Jadis JA 200 monoblock power amplifier Measurements

Sidebar 3: Measurements

The JA 200's main chassis was quite hot following the 60-minute, 1/3-power preconditioning, but the power-supply chassis barely got warm. The Jadis continued to run hot throughout the other bench tests, suggesting high-bias operation and the possibility of frequent tube replacement (though we have no empirical data to suggest that this will be the case). Its input impedance measured above 600k ohms—high enough to be difficult to measure accurately with our Audio Precision test set. This is unusually high, even for a tube amplifier, and unlikely to cause matching problems with any conceivable preamplifier or other source. The Jadis's voltage gain when loaded with 8 ohms measured 30.3dB. DC offset at the Jadis's outputs measured between 0mV and just over 3mV, varying considerably due to 1/F noise, but generally staying below 1mV.

The JA 200 is non-inverting, a positive-going input resulting in a positive-going output. S/N ratio measured a fine 108dB (unweighted ref. 1W into 8 ohms). The Jadis's output impedance was admirably low for a tube amplifier, varying from 0.18 to 0.25 ohms depending on load and frequency. (The JA 200 can be internally strapped to accommodate various loads; our samples were strapped to produce an 8 ohm output tap, and were auditioned and measured in this configuration. Changing the output strapping to create a higher impedance tap will somewhat increase the output impedance.) The higher the output impedance, the greater the potential for frequency-response–skewing interaction with a loudspeaker load. The Jadis should be less prone to this than are amplifiers with higher output impedances—an affliction found all too often in tube amplifiers.

Fig.1 Jadis JA 200, frequency response at 2.83V into 8 ohms (0.5dB/vertical div.).

Fig.1 shows the frequency response of the Jadis at 1W into 8 ohms (the curve for 2W into 4 ohms, not shown, is virtually identical, with about 0.1dB less rise at 20kHz). The rising response above 20kHz peaks just above the 50kHz limit of the plot and drops sharply above the peak; this is very likely an output transformer anomaly.

Fig.2 Jadis JA 200, small-signal, 1kHz squarewave into 8 ohms.

Fig.3 Jadis JA 200, small-signal, 10kHz squarewave into 8 ohms.

The output of a 1kHz squarewave is shown in fig.2. The damped oscillation visible at the top of the waveform is also visible in the 10kHz squarewave (fig.3), and is associated with the peak in the high-frequency response. (The frequency of the oscillation at the top and bottom of the curve in fig.3 comes out to just above 60kHz.)

Fig.4 Jadis JA 200, THD+N (%) vs frequency at 2.83V into: 8 ohms, 4 ohms, 2 ohms.

Fig.5 Jadis JA 200, 1kHz waveform at 1W into 8 ohms (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.6 Jadis JA 200, 1kHz waveform at 4W into 2 ohms (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

The THD+noise curves in fig.4 show a sharply rising distortion at higher frequencies, but reasonable performance up to about 10kHz. Only the harmonic-distortion products of frequencies below 8kHz or so will be audible, the second harmonic of 8kHz being 16kHz. The THD+noise waveform at 1W into 8 ohms (fig.5) and 2W into 4 ohms (not shown) is primarily second harmonic plus noise; at 4W into 2 ohms (fig.6) it becomes primarily third harmonic.

Fig.7 Jadis JA 200, spectrum of 50Hz sinewave, DC–20kHz, at 106W into 4 ohms (linear frequency scale).

The third harmonic also predominates at high powers and low frequencies. A plot showing the output resulting from a 50Hz input (106W into 4 ohms—two-thirds rated power) is shown in fig.7. While the second harmonic is at –49dB (about 0.3%), the third harmonic is higher in level at –44dB (about 0.6%), with higher harmonics lower in level and roughly decreasing. This is a relatively high level of distortion in comparison with many other amplifiers we've measured, though not exceptionally high on an absolute scale.

Fig.8 Jadis JA 200, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 3.8W peak into 8 ohms (linear frequency scale).

Fig.9 Jadis JA 200, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 7W peak into 4 ohms (linear frequency scale).

A similar spectral plot in fig.8 shows the IM at the output resulting from a 19+20kHz input. The Jadis would only put out very low power with this input signal before clipping; 3.8W into 8 ohms is shown here. (At 5.8W, not shown, the distortion artifacts were greater; though serious clipping had not yet been reached by this point, it was being approached rapidly.) The 18kHz and 21kHz artifacts are at about –37dB, or about 1.5%, the 1kHz slightly lower at –38.7dB, or about 1.2%. With an output of 7W into 4 ohms (fig.9), the largest artifacts are again at 21kHz, 18kHz, and 1kHz (–29.5dB, –29.7dB, and –30.7dB, respectively, or about 3%). Because of the nature of this signal, most amplifiers will not put out their rated power with it, but most do put out a significant percentage of that power. The Jadis does not; its performance on this test would have to be rated as poor. The audible significance of this performance is less clear; few tweeters will handle more than a few watts of power at these frequencies.

