本帖最后由 音乐之贼 于 2020-11-25 21:19 编辑
https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-meier-corda-jazz-amp.7197/
上面是ASR对 MEIER CORDA JAZZ 的测评，其实仔细看完多有回复楼层就知道
AMIRM根本就不懂JAZZ的特殊单端平衡输出电路设计，测量不准确。看到狼某某非常喜欢标榜和AMIRM相互验证，我就只能呵呵一笑。每个人都有自己的技术短板，同样都是国产货，狼某某的论坛免费测评，为什么帮某些品牌把关提高技术参数，而对一些品牌却发文打压？不是应该一视同仁的给出建议？帮助提高产品参数？还是说参数把关费用比较大，别人交不起？
就好比伟良的最新版DC300和这个NIAO耳放，你狼某某测出不好，给建议如何改进提高才更有说服力，发个图，贴个视频，一路黑到底，是一个技术教授所谓？更何况，就和AMIRM对JAZZ测评不准确一样，对狼某某的测评数据我也持观察态度。
13楼MRC01直接点明了有人不懂电路
Even though this amp has an unbalanced output jack, the ground carries a signal similar to a balanced output. It operates with differential signalling that Meier calls "active balanced ground driving" http://www.meier-audio.homepage.t-online.de/grounds.htm
Thus it should be tested as if it were balanced. Is it possible the poor distortion performance was caused by the test rig ignoring or grounding the ground output? This would drop half the signal and overdrive the amp's output stage.
96楼JAN MEIER 直接回复打脸AMIRM，后面AMIRM就怂了，不再回复技术问题，转而说JAN MEIER值得重视？
Dear friends,
the Jazz is one of my best selling amplifiers. It is loved by many and noone ever complained about its performance. Search the internet and you will find quite a few opinions/reviews.
So why is there such a discrepancy between its popularity and the measurement results as presented over here?
Before I explain you first have to know a little bit about the topology of the amp.
Inside the JAZZ the signal passes three stages. An input amplification stage with volume control, a passive network for the crossfeed and finally the output stage with two (LOW and HIGH) gain settings.
The topology of the input amplification stage is uncommon. It does not have a fixed amplification factor with a volume control (potentiometer) in front, but volume is set by changing the feedback resistance. The advantage is, that the gain-factor is decreased with lower volume settings and lower gain factors imply lower background noise. The resistance is varied by electronic switches that activate/deactivate various resistors.
The measurements present two major issues with the Jazz. First there is a higher than usual mains noise (humm) and secondly the amp starts to clip signal at a level that is much lower than most other amps.
As for the mains noise. The amp has a rather powerfull transformer and the enclosure is very slim. Although a toroidal transformer is used there always is a remaining magnetic field and this induces a signal into the traces of the audio signal. Simple physics.
A possible solution would have been to use a bigger enclosure, with the signal traces further apart from the transformer, or to use an external powersupply. However, I wanted the amp to be compact and for ecological reasons I don't like external supplies that are ON all the time.
A more modern solution would be to implement a switched powersupply, but at the time the Jazz was designed/developed these were not very common yet.
So the Jazz has a clearly higher humm level than e.g. the Corda Classic (which has a much larger enclosure) or the Corda Rock (which is a newer design with switched powersupply).
But is it really a problem?
Sure, compared to the random noise background the 60 Hz component is very high. One should however be aware that the sound pressure of a signal is proportional to both amplitude and frequency! And the frequency is very low.
Yes, the humm of the Jazz can be heard with sensitive headphones at very high volume settings. But if in this situation you would add a normal level input signal your ears would be blown instantaneously.
At normal listening levels humm is not a problem.
It should be noted that, in contrast to more conventional designs, the humm signal at the output decreases with lower volume settings. This is a result of the topology of the amp in which volume is set by changing feedback. Actually this can well be seen by the measurement results presented here.
At maximum volume the Jazz has one of the worsest SNR-ratios. But at a 50 mV output level the amp is 20 dB better than all other amps in the graph! It's a pity that the Amirm did not comment on this.
