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The Jadis JA200Mk2 review---or slam!

In the current issue of Stereophile, Jason Victor Serinus reviews the new Jadis JA200Mk2....or should I say SLAMS the amp!!

Since I am new to the Jadis family, I thought I would bring up a few interesting thoughts on this review. The first is that I am totally understanding why an amp that uses Ten(10) KT150’s per side would probably not be a great solution at all!!!! Why, well JVS brought up the reason...although he did minimize the impact; the amount of heat this beast gives off is crazy! Space heater in disguise. What’s odd is how JVS also points to his Pass amps as giving off a ton of heat. ?? Anyhow, we then learn that the review was conducted using JVS DAC as the source...and direct into the amps....who does this??? Why on earth would anyone use a DAC to drive a large tube mono block for a magazine review!! No preamp was used. All of the photos of the amp show it using the KT120 tubes...all. There is mention of what the amp was designed with...the KT150’s, but there is some questions to what tubes were actually in the amp under review. Then to go on, the amp was apparently strapped for the 1ohm load....????? JVS doesn’t check these things!...and then states that the amp is not really that great in the bass reproduction. Huh, why would he think that a tube amp that is strapped to the 1ohm setting would produce prodigious bass with his hard to drive Wilson Alexia’s!!! Can we say classical "mismatch" here.
JA’s follow up measurements, while interesting as usual, are IMO also a little odd, what is the base line that he is using to determine accuracy??? Another tube amp...a ss amp, a hybrid design of some sort...his ears, someone else’s ears???

While I purposely did not consider the new Jadis JA 200Mk2 amp for my system, due to the immense heat output...and probable impact on reliability due to this factor ( IME, electronics seem to have a much longer life if heat is not that much of a factor!!! ( Am i one of the few that perhaps understands this??) Plus, i don’t need any space heaters in S.Calif.) I would think that a follow-up review ( preferably by a more experienced reviewer) would be in order....one who can correctly match-up this amp to their ancillary gear.
Anyone else have an opinion of the Jadis JA200Mk2 review in the current issue of Stereophile?
128x128daveyf
trelja
3,223 posts
 
@daveyf, I think you are showing us that you have not actually heard any of the latest Jadis amps. The new KT150 based versions are far more neutral sounding than any of the amps that came before from Jadis. So, while the latest models may not be as warm as in the past, they are certainly different sounding than even from a few years back."

You’re right. While I’ve been around some of the KT120 offerings, I’ve not yet heard the amplifiers running KT150 output tubes. I’m not much of an ARC fan, but know a guy who moved from 6550 to KT120 to KT150 in his amplifier. Although I certainly still have no interest in that product, the KT150 readily eclipse the other two in it. But I also haven’t ever felt interested in buying a set for myself, either.

@howthefidelity, "I’m sure if I installed EL34s I’d get more midrange with the amp."

Yes, but at the expense of the low-end. Still, those JJ E34L are the tubes I run in mine. Unlike the more expensive amplifiers, JOR uses the Dynaco circuit, with fixed bias, and a completely (more neutral) different sound than its cathode bias big brothers. That said, that circuit with the right EL34 tubes produces some of the most glorious midrange attainable that even the more expensive products cannot touch.

What 12AX7 have you tried so far?
daveyf's avatar
daveyf OP
2,871 posts
 
trelja, as you may know, you cannot roll in the KT120's and particularly the KT150's into the older designs, without potentially doing damage to the transformers. Only the new Mk2 models have been modified by Jadis to accept the KT150's. 

howsthefidelity
6 posts
 
@trelja, regarding 12ax7s I tried some old Mullards that I have. They sounded great but overall changed the balance in a way, where I preferred the synergy with the Tung-Sols. It’s been a while, so I can’t recall pros/cons in this case.

Your fixed vs cathode bias design explanation makes a lot of sense. I feel and hear in my current system synergy the JOR works great as is (KT90) and I tune my sound via the phono stage, cables, cartridge and so on. Also the fact that it takes a visit to an amp-tech to bias the damn thing makes me want to keep it pretty stock. But again, this is hi-fi and can change pretty quick and before you know it I may have JJ E34L running in the JOR :-).

Do you know how much power the JOR uses at idle?

Regarding the original topic of this thread it just shows how important it is to always test gear in your own surroundings.


trelja
3,223 posts
 
@howsthefidelity, you’re right about the Mullards. Please give the Shuguang (or Psvane) triple mica 12AX7B aka Silver Dragon a go. At $10, you will absolutely not believe their performance. They easily best the Mullards, and compete with the best ever variants. Impossible sounding, I realize...

A journey of building and modding amplifiers completely rewrote my thoughts and beliefs, and I now feel fixed versus cathode bias sits among the top of the factors of how a tube amplifier performs and sounds. Fixed bias sounds a lot tighter, faster, reactive, and neutral. Cathode bias sounds more relaxed, warm, liquid, lush, romantic, and slower. Neither presents a better or worse presentation, it’s why they make vanilla AND chocolate.

If you can handle working around high voltage, you can easily bias the JOR yourself. The effort lies in taking it apart, and (especially) putting it back together. Removing the side panels and bottom plate, simply rest the amp on its side on something like a piece of carpet, with the power transformer sitting on the lower side for obvious reasons. Measure the voltage across the ~5.6R resistor that sits between the output tube’s plate (via the yellow wire) and the output transformer. Adjust the potentiometer to 90 - 120 (Jadis considers 110 best) mV, and you’ve biased the tube. Repeat for the other 3 output tubes, and you’ve biased the amp. There’s an additional step some employ, but as it confuses the heck out of people, and rarely yields anything, let’s disregard it. Beyond this, the figures I just listed leaves the amp biased extraordinarily (and surprisingly at 40% plate dissipation for an EL34’s rated 25 watts, and far colder for your KT90) cold, which Jadis acknowledges. Personally, I bias the amp a lot hotter, though still conservatively, but I won’t say anything further than that for now. Also, I’ve suggested folks consider cutting holes in the bottom plate that line up with the bias resistors and potentiometers, as the ability to bias the JOR without taking it apart would reduce it to something that takes just a couple of minutes.

Officially, the JOR uses 300W at idle.
howsthefidelity
6 posts
 
@trelja thanks a lot for the pre-amp tube recommendation (I'll check those tubes out) as well as how to bias the JOR. I could bias a new set of tubes myself but it's more taking the amp apart that worries me and why I better leave that for the tech. Also I expect the KT90s to last for at least 3-4 years and a general check-up can be done also when installing and biasing the new set of tubes. My sound preferences is definitely towards the fixed bias designs.  

Jadis refers to 300W at maximum. I don't believe (or hope that is) it draws so much power at idle. But maybe I should just contact Jadis. 
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