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Old 16th January 2013, 07:08 PM   #91
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Quote:
Originally Posted by abraxalito View Post

If all you want to make is something that works, why not copy the TI application circuit for that DAC? They use NE5534 which will suck sound-wise, but then that DAC's nothing special anyway so spending time optimizing for an S-D DAC isn't going to pay that many dividends in the end. Or by 'success' did you really mean sounding great? If so then the sooner you get away from your computer and behind a bench with an iron in hand, the better.
I doubt I can hear well enough to differentiate between superb and just good audio, so "sounding good to me" is enough of a goal. I can't hear higher than 10kHz and I have tinnitus so high end audio is pretty much lost on me.
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Old 16th January 2013, 11:55 PM   #92
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actually op amps designed, marketed for DSL service already are intended to operate with complex, wideband, "noise like" multitones in the QAM Mb modem signals

likewise medical imaging, ultrasound demands bandwidth, low distoriton to avoid wiping out contrast - and many superior performance analog op amps are made now for both these markets

and are speced to perform well with signals 1-2 decades above audio


I suspect some of them can even handle audio DAC output - if you incorporate any filtering at all

Last edited by jcx; 17th January 2013 at 12:01 AM.
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Old 17th January 2013, 12:14 AM   #93
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I tried the LME49710 as the I/V from the PCM1704 it wasn't good, the OPA627 was a bit better, but the LME49710 not used as an I/V is quite good, better than the OPA627 but neither as an I/V can touch the magic of the no global feedback of the Pedja Rogic's AD844, not even close.

Cheers George
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Old 17th January 2013, 01:58 AM   #94
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Quote:
Originally Posted by georgehifi View Post
I tried the LME49710 as the I/V from the PCM1704 it wasn't good, the OPA627 was a bit better, but the LME49710 not used as an I/V is quite good, better than the OPA627 but neither as an I/V can touch the magic of the no global feedback of the Pedja Rogic's AD844, not even close.

Cheers George
Did you perform any measurements? The OPA627AP and BP are very expensive.
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Old 17th January 2013, 02:43 AM   #95
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No Dirk, just how it/they sounded, and I did look on the scope for occilations and how the square waves looked and noise, and measure offsets and such to make sure nothing was going on that shouldn't have been, but no distortion measurements were done.
They (all feedback opamps) sound bad in comparison to the "feedback less AD844". Just just they all have a different type of bad and it comes down to which you don't dislike the most, I have found after listening to the AD844.


OK here goes some poetry to describe the sound, has to be done even for the measurement only freaks. If you don't like it don't read it I tried to refrane, but no longer.
It (the 844) gives you time to hear eveything, there seems to be a greater sens of space between the notes so nothing smears together, yet there is an abudance of detail and dynamics you didn't think possible, you get better fullness to each note even at lower volume settings, even cymbals seem to have more body. (forget about thinness and music being squeezed out at you) this doesn't happen with the AD844 at any volume setting. And I haven't even metioned the bass which is powerfull, tight and detailed and seems to go down another octave, yep there is some magic going on in the AD844 Pedja's way compared to all other opamps i/v's.

Cheers George
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Old 17th January 2013, 10:37 AM   #96
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Still looking for the last schematic for AD844 as an I/V for PCM1704.
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Old 17th January 2013, 11:14 AM   #97
Zoran is offline Zoran  Serbia
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this Vref should come to pin 3 of OP, and set the output to 0V
from pic on post #3
not @ pin 2
?
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Old 17th January 2013, 01:48 PM   #98
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The current feedback LM6181 is a possible replacement for the LME49710 in my IV converter. It models very well in Tina in my circuit. Other possibilities that I have not tried to model are:
LT1252
LT1217
LT1223
LT1227
these are all current feedback video amplifiers.
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Old 17th January 2013, 02:07 PM   #99
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Quote:
Originally Posted by merlin el mago View Post
Still looking for the last schematic for AD844 as an I/V for PCM1704.
I gave it here
Using the AD844 as an I/V

Cheers George
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Old 17th January 2013, 02:14 PM   #100
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Quote:
Originally Posted by georgehifi View Post
Here is what works great for my PCM1704, if your doing a sub for another I/V opamp, don't forget to disconnect the feedback loop around the old opamp.
And give thanks to Pedja Rogic for letting this out of the bag, as I think it would be hard pressed for even a discrete I/V to better the sound this can give. And kudos Barrie Gilbert for designing the AD844 and abraxilito for the dac dc offset nulling circuit
Cheers George
Quote:
Originally Posted by merlin el mago View Post
If I understood correctly instead the 15v psu + 2sk170 (2sk369) + VR1 + C1 can't be used, I must use the 2nd pic with the +-5V, right? with 20K preset I have to ajust 0VDC at pin 2 of AD844, right?
Quote:
Originally Posted by georgehifi View Post
I gave it here
Using the AD844 as an I/V

Cheers George
Thanks for letting me know George, could you confirm my question?

Cheers
Felipe
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