How do I connect a current output DAC to I/V stage single ended - diyAudio
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Old 22nd September 2010, 07:58 PM   #1
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Default How do I connect a current output DAC to I/V stage single ended

Hi,
I have an PCM1798 based DAC which has a passive I/V output stage and I am not very liked it. I want to try the new Zen JFET-based I/V stage and I have a (possibly very easy and dumb) question.

As you know the PCM1798 has differantial current outputs for each channel: IOUT(R/L)+ and IOUT(R/L)- . The Zen I/V has only one input. How can I connect these together to provide an unbalanced output?
I think I must connect the IOUT+ to Zen input and IOUT- to GND. Because I'm not very experienced these kind of circuits, I wanted to sure about this.

Thanks.
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Old 22nd September 2010, 08:44 PM   #2
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I did it like this, passive conversion. The DAC don't like large voltage swings, and the 50ohm resistors are a good match. The transformer is a Lundahl. Sounds pretty damn good

The output level is lower than redbook standard, but thats a good thing because you can crank the preamp volume, which means less wiper in the path.

Last edited by SemperFi; 22nd September 2010 at 08:46 PM. Reason: forgot the schematic:)
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Old 22nd September 2010, 08:47 PM   #3
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Like this that is:
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Old 22nd September 2010, 08:49 PM   #4
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Hmm, something is playing with me, cant seem to get the schem up. Perhaps I saved it in the wrong format....
Trying a jpeg.
Attached Images
File Type: jpg DACiv.JPG (7.9 KB, 333 views)
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Old 22nd September 2010, 10:40 PM   #5
jcx is offline jcx  United States
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or use 2 Zen, diff to single ended with xfmr: ( from What is the tradeoff to run a DAC single ended? )
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File Type: png zen_iv.png (21.9 KB, 320 views)

Last edited by jcx; 22nd September 2010 at 10:42 PM.
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Old 23rd September 2010, 12:27 PM   #6
Sandor is offline Sandor  Italy
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The should be almost no voltage between the drains of J1 and J3. Maybe the output capacitors may be omitted.
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Old 23rd September 2010, 05:30 PM   #7
DougL is offline DougL  United States
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Quote:
The should be almost no voltage between the drains of J1 and J3
True, but there is 30V between the drain of J1 and J2. While there are ways around it, juts removing the caps will not work.
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Last edited by DougL; 23rd September 2010 at 05:32 PM.
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Old 23rd September 2010, 06:12 PM   #8
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And why do u want all that in the signal path when one resistor per phase is aplenty?
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Old 25th September 2010, 05:03 AM   #9
qusp is offline qusp  Australia
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because 1 resistor is IMO and many other opinion, NOT PLENTY. you do not gain the best performance from the dac this way. current out dacs often prefer to operate into very low impedance and preferably with their outputs returned to a virtual ground biased to AVCC/2
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Old 25th September 2010, 05:44 AM   #10
Irakli is offline Irakli  United States
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Originally Posted by qusp View Post
because 1 resistor is IMO and many other opinion, NOT PLENTY. you do not gain the best performance from the dac this way. current out dacs often prefer to operate into very low impedance and preferably with their outputs returned to a virtual ground biased to AVCC/2
I agree about low impedance, but what is gained by biasing virtual ground to AVCC/2 ?
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