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Old 20th September 2013, 09:41 PM   #601
impuls is offline impuls  Yugoslavia
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I have modified cd player with PCM63P-KY. After many changes i have come to very precise relaxed sound. Maybe a little sterile. Then I tried 3 stacked AD844 and the result is:
- the sound is not as accurate
- all tones are slightly rounded
- middle tones is much more comfortable
- AD844 and PCM63 are warmer

I do not know if this is what pleases me but I really miss the exact sound that I had.
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Old 21st September 2013, 12:32 AM   #602
dacen is offline dacen  Norway
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Maybe these speakers are very revealing. I can actually hear the pianist´s activity on the pedals of his piano and the breathing of James Galway playing his flute. I have had these for over twenty years and I have never heard them sounding so realistic. I have to add that my DAC has the master clock and the players are modified to be slaved to this master clock via fiber optic link ST connection. So the clock generated from the SPDIF data stream is not used as a master clock in the DAC.
https://picasaweb.google.com/tsundsd...56458436717122

Last edited by dacen; 21st September 2013 at 12:46 AM.
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Old 21st September 2013, 03:41 AM   #603
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Quote:
Originally Posted by impuls View Post
I have modified cd player with PCM63P-KY. After many changes i have come to very precise relaxed sound. Maybe a little sterile. Then I tried 3 stacked AD844 and the result is:
- the sound is not as accurate
- all tones are slightly rounded
- middle tones is much more comfortable
- AD844 and PCM63 are warmer

I do not know if this is what pleases me but I really miss the exact sound that I had.
I think that maybe you are hearing what I first thought ( Using the AD844 as an I/V ) when going from double to tripple. I thought maybe the double had a little more leading edge than the tripple, but now after living with the tripple, it maybe just less leading edge distortion, when I try 4 stack I'll get a better idea.

Cheers George
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Old 21st September 2013, 07:24 AM   #604
impuls is offline impuls  Yugoslavia
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I think the more parallel operational amplifier there is a slight delay in the signal between them and the edge of tones are losing and gets a holographic sound effect. Everyone who listened said the better. For me it sounds more like all round system, like Revox or Bang Olufsen.
I had Revox B242 first thing I did was reduce capacity between pins 5 and 8 NE5534 from 47pF to 5pF. I love it when the sound is so accurate that I hear even the slightest change in the system in terms of cables, connectors.

Last edited by impuls; 21st September 2013 at 07:42 AM.
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Old 21st September 2013, 08:35 AM   #605
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Hi impuls, my thoughts exactly about paralleling devices. I too lost pin point imaging when i paralleled 844. Same thing again with tda1543 that ive noticed for a while now. I think with 844 the benefits outweigh the con. And this smudging effect is rather pleasant if you didn't know what to listen for
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Old 21st September 2013, 09:17 AM   #606
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With the PCM1704 (+-1.2mA) dacs on my system (big esl/hybrid based) not the Wilson Halcro system that we've been doing the A/B's on. I may favour the 2 stack, one day I will go back and see what it sounds like again.

Cheers George
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Old 21st September 2013, 12:16 PM   #607
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I once simulated the AD844 some years ago. It showed excellent performance, so long as the transistors were very closely matched. Relatively small transistor parameter mismatch produced relatively significant increases in THD,, which is not surprising in a complementary topology used open-loop. That's what is so nice about the AD844 IC, the integrated transistors on the monolithic chip are apparently well matched.

I feel that a discrete, high quiescent current version can perform better if pains are taken to match and thermally couple the transistors, which may prove problematic. This suggests to me the use of monolithic transistor arrays to build a diy implementation.
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Old 21st September 2013, 12:56 PM   #608
smms73 is online now smms73  Portugal
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Quote:
Originally Posted by georgehifi View Post
The AD1865 dac can only give out 1mA and skouliki found a difference with 3 stack, so this means to me that it not a current starvation thing. I think it's the lowering of input impedance that were hearing.

Cheers George
Today I have simulate the AD844, and to have the 50 ohms of input impedance the 844 specifies , the quiescent current in the input stage had to be only 300uA .
then I test the distortion with an input signal of 0.6ma at 1khz to simulate a pcm1704 at -6db full scale, the distortion was 0.12% .
With 3x AD844 in parallel the distortion goes down to 0.008%.

So, even that the AD844 has only less than 500uA of quiescent current in the input stage, the distortion is not to high, due to the complementary topology of the chip , that cancells at the output the huge quantity of pair harmonics that are created in the input.

the AD1865 also benefits from paralleling 844.

In the image is possible to see at green the current at emiter of Q4 and Q14 and at red the output current. the distortion of the input current is so huge that can be easily seen. the upper graph is the input impedance of the circuit (50 ohms).

So, yes, the 844 have a current starvation problem.
Increasing the quiescent current will also bring the input impedance down, at 10mA the input impedance is less than 2 ohms. So there is something to gain in doing a discrete circuit with a increase quiescent current.


I have seen the s3tup's discrete 844 (thanks george), but there is a lot of things that I would do different, so I will do my one version.
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Old 21st September 2013, 08:59 PM   #609
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Great work Sergio, how can we up the quiescent current on the 844's input. Is it what Pedja's circuit has here and is it enough. Using the AD844 as an I/V

Cheers George
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Last edited by georgehifi; 21st September 2013 at 09:03 PM.
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Old 21st September 2013, 10:16 PM   #610
smms73 is online now smms73  Portugal
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Yes George, the Pedja's circuit should work for pcm1704, but it will have a dc offset at the output , the best is to inject a current in the pin 2 and the same current in pin 5 , the circuit in the image should be better , as there is no offset voltage at the output , R14 can be a trimer, to regulate the output voltage offset . In simulation the input impedance from the AD844 falls to 6 ohms, the distortion is 0.01% mainly 2º harmonic, using this technique the AD844 loses the complementary characteristic.
The sound from this technique should please the tube lovers.

If someone wants to use this , please be carefull as I never try this with a real AD844 , and it can damage the 844 chip , so do not connect the dac chip until you have certain that everything works fine , and the 844 does not overheat. I think that every thing should work o.k. , but until we try we never know.
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