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Old 12th November 2012, 07:51 PM   #611
Telstar is offline Telstar  Italy
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Originally Posted by smms73 View Post
Yesterday i have finished the prototype of the I/V converter . And made some tests.
I must say, that i am very happy with the results.
As predicted the distortion is very low , and i can not measure it with the equipment that i have (emu1212m) better than 0.0003%. Anyway i post here a picture of 2,8 Volts rms output in 1kohm. 8ma p-p.
Gz
(I'm reading all thread, very educative)
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Old 12th November 2012, 08:21 PM   #612
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I will apreciate if you guys tell me the requirements, (as you did) for DAC´s that you guys like. I want to try different chip
PCM1704 please
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Old 13th November 2012, 02:59 PM   #613
smms73 is offline smms73  Portugal
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Originally Posted by Joachim Gerhard View Post
I find it just so sad that amp designers do not talk much to speaker designers. I think we should take the interface problems more serious.
I find this topic very, very interesting, and I have some ideas. I hope we can discuss that in a near future, just let me finish the pcb for this project.
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Old 13th November 2012, 03:11 PM   #614
smms73 is offline smms73  Portugal
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Originally Posted by Telstar View Post
Gz
(I'm reading all thread, very educative)
Glad i am not the only one that have learn something .

Telstar to use pcm1704 only need to change the output resistance and capacitor to have 1 volt rms at output you need 1kohm in parallel with 1.8nf .
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Old 13th November 2012, 03:34 PM   #615
Telstar is offline Telstar  Italy
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1V rms output is too low, I need at least 2V. Output impedance would be 2k, right?
Maybe some of the 1704 aficionados will post some mod of your circuit to suit this dac better.
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Old 13th November 2012, 04:04 PM   #616
smms73 is offline smms73  Portugal
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yes, 2k and 870p .

about the mods , i am always open to suggestions.
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Old 13th November 2012, 04:22 PM   #617
smms73 is offline smms73  Portugal
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Originally Posted by staccatiss View Post
Depending on the OPamp used, and the individual spread amongst this OPamp, using R4 will balance out the input bias currents optimally for minimum DC offset.

Not often seen but sometimes used when lowest possible DC offset is wanted.


/S
Yes you right , for some opamp that has a high bias current, but for opa2134 for example that has 5pA of bias current the voltage in 1 Meg is 5uV . so it is better to not have the resistance (less noise) i am sure you agree with me.
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Old 13th November 2012, 08:03 PM   #618
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Originally Posted by Telstar View Post
PCM1704 please
Yes PCM1704/02 me too please to help they have +/- 1.2mA at 1kohm, if we then could get 2v out I'll be happy.

Cheers George
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Old 13th November 2012, 08:27 PM   #619
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PCM1704 too please.
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Old 13th November 2012, 09:50 PM   #620
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the 1704 is "easy"... gain is changed by the output resistor, Sergio already gave some suggested values. If you then need more output, scale the resistor and cap accordingly. for low output DAC's it could be beneficial to use an output buffer, like the simple B1 or similar.

As the PCM1704 and also the TDA1541 operates +/- No counter-current is needed at the input.
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