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Old 20th February 2010, 01:43 AM   #1
a.wayne is offline a.wayne  United States
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Default The NEM AI-50

Interesting amplifier.... what's with all the trannies ?

6moons audio reviews: NEM Ai-50
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Old 21st February 2010, 08:14 PM   #2
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Hi,

I happen to know Andrejs, he came to visit Kaunas a few times and brought that amp with him, so I had a chance to hear the thing on a few occasions. It is quite a beast, and with practically zero coloration of the sound in any direction I could notice. The many transformers are needed because of the design principle utilized. This was explained in the 6moons article better than I have the understanding to expand upon, but from what Andrejs told me, each transformer is custom made to the exact spec it will be used in the circuitry. (Not merely custom wound, but measured with an oscilloscope until it is perfect). The amp runs surprisingly cool. And it weighs like a tank. It has a remote controlled discrete volume control built in. I would be willing to bet it is the best value for the money out there. (I mean, they compared it to a Luxman which costs 10 times as much). Andrejs tells me that even Luxman didn't go to the extent that this NEM amp takes the PS.

If I can, I will gladly mediate a little bit here since Andrejs speaks German with me (we Skype often: he lives in Münster, Germany, and I live in Kaunas, Lithuania). So if there's anything I can answer regarding the design, I'd be glad to.

Louis Motek
Kaunas, Lithuania
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Old 22nd February 2010, 02:52 AM   #3
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Hi all,


My name is Sergey Rubtsov, the designer of NEM. We made this amp.
I will be glad to answer Your technical questions.

Sergey

Last edited by NEMaudio; 22nd February 2010 at 03:00 AM.
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Old 22nd February 2010, 03:47 AM   #4
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Welcome to the forum Sergey. The pictures on 6moons show a stunning amplifier -- especially with the top off

The design concept is very appealing to me as well.

dave
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Old 22nd February 2010, 04:17 AM   #5
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Thanks, Dave.
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Old 31st March 2010, 02:14 AM   #6
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Default Hello NEM audio

I've read the review on 6M with great interest, and I have a couple of questions.

What is the rise time for the amp?

In its THD plot, what flares out most: even or odd order harmonics?

Is the frequency range limited by you or is it the max the amp capable of?

How much AC filtration/regulation is needed?

Thanks
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Old 1st April 2010, 11:12 AM   #7
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Hi!

Sigmal rate is 10V/microsec and is restricted by the parameters of interstage transformer. We do not use feedbacks in the amplifier, and thus SR determines the upper frequency at nominal power, which is 80 kHz -3 dB.

The frequency range depends almost on interstage transformer. We specially design the transformer such that the wide bandwidth is not the primary goal, as in our opinion the transformers with middle frequency (sqrt(Fb*Ff)) 400-600 hz are the most musical.
The low frequency limit is 2.5 Hz - 3 dB.


The most important goal in our transformer design are the efficiency and low electric and magnetic losses, so the primary winding has typical DC resistance less than 3-5% of internal impedance of driving tube, and the core has big cross-section area, 16 sq.cm.

The number and spectrum of harmonics is determined almost only by the driver tube, typically it is less than 0.2%. I have attached the pic with spectrum of harmonics.

In general, there is no need for AC voltage filtration/stabilization, if AC voltage is in the range of +/- 5%. If AC power is dirty, this must be solved in each particular case.

Sergey.
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Old 1st April 2010, 11:55 AM   #8
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spectrum
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File Type: jpg 12W 8 Ohm.jpg (223.3 KB, 566 views)
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Old 1st April 2010, 06:19 PM   #9
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Thank you Sergey
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Old 5th April 2010, 01:36 AM   #10
a.wayne is offline a.wayne  United States
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Wow i can't believe i had missed following up on this ...,


Hello Sergey , fantastic bit of amplifier, my question ?


Are you saying that PS filtration is not important due to each stage having it's own transformer ?

Regards,
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