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New i/v stage in town
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Old 10th April 2019, 12:09 PM   #1
dreamth is offline dreamth  Romania
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Default New i/v stage in town

As i found some more time to perfect my i/v stage started here
Best way to mod cheap cd-players-enhancing the noise
I thought that it now deserves an entirely new topic because it started to look really promising.
I started this exploration on a tda1543 and when i wanted to find the best op-amp for an 8x upsampling dac based on pcm1701 which should have about 0.5...1ma max IOUT , i simply found out that there aren't many choices out there for a good op amp to do the job because you need very low voltage and current noise along with good output drive and fairly good slew rate to deal with the ultrasonic trash.

I used the same idea used in Denon dcd1560(my best cd-player) of shunting the iout with a capacitor but i wanted to do it the right way, so that both the dac and the op-amp would harmoniously fight each other.
I had to deal with some lack of knowledge about how to sim a real dac output and make the simulator tell some beautiful lies, but now i know the WAY!
Attached Images
File Type: png ivpcm17011.png (78.8 KB, 567 views)
File Type: png ivpcm17012.png (66.4 KB, 563 views)
File Type: png ivpcm17013.png (79.4 KB, 554 views)
File Type: png pcm17014.png (72.6 KB, 549 views)
File Type: png ivpcm17015.png (77.3 KB, 538 views)
File Type: png pcm17016.png (74.2 KB, 44 views)
File Type: png ivpcm17017.png (87.9 KB, 54 views)
File Type: png ivpcm17018.png (84.6 KB, 53 views)
File Type: png ivpcm17019.png (88.4 KB, 51 views)
File Type: png ivpcm170110.png (85.4 KB, 70 views)
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Old 10th April 2019, 01:53 PM   #2
Terry Demol is offline Terry Demol  Australia
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The numbers look impressive but - you forgot to include OP impedance of the DAC.
I'm not sure what the TDA1541 is, the PCM63 is less than 1k, the 1702 is a few k.
Once you include some OP Z for the DAC and sim at say 10kHz, the numbers will look more real.

T
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Old 10th April 2019, 02:14 PM   #3
dreamth is offline dreamth  Romania
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I just realized that i have the wrong bias too, as i got the old sim for tda1543 which was biased at 2v ...that's not a problem though, i can reference it to the negative V.

I'll try doing this the right way...but at least the last numbers with the same "no zout" were 85 db for H2 max.
Now...how the hell do i sim the dac z out? Just by making the voltage source series resistance 1k doesn't look realistic.I get the same results...
Attached Images
File Type: png ivpcm1701true1.png (88.0 KB, 84 views)

Last edited by dreamth; 10th April 2019 at 02:34 PM.
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Old 10th April 2019, 03:40 PM   #4
dreamth is offline dreamth  Romania
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Could somebody help me with how to sim the dac output impedance the right way?I simply don't know...Is it just by making the series resistor of the voltage source or by adding a series resistor to the current output?
Attached Images
File Type: png ivpcm1701true1.png (88.0 KB, 65 views)
File Type: png ivpcm1701true2.png (82.8 KB, 32 views)
File Type: png ivpcm1701true3.png (89.5 KB, 19 views)
File Type: png ivpcm1701true4.png (92.2 KB, 18 views)
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Old 10th April 2019, 03:50 PM   #5
smms73 is offline smms73  Europe
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Add a 1k resistor in serie to a voltage source and delete the current sources. I do like this to simulate a es9018
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File Type: png in.png (3.8 KB, 33 views)
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Old 10th April 2019, 04:19 PM   #6
dreamth is offline dreamth  Romania
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I just realized a huge problem...the way the transistors are biased in ground referenced circuits is completely wrong for the real circuit.I'm working on this first

Last edited by dreamth; 10th April 2019 at 04:31 PM.
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Old 10th April 2019, 06:12 PM   #7
dreamth is offline dreamth  Romania
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Quote:
Originally Posted by smms73 View Post
Add a 1k resistor in serie to a voltage source and delete the current sources. I do like this to simulate a es9018
Before i play with your version of dac out i just wanted to make some more sims playing with the trz bias.I have a few versions with -140db(0.5ma in-pcm1701), 120db(4ma in-tda1541), then some versions aiming at only 100db .I also increased the input capacitor to 1nF.it might work better for the real thing and then i would probably need less than 100pf for the feedback.
Attached Images
File Type: png ivpcm1701x-140db.png (84.3 KB, 40 views)
File Type: png ivtda1541x-120db.png (87.3 KB, 25 views)
File Type: png ivtda1541x100db.png (86.1 KB, 15 views)
File Type: png ivpcm1701x120db.png (84.6 KB, 14 views)
File Type: png ivpcm1701x100db.png (85.0 KB, 17 views)

Last edited by dreamth; 10th April 2019 at 06:20 PM.
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Old 10th April 2019, 07:09 PM   #8
dreamth is offline dreamth  Romania
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I used the resistor + voltage source.At 1khz the results aren't far from my voltage-current source version, at -110...-130db as they are identical at 10khz, at about -40..50db for the second and third hamonic, but i wonder who's going to hear it...
Attached Images
File Type: png pcm1701xxx.png (87.1 KB, 31 views)
File Type: png ivtdapcmess.png (89.6 KB, 28 views)
File Type: png iv10khz1ma.png (98.1 KB, 15 views)
File Type: png iv10khz4ma.png (91.5 KB, 15 views)
File Type: png iv10khz4max.png (96.0 KB, 19 views)
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Old 10th April 2019, 08:07 PM   #9
dreamth is offline dreamth  Romania
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Anyway, i had no intention of using lt1115 for i/v...it's a bit too slow for this application, but it was readily available in LtSpice component library.I mainly aimed at using both sections of double op-amps when present in vintage digital equipment.
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Old 11th April 2019, 03:05 AM   #10
dreamth is offline dreamth  Romania
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just some more fun:
Attached Images
File Type: png ivpcm1792.png (89.4 KB, 56 views)
File Type: png ivpcm17922.png (90.0 KB, 59 views)

Last edited by dreamth; 11th April 2019 at 03:20 AM.
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