Fig.10 Jadis JA 200, distortion (%) vs 1kHz continuous output power into 8, 4, and 2 ohms.

The JA 200's THD+noise vs output power sweeps at 1kHz are shown in fig.10. The gradual rise in distortion without a well-defined breakpoint, or "knee," is often seen in tube amplifiers. Here the distortion rises gradually above about 1W. The output is nearly the same into either 4 or 8 ohms, less into 2 ohms. But note that the output does not reach its rated 160W at a reasonable level of distortion. Using our normal 1% THD+noise figure as a standard level for clipping, the discrete measurements for the JA 200 were 109W (20.4dBW, 117V line) into 8 ohms, 110.3W (17.4dBW, 116.5V line) into 4 ohms, and 84.9W (13.3dBW, 117V line) into 2 ohms.

To confirm that this was not an atypical amplifier or power supply, I also measured the 1% THD+noise output level for the other amplifier of the pair (SN 110576, the primary amp measured being SN 110577). The corresponding values were only marginally higher: 114.5W into 8 ohms, 114.7W into 4 ohms, and 85.8W into 2 ohms (all with a 116V line). Because of these lower-than-expected readings, I also measured the output at 3% THD+noise. Here the Jadis reached 132.1W into 8 ohms (21.2dBW, 119V line), 135.7W into 4 ohms (18.3dBW, 118V line), and 100.5W into 2 ohms (14dBW, 118V line). While the JA 200 did reach its rated power output of 160W, it did so at a THD+noise level of 11%.

The Jadis's rated 160W output, based on our bench tests, is a little optimistic; I'd call it 135W at best. The difference would not be immediately noticed in listening tests which don't push the amplifier hard into difficult, low-sensitivity loads. Nevertheless, its test-bench performance was rather disappointing overall for an amplifier this expensive. That it performs as well as it does in listening tests indicates either that the threshold of audibility for certain measurable anomalies is high, or that these anomalies themselves help "create" a pleasant sound. I prefer to believe the former; the latter is not high fidelity.—Thomas J. Norton

US distributor: Bluebird Music Ltd.
275 Woodward Avenue
Buffalo, NY 14217
(416) 638-8207

mrkaic's picture

"I've never been a fan of the 6550A, which is really not an audio tube at all."

How is the audio vs. no audio tube supposed to matter? Correct me if I'm wrong, but what matters for amplifier design are the characteristics of the tube, e.g. plate current vs plate voltage etc.

Incidentally, I remember reading a rather disappointing review of a Jadis amplifier on this website. (https://www.stereophile.com/content/jadis-se300b-monoblock-amplifier-measurements) Why no measurements here?

supamark's picture

This review is like 25 years old, and if you really want an answer to your question about why Mr. Olsher doesn't like certain tubes you can find him at The Absolute Sound, a rival magazine that prides itself on reviews based only on listening - they don't need, or want, your stinkin' measurements. They'll loooove you over there...

NB - I like measurements.

mrkaic's picture

Thank you for the information. I will try to contact Mr. Olsher. I'm hope he will be glad to explain his views.

John Atkinson's picture
mrkaic wrote:
Why no measurements here?

Our image archive only goes back as far as October 1995, when we started producing Stereophile using DTP. (DeskTop Publishing). The Audio Precision test files for the JA 200 weren't in my archive for some reason, so I had to look for the original workbook. Unfortunately, when I found it, it turned out TJN had saved the files on a 5¼" floppy disk and I no longer have a drive for that format.

I didn't want to hold up posting the review to the website, so we did so before I could scan the original printouts of the graphs and formatted the image files. I have now added the measurement sidebar with all of its graphs.

John Atkinson
Editor, Stereophile

mrkaic's picture

You make a super valid point -- some important information might get lost because we no longer have drives to read old magnetic media. I ditched my old floppy drives a few years ago and maybe it was not such a good idea.



tonykaz's picture

I've only ever had one Tube Amp that I could love, it had EL34s.

I've sold the entire 1985 line of Conrad-Johnson Amps that had 6550 output tubes, these Amps were OK but not beautiful like the little EL34 based MV-45a.

Mr.JVS in Port Townsend is about to report on these Jadis Amps. , I'll bet that he can't love em enough to own em.

