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Old 6th November 2012, 06:48 PM   #571
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You are absolutely right that one can use the 16 DACs inside the ESS9018 for 8 channels but using paralleled DACs gives better performance (THD and noise wise). Many commercial high end audio companies use DACs paralleled be it PCM1704, or PCM1794, or ESS9018 or the TDA-series.

Using the DAC in mono mode gives the advantage that each ESS9018 chip is separate for each channel. Also often used by high end audo companies.

< the input for the I/V converter for the ESS9018 will be less than 1 ohm,

Great!



/S

Quote:
Originally Posted by smms73 View Post
staccatiss thanks for the list of opamps, and do not worry, the input for the I/V converter for the ESS9018 will be less than 1 ohm,
Just one question regarding the ess9018 . Why use all the 8 output in parallel? one can use only one output per channel and shunt the remaining 6. anyone know the reason?
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Old 6th November 2012, 07:02 PM   #572
MiiB is offline MiiB  Denmark
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Hats off.. I did not see it the way...you get both... a good current source and the possibility to mirror in the servo current...What a good tool thanks.

/M
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Old 6th November 2012, 08:12 PM   #573
smms73 is offline smms73  Portugal
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staccatiss I know that. my now deceased 16 years old cd player uses four tda1541a.
paralleling dac gives in theory less error, but is there a great difference with the new dacs like pcm1794 or ess9018? one way or another i will design for 8 dacs per channel.
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Old 6th November 2012, 08:15 PM   #574
smms73 is offline smms73  Portugal
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MiiB im glad that you agree that this is a good solution.
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Old 6th November 2012, 09:10 PM   #575
Shinja is offline Shinja  Japan
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Quote:
Originally Posted by smms73 View Post
Why use all the 8 output in parallel?
to obtain insanely high SNR...despite nothing improve THD at fullscale.

Last edited by Shinja; 6th November 2012 at 09:14 PM.
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Old 6th November 2012, 09:38 PM   #576
smms73 is offline smms73  Portugal
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Yes, but is a burden for the I/V stage, but as everithing in live is a compromise.
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Old 7th November 2012, 12:57 AM   #577
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Quote:
Originally Posted by smms73 View Post
The Dc servo will be one of this, the first is recommended by Bob Cordell and only use 1 capacitor. Can you guys recommend a jfet opamp with good dc precision for this, no need for low noise.
TL052 is a good jfet opamp.
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Old 7th November 2012, 03:45 PM   #578
smms73 is offline smms73  Portugal
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tl052 is a possibility. But i will use for now OPA2134, of course others opamp can be use.
I have test the circuit with five OPA2134 , 2 of them give output of 200uV, 2 give less than 100uV and one give 800uV.

There are a lot of very high precision low voltage opamp out there, like for exemple the
max4238 it is a cmos opamp it cost less than 1 euro and has 0.1uV offset voltage , 10nV/Cº Drift , 1 pA input bias current. the maximum P.S. voltage is 5V.
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Old 7th November 2012, 04:00 PM   #579
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by staccatiss View Post

A servo should only take care of the last few mV of DC offset for temperature drift and component drift over time. The major DC offset fix should be a trim pot somewhere.

/S
There is no need for a trimmer, the output D.C. voltage of the I/V converter is always the input offset voltage of the servo opamp, i have inbalance the input with 8ma on purpose and the D.C. output stay in the 100uV. i have also made a temperature test, and there was no variation at 50Cº.
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Old 7th November 2012, 04:15 PM   #580
smms73 is offline smms73  Portugal
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The servo that i test is this one, i use a 1Meg in R4 as staccatiss suggested but there is no difference, but i will leave it like that. the next image are the I/V converter noise floor with servo, the second image is without servo, the third is emu1212m alone. The last one is the power supply noise alone.
Attached Images
File Type: png servo.png (11.1 KB, 260 views)
File Type: png noise_servo.PNG (77.0 KB, 253 views)
File Type: png noise.PNG (75.2 KB, 245 views)
File Type: png emu1212m_noise.PNG (83.3 KB, 224 views)
File Type: png ps_pos_noise.PNG (87.4 KB, 217 views)
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