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Amir's TODO thread

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vitalii427

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I don't want to be a party pooper, but why does anyone want to see time spent measuring an AHB2? A full battery of tests has already been run on by a variety of people. Nothing new is going to be learned that is not already known. See https://www.stereophile.com/content/benchmark-media-systems-ahb2-power-amplifier-measurements and https://www.soundstagenetwork.com/i...hb2-stereo-mono-amplifier&catid=97&Itemid=154.
I saw this and other measurements. That is why I am interested in Amir’s measurements in the same conditions as a benchmark))
 
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A lot of people have been asking for cheap DACs to pair with Atom. Maybe re-measure D10 with new setup. Also, you have someone's DACMAGIC and also Cirrus Soundkey.
 
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I saw this and other measurements. That is why I am interested in Amir’s measurements in the same conditions as a benchmark))
i'm quite interested too, i must admit.

Also, would be nice to test the new Teac UD-505 which uses AK4497 in dual mono, both dac and amp sections.
 
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oh also the Alientek D8 and the SMSL Q5 pro for the entry level tier.
 

amirm

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I don't see the NAD D7050 on the list, even though Amir, I think you said you would test it…
Yes, the todo list is out of date and no longer maintained.
 

amirm

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I don't think you have posted the aune s6 yet, any chance you can still post the measurements?
Yeh, let me see if I can take a shot at it....
 

Stonetown

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Technics SE-M100 Power amplifier with built in DAC

Hello Amirm. How about testing vintage amplifiers? :) I have been using Technics SE-M100 since around 1990. I feel it is still very good compared to what we can get today. The "Class AA amplifier specifications (from the service manual available at hifiengine.com) are remarkable if looking at the distortion levels at 50mW and -26dB levels; 0,003 and 0,001%! Even the built in DAC is not bad. DAC is made up of 2 by 2 Burr-Brown PCM56P with to the output added 4 extra bits from the gate-array which is fed from the 20 bits 8fs Yamaha-IC SM5813 digital filter, makes the output very clean when I looked at it via simple ADC/spectrum analyzer (very clean up to the 100 dB of what I can see, and that was with 1 watt 1 kHz tone on power amplifier output, with the only visible harmonic at 3 kHz less than -95dB, using optical digital input)

Would be very interesting if you could get hands of this amp and test it. Both the pure analog part and also with the built in DAC. If I was living closer I would come by you with it (I am not so happy to post it).

I am attaching 2 pics from the service manual. Spec on one and other is showing the 4 bits added to the OP-amp on the top, to get the 20 bit resolution. Resolution still 16 bits on input but increased in the digital filter to 20 bits is for cleaning up the spectrum, of what I understand?

Wouldn't it be interesting to make measurements on this amp?

Cheers,
Per

Edit: For those who enjoys reading schematic diagrams I recommend to look deeper into this amplifiers circuit. It is really an interesting and advanced analog and digital circuit: The mentioned 20-bit system, The Class AA circuit with the voltage amplifier and bridge for the current drive stage. The volume control which for the DAC path is an amplifier gain adjustment instead of the normal attenuator potentiometer, to keep the DAC dynamic range for different audio listening levels all the way out to the speakers, etc.

The combination of the class A voltage amplifier for having low distortion at lower power levels, with the gain-adjustment of the amp for the digital chain, is clever to keep the low distortion figures and high dynamic range even when playing music at lower listening levels.

Skärmavbild 2019-03-24 kl. 08.16.47.png
Skärmavbild 2019-03-24 kl. 08.20.14.png
 
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gvl

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There is a hypothesis out there that coax SPDIF cables below certain length can cause quality degradation due to less than ideal impedance matching and reflections confusing SPDIF receivers. Some background: http://www.audiopolitan.com/blog/spdif-does-coaxial-digital-cable-length-matter/

Apparently Michael Ritter of Berkeley Audio Design made similar recommendations in the past.

Any chance we can put this theory to test?
 

amirm

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Wouldn't it be interesting to make measurements on this amp?
I thought I answered this but I guess I didn't. Yes, would love to measure it. So if anyone spots one on ebay and such, let me know.
 
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