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Old 8th January 2013, 05:51 AM   #11
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Originally Posted by KlipschKid View Post
I've listened to LM6171 - I used them with LM6172 in AMB's Mini3.
Rather like saying 'I've used a Ferrari, for a spot of shopping, it wasn't that bad'. That application is just an amp it seems to me, I/V duty is more like a racetrack in comparison to small town driving

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However, their performance is below that of the DAC IC so they won't do the DAC justice.
In terms of noise, I would agree. However that DAC's noise performance is way beyond what anyone can actually hear in a typical setup. In terms of distortion (in particular IMD) performance on complex tones (music for example) the normal amps do not do the DAC justice at all.
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Old 8th January 2013, 06:04 AM   #12
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.. I think of it more like putting ketchup on filet mignon ;-) But I have them so I can try...
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Old 8th January 2013, 06:06 AM   #13
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Oddly the term I use for the IMD (called by some 'detail') added by some of the parts you mentioned is MSG
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Old 8th January 2013, 06:21 AM   #14
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haha....... yummy... more mei jing... I tried LT1028 a while back - super bass ! No detail at all... "no salt and too much gravy"

It's a shame that many datasheets don't show internals - the ADA4627 sound as good as any I've tried in I/V stages, but I have no idea if they are ltp or cfp or ? input.
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Old 8th January 2013, 06:38 AM   #15
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The number rather gives this one away - its ADI's response to the OPA627. JFET but still LTP JFET. The OPA627 though still has one trump card to play over the ADA4627 - its dielectrically isolated. Why this makes a difference I don't yet know but it seems to matter
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Old 8th January 2013, 06:45 AM   #16
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I did wonder about the change in their naming style from 8 to 4....and ADI have been very keen to push the ADA4627 as "upgrade" to 797, 8610, etc, on their site. Anyway, the 627 sound good so for sure I'll try them.

Are any on my list cfp ? Do you know any fet that are cfp ? Or is there a good workaround you know ?
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Old 8th January 2013, 06:50 AM   #17
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No, none on your list are CFB - none of the ones I've so far mentioned are true CFB either since they'd not work in the current circuit without mods. A particular point is that a true CFB amp can't have a feedback capacitor or it goes wild

No, don't know any FET ones which are CFB but I agree that would be an interesting avenue to explore if anyone's up for designing a discrete stage, looks like it could be good...
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Old 8th January 2013, 06:59 AM   #18
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The CFB ones tend to have very high slew rates right ? Like 1500V/us instead of the 50V/us ?

I've done so much op amp rolling in the past for I/V and buffers, that I'd much rather give up on op amps and use a discrete stage. However, there's quite a range of designs for this too so it hardly makes it any easier to choose. Any tips ?
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Old 8th January 2013, 07:04 AM   #19
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Yes - right. As a general rule here the faster the slew rate the better the opamp is going to be at handling the overload conditions encountered in doing I/V.

As regards discrete I/V stages, I haven't yet exhausted all the possibilities offered by very wide bandwidth CFB amps. I'll only go discrete myself when I'm totally convinced no integrated solution will do the job adequately. I'm just lazy like that and a man's got to know his limitations. It would take me a seriously long time to learn analog design as well as the professional IC designers so I prefer to continue to scour datasheets for days on end looking for the right part Ask me again in a few months how its going...
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Old 8th January 2013, 07:13 AM   #20
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You deserve a medal if you manage that. How about something a little off-piste like a TPA6120 ? It's cfb...

The discrete I/V that interests me most is Rudolf Broertjes, except that it needs a coupling cap :

Click the image to open in full size.

from diyparadise.com
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