As for the clipping/distortion, why is this amp starting to do so at an output level that is much lower than would be expected by the supply voltages and the amplification elements used?
Well, the electronic switches used at the volume control do have a much lower supply voltage than the amplification elements. As soon as the output signal of the first amplification stages surpasses a certain threshold the signal will start to distort. In High gain, this distortion will start at around 3.5Vrms.
With a 2Vrms input signal this distortion starts at around 2 o'clock.
With a 200mVrms input signal (portable player) distortion will not be seen at all.
But again, is this really a problem?
Even with an ineffizient headphone like the HD800 (300 Ohm, 102dB at 1Vrms) an undistorted output of around 112 dB can be achieved. And that is a very unhealthy sound level:
https://www.noisehelp.com/noise-dose.html
With low impedance headphones undistorted sound levels are even much higher.
At normal listening levels the clipping of the amp is not a problem at all. Would it be, then you would have read about it in one of the many reviews found in the internet.
The "culprit" of the distortion thus is the electronic multiplexer switch at the volume control of the Jazz. Of course I could have used a conventional potentiometer instead, but the use of electronic switches allows for a much better channel balance.
As a side note: With normal music signals the implementation of the FF-technology reduces the output voltage at the first amplification stage by around 6..8 dB (depending on the frequency contents of the music). As a result undistorted sound levels are higher accordingly. So for true headbangers the FF-version of the JAZZ is recommended.
When you drive a system to its limits, then it will respond adversely.
And yes, the limits of the JAZZ are more strict than with most other amplifiers.
However, at normal listening levels the amp performs well. The proof is in its popularity and in the appreciation of those who own this amp.
Some comments to some comments:
" I find the graphics preminative and unattractive. "
Beauty is in the eye of the beholder.
"I am not one for detail as you can tell from my posts but come on: why is "designed" not capitalized? "
Seriously??
" Frequency response was flat enough to 20 kHz but then took a dive above 30 kHz"
Please be noted, that due to the concept of the volume control the frequency response depends on the volume setting. But even at the highest gain factor the -3dB point is still beyond 40 kHz.
Most headphones do not even get to 30 kHz.
And our ears ......
"They didn't even get the CE logo right."
With audio equipment the manufacturer has to guarantee that the devices he sells do fullfill the CE-requirements. And the JAZZ does, please be assured of that! The fact that I may not have printed the logo exactly according to design ....
" this amp is required by law to be CE-certified"
No, this is only required for very specific products like medical implants. With low voltage audio-products the manufacturer is responsible for fullfilling the CE-requirements. A certification is not mandatory (and never done by any of the smaller manufacturers, as otherwise you no longer could afford these products).
The JAZZ is very safe. I know well of the danger of electricity to the human body. By origin I'm a biomedical physicist and my PhD thesis was on the subject of neurostimulation. I worked 10 years as research project leader with a pacemaker company.
The CE-requirements are very strict. Do you ever wonder why certain companies from the US or Asia do not sell their headamps through a distributor in Europe?
" The unit is marked as "Designed by ... Germany" not "Built by ... in Germany" so you guess where it was built ..."
The amp was build by Shanling. Not the worst factory in the world. I don't make a secret about that.
Even high-end stuff like Quad and KEF are nowadays entirely produced in China.
" I would love to see a response from Jan Meier in this thread. But some of the comments are a little aggressive and that will most likely discourage him from doing so."
No, I don't mind a discussion as long as it is honest, fair and respectfull.
" You won't find in a german forum not a single one thread where someone expresses the smallest doubt about his amps"
Well, be assured that I never tell people what to write. My customers have to decide for themselves whether they want to write something and what they want to write. No fake news and no alternative facts here! I do not do in politics!
" His gear, always fine, always close to perfect german quality."
Being a Dutchman that's not really a compliment! ![]()
"Specs say: Maximum output 15V / 300 mA"
Oops! This is the spec for the JAZZ-FF at low measurement frequencies. With the FF-version the undistorted output level will increase below 1 kHz and reach its maximum at around 200 Hz.
Cheers
Jan Meier
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发表于 2020-11-25 12:14
太欢乐了
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