Using the AD844 as an I/V - Page 8

qusp · 15th January 2013, 01:33 AM

dont have time now, havent read them for years. i'll look into that when I refresh on his articles soon, looking to do a layout of the recent shunt version.

but another point I will make is that Walt is not the only one to have had trouble with AD797 at low or unity gain. its one of the reasons its been labelled as a somewhat cranky opamp. maybe its simply that running at low or unity gain accentuates issues with problem PCB layouts that would otherwise be fixed with higher gain.

abraxalito · 15th January 2013, 01:36 AM

Yes Walt had stability issues, that's what Jan was talking about, but he didn't abandon the AD797 in that design until he came up against RF issues. Only then did he chuck out the part in favour of AD825.

qusp · 15th January 2013, 01:43 AM

Quote:

Originally Posted by abraxalito

Yes Walt had stability issues, that's what Jan was talking about, but he didn't abandon the AD797 in that design until he came up against RF issues. Only then did he chuck out the part in favour of AD825.

huh? now your just being silly, just because there was another issue in addition to the stability that was the final straw, doesnt mean that stability was not an issue, or even the major issue. I'm not saying it was or wasnt, its been too long for me to remember, but why seemingly argue that stability was not an issue?

anyway thanks for the reminder, its always good re-reading articles from these guys as experience grows, further things usually click into place.

abraxalito · 15th January 2013, 02:02 AM

Stability wasn't the issue that killed the AD797 in that design - Walt was happy that it was resolved enough to continue to keep the AD797 in that reg design. You think Mr Jung would run with a design that he didn't consider good enough to publish and recommend others to copy when they needed a reg? To me that says stability wasn't a significant issue in that design.

EUVL · 03:36 AM

Looks like George is happy with Zin = 65 ohm for his 1704 after all.
But I have the SEN, and the AD844.

Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

Patrick

qusp · 15th January 2013, 03:27 AM

yeah its too high for ESS or I would try it

EUVL · 15th January 2013, 03:38 AM

Too high for me even for the 1704.
But I know some people has tried the 1704 with 22R passive IV followed by tube stage.
So maybe 3x 844 in parallel will do ....

I still prefer my SEN, by far. But then I am biased.

Patrick

georgehifi · 15th January 2013, 06:30 AM

Input Z for the AD844 is 50ohm typical, , and happy with it is an understatment, it's a game changer as far as being compared to the normal highend opamps with feedback.
This AD844 when used without global feedback and even with it's own output buffer has made me feel that all other opamp based I/V's are seriously flawed, and I don't think I have it at it's best yet either.
Someone said it needs to be biased higher than it's quiescent current of 6.5mA, but correct me if I'm wrong but the PCM1704 can only give +-1.2mA at full swing 0dbf.
But maybe they meant with the TDA1541 which gives out a much higher than that.

Cheers George

EUVL · 15th January 2013, 08:51 AM

We have eventually built the AD844 discrete using BC550 / BC560 (see the link above) ourselves to get to the low Zin of <10R.
I still prefer the SEN in an A-B test.

Patrick

merlin el mago · 15th January 2013, 11:54 AM

What about this IV for PCM1704?

15th January 2013, 01:36 AM	#72
abraxalito diyAudio Member Join Date: Sep 2007 Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though... Blog Entries: 62	Yes Walt had stability issues, that's what Jan was talking about, but he didn't abandon the AD797 in that design until he came up against RF issues. Only then did he chuck out the part in favour of AD825. __________________ When a measure becomes a target, it ceases to be a good measure. C.A.E. Goodhart

15th January 2013, 02:02 AM	#74
abraxalito diyAudio Member Join Date: Sep 2007 Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though... Blog Entries: 62	Stability wasn't the issue that killed the AD797 in that design - Walt was happy that it was resolved enough to continue to keep the AD797 in that reg design. You think Mr Jung would run with a design that he didn't consider good enough to publish and recommend others to copy when they needed a reg? To me that says stability wasn't a significant issue in that design. __________________ When a measure becomes a target, it ceases to be a good measure. C.A.E. Goodhart

15th January 2013, 03:23 AM	#75
EUVL diyAudio Member Join Date: Oct 2003	Looks like George is happy with Zin = 65 ohm for his 1704 after all. But I have the SEN, and the AD844. Zen -> Cen -> Sen, evolution of a minimalistic IV Converter Patrick __________________ xen-audio.com Last edited by EUVL; 15th January 2013 at 03:36 AM.

15th January 2013, 03:38 AM	#77
EUVL diyAudio Member Join Date: Oct 2003	Too high for me even for the 1704. But I know some people has tried the 1704 with 22R passive IV followed by tube stage. So maybe 3x 844 in parallel will do .... I still prefer my SEN, by far. But then I am biased. Patrick __________________ xen-audio.com

15th January 2013, 06:30 AM	#78
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	Input Z for the AD844 is 50ohm typical, , and happy with it is an understatment, it's a game changer as far as being compared to the normal highend opamps with feedback. This AD844 when used without global feedback and even with it's own output buffer has made me feel that all other opamp based I/V's are seriously flawed, and I don't think I have it at it's best yet either. Someone said it needs to be biased higher than it's quiescent current of 6.5mA, but correct me if I'm wrong but the PCM1704 can only give +-1.2mA at full swing 0dbf. But maybe they meant with the TDA1541 which gives out a much higher than that. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com


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15th January 2013, 01:33 AM	#71
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	dont have time now, havent read them for years. i'll look into that when I refresh on his articles soon, looking to do a layout of the recent shunt version. but another point I will make is that Walt is not the only one to have had trouble with AD797 at low or unity gain. its one of the reasons its been labelled as a somewhat cranky opamp. maybe its simply that running at low or unity gain accentuates issues with problem PCB layouts that would otherwise be fixed with higher gain.

15th January 2013, 03:27 AM	#76
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	yeah its too high for ESS or I would try it

15th January 2013, 08:51 AM	#79
EUVL diyAudio Member Join Date: Oct 2003	We have eventually built the AD844 discrete using BC550 / BC560 (see the link above) ourselves to get to the low Zin of <10R. I still prefer the SEN in an A-B test. Patrick __________________ xen-audio.com

15th January 2013, 11:54 AM	#80
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	What about this IV for PCM1704?

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