the local dealer told me this, for KT88s), I

A while back I found what is purported to be a Defy 7 schematic (I’m not sure how to put it here). I just looked at it, and it shows three tubes in parallel for each 1/2 push-pull, with a bias voltage going to each half. So that would make sense with the 4 pots in your photo … one per triplet per channel. I don’t know what the 5th pot is for; the schematic doesn’t show the biasing circuit itself.

To me that means you should have matched triplets. On the paper you posted, those looked like Gm (transconductance), and maybe plate current? The Gm any tester should be able to check. The plate current, if that’s what it is, would need a specific circuit condition. But I saw on one of the Upscale videos that he does AR matching differently “because they run them hot”, so maybe he could actually set up a specific test. (Not trying to sell him, just info for you, FWIW).

It does make you wonder, though, why they didn’t just do a trim pot for each tube, so at least the operating condition could always be made “safe”.

 

[jadis]

A while back I found what is purported to be a Defy 7 schematic (I’m not sure how to put it here). I just looked at it, and it shows three tubes in parallel for each 1/2 push-pull, with a bias voltage going to each half. So that would make sense with the 4 pots in your photo … one per triplet per channel. I don’t know what the 5th pot is for; the schematic doesn’t show the biasing circuit itself.

To me that means you should have matched triplets. On the paper you posted, those looked like Gm (transconductance), and maybe plate current? The Gm any tester should be able to check. The plate current, if that’s what it is, would need a specific circuit condition. But I saw on one of the Upscale videos that he does AR matching differently “because they run them hot”, so maybe he could actually set up a specific test. (Not trying to sell him, just info for you, FWIW).

It does make you wonder, though, why they didn’t just do a trim pot for each tube, so at least the operating condition could always be made “safe”.

Thanks. I think you're right on the 4 pots for the 12 tubes. I believe the reason why they didn't make 12 trim pots I guess is to make life easier for the technician. They don't make life easier for the user because they don't want to drill holes on the top plate like ARC did on their models, to make them look real elegant. So when one wants no biasing, he should buy any of their Class A amps.

 

[jadis]

I read in some old forum posts, that a Defy 7 user had trouble reaching the bias number for the 3rd tube. And was asking help. In the light of all these, I think the solution is to find a new matched triplet again. Such pain for this biasing method that Jadis uses. In this day and age, speciall with the pandemic, user would like to call in a technician to do the biasing.