Tubes run great until one day when they don't, a good SS Amp runs great for decades.

Tony in Michigan

ps. 6SN7 pre-amp tubes are the way to go

Charles Hansen's picture

While the Jadis preamplifiers had very "standard" circuit topologies, their power amps (at least of that era) were different than anything else I had ever seen before. Specifically, they used *positive* feedback to increase the overall gain of the circuit.

(This same techniques was used in many old radio receivers of the '20 and '30s, where it was called a "super-regenerative" design that was almost completely supplanted by the later and superior "heterodyne" design - which was called "super-heterodyne" for purely marketing reasons! One did not want to go backwards from a "super" circuit to an "ordinary" circuit, regardless of which was actually better - ain't marketers slick, even back before WW2? We have Edward Bernays to thank for much of insanity of today's modern society.)

In the Jadis audio power amplifiers, the positive feedback increased the gain for a different reason - so that they could use more *negative* feedback without adding another gain stage or reducing the overall gain. A bizarrely interesting and uniquely French way of doing things differently. These twin feedback colorations were responsible not only for the Jadis's unique sound, but also helps explains its extraordinary sensitivity to AC power line conditions (including line conditioners and power cords).

Bit of obscure audio history for you there, and a large tip of the hat to Ken Stevens of CAT for explaining it so clearly to me. Enjoy!

EDIT: Apologies for the "history lesson" error. There never was a "super regenerative" radio receiver - only a "regenerative" one. The term "super heterodyne" was coined by its inventor, Edwin Armstrong (later to invent frequency modulation, or FM). The "super" part was short for "supersonic" (he actually meant ultrasonic, as supersonic means faster than the speed of sound). "Hetero" means mixed, and "dyne" is from the Greek word for "power" (dynamo, dynamic, dynasty - even "dynamite").

tonykaz's picture

Thanks for the explanation.

Now, can you help explain the Jadis Price Structure? if there is one.

Any typical Retail item will have a 20% of Retail Sale price as Cost to Manufacture ( Proctor & Gamble are at about 9% ).

Importing adds another layer of Costs.

These Jadis things look rather Industrial, almost like something we'd find in a Sears Silverstone Stereo Console.

What is so darn compelling about these Amps?

Tony in Michigan

Charles Hansen's picture

I'm not sure there was much different about Jadis than any other imported audio product. As you note, shipping and an extra layer of profit for the importer adds to the cost of almost all imported products. The hadis amplifiers were expensive to build because of three major things - their massive transformers (both power and output, which were far larger than found on competing products), their meticulous point-to-point hand wiring done by French (not Chinese slave labor), and finally the polished chrome-plated steel chassis - also requiring a lot of hand labor.

For those with an eye for those details, they are as impressive (if not more so) than a 1" thick front panel. It's mostly just cultural differences that have us pay attention to certain details and notice the value therein, I believe. Victor Goldstein may have had a slightly higher distributor margin than typical, but not by much. He was based in New York and had to have a full-time technician of Chinese descent to repair and maintain them. (They had a lot of reliability issues!) I've forgotten his name, but after Mr. Goldstein stopped importing Jadis, his former technician (Da Hong? Ming Da? or something similar) used to both modify Jadis amps and also build his own amps from scratch. You will see the technician's name mentioned in the old TAS digest-sized issues when HP would review the Jadis amps.

The compelling thing was their sound. I think the JA-80 (single pair of output tubes) was more successful, and I heard some absolutely amazing sound from those amps. Hope that helps.

tonykaz's picture

Ayre takes "Digital Product of the Year"


Tony in Michigan

ps. thanks for your exotic amp comments. I've sold Tube gear and kinda agree with y'all on these things being what I call twitchy and prone to blowing up. phew ( keep u'r fingers crossed )

Having said that, my 1960 era Mac Tube Mono amp never blew itself up, nor did any of the Audible Illusions I sold ( thank god ).

I've heard horror stories about big Tube Amps.

I sold Electrocompaniet and didn't at-all miss the 'variables' of having to cope with tube gear.

I was once importing Tim De Paravicini's various tube Amps and didn't have a blow-up problem but they were waaaaaaaay over rated and didn't sound all that wonderful compared to a conrad-johnson Mv-75a. The Mv-45a was a sweet-hearted little charmer that I wish I still owned one of.

That gorgeous and charismatic sound quality you refer to is a rare bird. I had a local technician that would modify any used tube pre-amp he could get his hands on, his modified stuff would blow the doors 'Off' any of our Retail Showroom Products. His secrets were; especially fine resistors, expensive/exotic Caps. and Russian Tubes. His stuff typically had a short half-life.