Here is what works great for my PCM1704, if your doing a sub for another I/V opamp, don't forget to disconnect the feedback loop around the old opamp.
And give thanks to Pedja Rogic for letting this out of the bag, as I think it would be hard pressed for even a discrete I/V to better the sound this can give. And kudos Barrie Gilbert for designing the AD844 and abraxilito for the dac dc offset nulling circuit
Cheers George
And give thanks to Pedja Rogic for letting this out of the bag, as I think it would be hard pressed for even a discrete I/V to better the sound this can give. And kudos Barrie Gilbert for designing the AD844 and abraxilito for the dac dc offset nulling circuit
Cheers George
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> the 844 as-is is much better than almost all discrete circuitry
Except when you want to use it as a BJT CEN and wants lower input impedance than 65 ohm ?
(PS I like the 844 as well, especially as in LC's phono.)
Patrick
Some people are better with discrete than others
jan
ironic much? yes it was that series of articles I remembered it from, related to the superregulators.
in no way am I criticising Walt, or Scott's work, clearly they both know what they are doing..... I have had excellent results with the AD797, even at unity gain in Flea type regs, its one of my favorite opamps, perhaps THE favorite opamp.
It does require a bit of babying at low gain though in my experience and I believe its unity gain stability stamp should come with a disclaimer, because it is used in ways it is not really suitable for, by opamp rollers and designers alike because of this.
Jan, you mean pin 8?, yes the layout and component choice regarding this pin's use are critical, as well as being quite important to squeezing the most out of it. either use it properly or not at all IMO
that, is ironic.
perhaps your taste for it is not as refined as you think?
of course it was stability of the whole loop, isnt it always? but it was stability of the AD797 in that whole loop, so it was discarded and not recommended, replaced by AD825 if I remember correctly.
he could most likely have worked with it and fixed it in situ, but he was writing an article for others to implement and clearly there were a few issues that made it hard to recommend under this use case.
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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.
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.
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.
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.
Looks like George is happy with Zin = 65 ohm for his 1704 after all.
But I have the SEN, and the AD844.
http://www.diyaudio.com/forums/digi...-minimalistic-iv-converter-5.html#post2718757
Patrick
But I have the SEN, and the AD844.
http://www.diyaudio.com/forums/digi...-minimalistic-iv-converter-5.html#post2718757
Patrick
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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
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
