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Old 4th January 2012, 12:03 PM   #11
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Quote:
Originally Posted by SoNic_real_one View Post
beliving that all other electronics engineers (from TI, NatSemi, Wolfson, CL, Sony, Phillips, Toshiba, ESS, D&M and hundreds of other companies) are incapable to comprehend the wonders of resistors used as I/V is either just plain ignorance or megalomania.
This does rather look to be a red herring - who has such a belief?

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The truth is that it was tried and failed the tests...
Evidence?
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Old 4th January 2012, 12:35 PM   #12
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Originally Posted by DF96 View Post
The alternative is to use a real resistor - so-called passive I/V. The snag now is that you either need a very small resistor (less than 25 ohms?) and get some noise from the following preamp, or use a big resistor and suffer distortion (and, perhaps, clipping) from the DAC output stage (as it is not designed to produce voltage). So which do you prefer - noise or distortion? I suspect that some people who prefer passive I/V do so because they prefer mild distortion, because many published designs push the DAC well into its distortion region.
Interesting to check these distortion measurements with respect to I/V resistor values:
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Old 4th January 2012, 01:01 PM   #13
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Originally Posted by pieter t View Post
Interesting to check these distortion measurements with respect to I/V resistor values:
Digi Scoop 1
Yes, such distortion measurements are interesting, but not necessarily determinative of perceived sound quality by themselves. Else, we would all build or purchase only high-feedback solid-state amplification components.
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Old 4th January 2012, 01:05 PM   #14
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does anyone know the compliance voltage value for 1704?

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Old 4th January 2012, 01:22 PM   #15
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Originally Posted by Extreme_Boky View Post
does anyone know the compliance voltage value for 1704?

Boky
I believe that the 1704 compliance is limited by the output protection diodes becoming forward-biased, however, distortion starts to become objectionable before then. Even staying well within the protection diode conduction thresholds, the 1704 attempts to servo any D.C. output voltage to zero. In addition, it requires a large external capacitor to set the servo corner frequency low enough to not interfere with the A.C. signal. To my thinking, this is THE key issue surrounding the 1704 I/V implementation.

Passive I/V with the PCM1704 will best involve a low value resistor (perhaps, less than 10 ohms) and a commensurately high gain active output stage - essentially, a phono amplifier sans the RIAA equalizer.
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Old 4th January 2012, 01:28 PM   #16
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Quote:
Originally Posted by Ken Newton
Yes, such distortion measurements are interesting, but not necessarily determinative of perceived sound quality by themselves.
If the signal has visible clipping or peak compression then it is definitely distorted. I suppose some people might prefer this.
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Old 4th January 2012, 01:37 PM   #17
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Originally Posted by Ken Newton View Post
Passive I/V with the 1704 will best involve a low value resistor (perhaps, less than 10 ohms) and a commensurately high gain active output stage - essentially, a phono amplifier sans the RIAA equalizer.
I've recently tried AD603 with +/- 50mV compliance voltage (32dB gain) on the TDA1543 DAC with pleasing sonic results. It has the bonus of an in-built volume control too.

http://www.analog.com/static/importe...eets/AD603.pdf
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Old 4th January 2012, 01:56 PM   #18
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Originally Posted by DF96 View Post
If the signal has visible clipping or peak compression then it is definitely distorted. I suppose some people might prefer this.
Yes, distortion visible to the naked eye in a time-domain plot is severe. Severe distortion is objectionable, no debate from me on that. The debate begins for THD beneath a gross level. My experience is that increasingly lower THD measurements alone often do not correlate with improvements in perceived sound quality. In fact, there often seems to be a negative correlation between perceived sound quality and vanishingly low THD. This phenomena is not only apparent with DACs, but has been apparent with amplification since the Japanese solid-state receiver THD spec. war of the late 70's early 80's.
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Old 4th January 2012, 02:03 PM   #19
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Originally Posted by abraxalito View Post
I've recently tried AD603 with +/- 50mV compliance voltage (32dB gain) on the TDA1543 DAC with pleasing sonic results. It has the bonus of an in-built volume control too.

http://www.analog.com/static/importe...eets/AD603.pdf
An interesting device. I'll have to take a closer look at it.
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Old 4th January 2012, 02:08 PM   #20
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I've moved on to balanced I/V stages now for which the AD605 is more suitable:

http://www.analog.com/static/importe...eets/AD605.pdf

Owing to the limited (5V) supply voltage it can't deliver the standard CD 2VRMS in unbalanced.
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