Why do we need I/V stage for AD1865 - diyAudio
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Old 12th April 2013, 05:59 AM   #1
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Default Why do we need I/V stage for AD1865

I observed nearly all AD1865 DAC has an I/V stage. Since AD1865 has Vout, why do we still need an I/V stage?
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Old 12th April 2013, 06:39 AM   #2
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Not all AD1865 DAC's have an I/V...but I guess a buffer will be an advantage.

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Old 12th April 2013, 07:08 AM   #3
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probably because external I/V converters sound better than the I/V converter inside the AD1865.
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Old 12th April 2013, 10:56 AM   #4
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Does anyone experienced using the Vout of AD1865?
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Old 12th April 2013, 12:24 PM   #5
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I have designed and built AD1865 based DACs in Vout mode, and in passive I/V curret output mode. My experience is that while much depends on the implementation of the modes, I obtained MUCH better sound from the current outputs via passive I/V. I've used passive I/V resistor values as large as 330R without aubible distortion, but find that lower value resistors give a subjectively more focused and organized kind of sound that's particularly obvious in the bass. I currently use 75R, but want to try 50R in the near future. Follow this hyperlink for further detail. AD1865 w/6DJ8 SRPP - mod suggestions

Another intriguing option, which I haven't yet had oportunity to try myself, is proposed by 'Vandenberg' on his homepage. It intrigues me because it follows a basic topology a number of us have found to enable outstanding sound with current output DACs. The basic topology is: low value passive I/V resistor, followed by a passive low pass filter, followed by a medium gain active voltage amplification stage. Vandenberg implements that topology with the AD1865 by re-purposing the AD1865's internal op-amp as a voltage amplifier (instead of transimpedance amplifier, as intended). This is easily done by inserting two external resistors in the op-amps's feedback loop via it's connection pins.

http://www.diyaudio.com/forums/attac...ad1865-diy.doc

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Last edited by Ken Newton; 12th April 2013 at 12:28 PM.
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Old 12th April 2013, 12:34 PM   #6
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Ken, thank you very much for your input.
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Old 25th April 2013, 10:24 AM   #7
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I've just ordered a pcb to try this circuit which has a clever implementation of v-out, will report back ASAP.

AD1865 based audio DAC with I2S input and voltage output
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Old 25th April 2013, 12:42 PM   #8
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Quote:
Originally Posted by lordearl View Post
I've just ordered a pcb to try this circuit which has a clever implementation of v-out, will report back ASAP.

AD1865 based audio DAC with I2S input and voltage output
Hi, Earl,

It appears that the v-out circuit shown in the schematic you hyperlinked is simply the datasheet recommended implementation. In other words, a typical feedback based transimpedance amplifier. Have I overlooked something?
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Old 25th April 2013, 08:12 PM   #9
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Hi Ken, yes you are correct - the output is the standard implementation. The 'clever' part is the i2s functionality and correction of the shift register.

In fact, do you think it is possible to take the output from pins 8 and 17 of the dac and get i-out?
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Old 25th April 2013, 08:55 PM   #10
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Originally Posted by lordearl View Post
...In fact, do you think it is possible to take the output from pins 8 and 17 of the dac and get i-out?
I-out is directly available via pins 4 and 21. The AD1865 may be configured to operate in either V-out or I-out mode. I don't find the V-out mode to sound particularly pleasing, but that's only my opinion.

Also, in my experience, there is no perceptible benefit of correcting the 11uS linear phase interchannel delay, at least when listening to loudspeakers. All of those shift register chips may increase jitter though.
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