Chris, nothing in the PCM1794's DS that I saw.
This kinda goes into what you're talking about, however:
http://www.ti.com/lit/an/sbaa150/sbaa150.pdf
This kinda goes into what you're talking about, however:
http://www.ti.com/lit/an/sbaa150/sbaa150.pdf
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I forget, someone cited one that was high Z ages ago.
I did a post in diyaudio, maybe even initiated it, when I was thinking about this stuff, in which I tabulated some results about output termination and the onset of non-monotonic behavior. I shudder to guess how long ago it was. As a woman in Waking Life says, I feel as if I have more time than ever, despite how obviously illogical that is.
I used the simplistic example of R-2R ladder networks and different resolutions, just to make the point. No pretty pictures, just some numbers iirc.
As far as the offset from a resistor, which will always be quieter than a current source [EDIT] (for the same available voltage), ADI does mention how quiet the PS better be.
Another application for synthetic "cooled" terminations? But one needs lotsa volts.
OK so TI is pushing their true-differential amps. Note that they still show the DAC outputs as (ideal) current sources, which they are (mostly) not.
Still not as good as enhancing feedback within/around topologies that are low input Z open-loop, IMO.
Hard to disagree that DACs aren't acting like idealized current sources, but we've got to start from somewhere, I suppose.
Got a link perchance to EUVL's (or, "deep purple" as I joke in my head) development of these designs?
The Zen Cen etc. thread in here, the Linear Audio article from a bit back. Let me see if I can dig it up, I think the first one has had some recent activity and I subscribe to it.
edit: latest post http://www.diyaudio.com/forums/digi...inimalistic-iv-converter-177.html#post4490160
I think Didden may have provided a free access to the piece in LA, not sure. Maybe it is in that Zen thread.
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I also started a thread I think called the Insense something or other, in which I repurposed some JFETs and reduced the input Z of the current conveyor a lot. One person's comment was he didn't see any advantage except the lower input Z. But based on a 1k input source impedance, I got 19dB less THD at a kHz. He was probably comparing the drive with 20k (Didden's Ap and a 20k resistor into the EUVL stage) to my 1k. Not exactly apples and apples.
With cascoding of BF862 parts, EUVL further reduced high frequency effects. That coupled with the error amp wrapped around the input looked quite promising.
With cascoding of BF862 parts, EUVL further reduced high frequency effects. That coupled with the error amp wrapped around the input looked quite promising.
That's interesting. Reminds me of experiment I did with speakers.
How did you discover it?
It has shown up in various guises in a number of circuits I've built/modded - most recently in a headphone amp I bought from Taobao - I've talked about it on my blog here : http://www.diyaudio.com/forums/blogs/abraxalito/1250-bargain-beaut-headphone-amp.html
The short version is - a TL072 feeding a discrete buffer was relatively heavily loaded in the stock unit by its own feedback resistor. Moving the resistor output side to the discrete buffer's output fixed it.
The short version is - a TL072 feeding a discrete buffer was relatively heavily loaded in the stock unit by its own feedback resistor. Moving the resistor output side to the discrete buffer's output fixed it.
Are there any existing vfa or cfa IC amps which would allow access internally to the Vas - before the OPS? Such that a seperate OPS could be used and no signal the IC OPS? Better yet also be able to disable the OPS?
THx-RNMarsh
THx-RNMarsh
From my faulty memory I think that pin 5 of the obsolete AD844 was an output before the OPS.
Yep, looks likely from here http://www.analog.com/media/en/technical-documentation/data-sheets/AD844.pdf
Silence. I have brought up similarly and get the same silence. He has not addressed a single concern I have ever brought up. His orthodoxy rules.
I am with you. But I have always been certain that what we can hear can be measured, just a matter of how, perhaps more a question of when, and now may not yet be when, not now but hopefully to come. The reliable technique has to be found, stimulus and capture. Until then, who are we to say what we can or cannot hear. What we hear is what eventually leads to rigourous investigation. Would anybody bother measuring distortion if it was inaudible?
I have only one complaint regarding IC op amps - over the years, I noticed that far too many of them lost too much ambience from otrherwise good recordings.
That said, I must add that was whyt I saw/heard in 2002, 13 years ago, when I last looked hard. I've lost touch with the op amp scene since then.
At that time, only AD op amps managed reasonable ambience in some of their fast op amps. By carefully comparing their offerings with others, I realized tht they differed from the others only by the fact that they offered not only respectable slew rates, but also (at the time) incredibly short settling times, and that not only up to the usual standard of 0.1%, but to 0.01%. I changed my factory supplied I/V op amp stage in my Yamaha CDX 993 CD player, an ubirious NHR op amp, for an AD 826, and I was rewarded with more detail and rather good ambience.
Moreover, I found out that the OPA 275 was also different to the majority in that same way, however, unlike the chips it replaced its settling time was "only" 6-7 times shorter, although not to the level of AD op amps.
Later on, I disliked the sound of BB 21xx opa mps to the point where I usually could tell if any were used in whatever, they had a shrill, shouty character of sound to my ears. Hardly perfect, but when you hear them like 6 out of 10 times, it does give you pause. Surely that's not supposed to be like that.
Then I bought the NAD C565 BEE, hich is chock full of them, and I didn't hear anything untowards, quite to the contrary, I bought it because of its excellent resolution and articulation, boxing well above its modest price class. Its heart is a Wolfson DAC. But it really shoved my own arguments back into my mouth. So, it's either that the signal path from the Wolfson DC is better suited to those op amos requirements, or somebody in NAD knew better how to implemet those op amps, or BB/TI had quitely improved them. Whatever, this is now some seriously good sound. Obivously, it's time to re-evaluate my general standards.
That said, I must add that was whyt I saw/heard in 2002, 13 years ago, when I last looked hard. I've lost touch with the op amp scene since then.
At that time, only AD op amps managed reasonable ambience in some of their fast op amps. By carefully comparing their offerings with others, I realized tht they differed from the others only by the fact that they offered not only respectable slew rates, but also (at the time) incredibly short settling times, and that not only up to the usual standard of 0.1%, but to 0.01%. I changed my factory supplied I/V op amp stage in my Yamaha CDX 993 CD player, an ubirious NHR op amp, for an AD 826, and I was rewarded with more detail and rather good ambience.
Moreover, I found out that the OPA 275 was also different to the majority in that same way, however, unlike the chips it replaced its settling time was "only" 6-7 times shorter, although not to the level of AD op amps.
Later on, I disliked the sound of BB 21xx opa mps to the point where I usually could tell if any were used in whatever, they had a shrill, shouty character of sound to my ears. Hardly perfect, but when you hear them like 6 out of 10 times, it does give you pause. Surely that's not supposed to be like that.
Then I bought the NAD C565 BEE, hich is chock full of them, and I didn't hear anything untowards, quite to the contrary, I bought it because of its excellent resolution and articulation, boxing well above its modest price class. Its heart is a Wolfson DAC. But it really shoved my own arguments back into my mouth. So, it's either that the signal path from the Wolfson DC is better suited to those op amos requirements, or somebody in NAD knew better how to implemet those op amps, or BB/TI had quitely improved them. Whatever, this is now some seriously good sound. Obivously, it's time to re-evaluate my general standards.
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