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Old 14th November 2012, 01:12 AM   #21
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Originally Posted by qusp View Post
I don't think your noise performance will be lower than LME49990, which requires none of that (except the bypassing)
Yah, for a 1k feedback resistor it's about 100nV RMS in favor to the the AD797, assuming typ parts and a 20k bandwidth. That's approximately do not breathe on measurement setup levels and negligible compared to the ground bounce developed across unbalanced interconnects---even with balanced interconnects and 0.1% resistors it's likely smaller than the ground bounce that gets through the receiver's 60dB CMRR. Glen, more on op amp noise models here or in any number of other references.

That said, I want some of these anyway, just because they're cool. RGs are rather more affordable, though.
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Old 14th November 2012, 11:07 AM   #22
qusp is offline qusp  Australia
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thats assuming a good PCB for the AD797, which is certainly not guaranteed here.

why bother with the vishay part when you can order the exact value you need from the company that developed the technology Texas components even if its a single 835.45 ohms chip its still slightly cheaper to order direct. I already use the ASMP in my headphone amps and IV, have so for years, excellent resistors. the Texas parts are cooler too, they have a clear conformal coating, so they are 'naked' like their bretheren.
Attached Images
File Type: jpg ASMP Zfoil SMD 3 web lorez.jpg (122.8 KB, 43 views)
File Type: jpg Zfoil SMD ASMP identical lorez.jpg (135.9 KB, 42 views)
File Type: jpg TSMP naked smd Z foils on IV closeup.jpg (323.2 KB, 44 views)
File Type: jpg TSMP naked smd Z foils on IV relcap.jpg (255.4 KB, 42 views)

Last edited by qusp; 14th November 2012 at 11:11 AM.
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Old 15th November 2012, 01:44 AM   #23
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Sure, but the point was the 49990's current noise is negligibly higher than the 797 even in the ideal case where the 49990 might arguably be lower performance.

Interesting about Texas Components. I've yet to hit a problem I couldn't solve satisfactorily with standard values and it their website doesn't seem to offer online ordering; is this a must call/email/fax a special order kind of arrangement?
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Old 15th November 2012, 04:06 AM   #24
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oh I know, wasnt arguing with what you said I agree, but I think swapping into a design not made for it the lme would have the advantage.

yep email only, they make to order with most orders, but do hold some standard values in stock I think. still very slightly cheaper even if you dont need the custom value, they even make resistor networks using the same tech, you can order in global + relative value match in pairs, quads etc. I mostly just stick to global, but for the above I got the sets as relative pairs too
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Old 15th November 2012, 06:07 PM   #25
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Originally Posted by qusp View Post
thats close enough to just call unity.... so I did... really without careful layout and without some additions, I wouldnt use it lower than 4x. AD797 not properly implemented will be handily beaten by lme49990, which is a fairly bulletproof chip too, cheap as well.
AD797 even has completely different pins that need to be used to gain best performance from it (pin 8) that are probably just tied to ground or unconnected on your layout. once you combine figure 39. figure 42. and figure 44 (along with the recommended psu bypassing) without a suitable PCB..... I dont think your noise performance will be lower than lme49990, which requires none of that (except the bypassing)

great chip, but its a princess (sorry Scott =) you know its true)
thanks again for jumping in on this

I will use compensation from pin 8 as everyone who uses this chip says it`s mandatory

right now it is without comp on brown dogs and either the crappy smd components are making it sound bright or it`s oscillating and I won`t know till I get an oscilloscope because it`s not overheating but it`s like someone throwing glass in my eyes lol

what should I look for in used o scope?

downloaded pdf for lme49990 and looks to be similar speed and may change to something different for op but for now I will try 797 but in between jobs right now so all on hold

thanks for the strait answers
Glen
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Old 15th November 2012, 06:27 PM   #26
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Originally Posted by twest820 View Post
Yah, for a 1k feedback resistor it's about 100nV RMS in favor to the the AD797, assuming typ parts and a 20k bandwidth. That's approximately do not breathe on measurement setup levels and negligible compared to the ground bounce developed across unbalanced interconnects---even with balanced interconnects and 0.1% resistors it's likely smaller than the ground bounce that gets through the receiver's 60dB CMRR. Glen, more on op amp noise models here or in any number of other references.

That said, I want some of these anyway, just because they're cool. RGs are rather more affordable, though.
I as of yet do not understand common mode rejection?

I assume ground bounce is noise from ground or virtual ground?

thanks for the links and I have heard stellar opinions on vishay bulk foil and less so on sumono and yes I will fork over the ridiculous price for the final outcome because I have heard they are liquid audio whatever that means?

It sounds yummy lol
Glen
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Old 15th November 2012, 06:31 PM   #27
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nice job Qusp

do you think the difference between naked and not can be heard?

and no I don`t need test results lol

Glen
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Old 15th November 2012, 08:43 PM   #28
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Originally Posted by GLENZWORLD View Post
what should I look for in used o scope?
Tek 2215 is a good starting point.

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Originally Posted by GLENZWORLD View Post
I as of yet do not understand common mode rejection?
See references linked previously.

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Originally Posted by GLENZWORLD View Post
I assume ground bounce is noise from ground or virtual ground?
That's part of it, though non-noise currents can easily dominate---ground traces/wires/planes/whatever have nonzero impedance so the potential varies across them. For example, a power amp usually pulls more current than a DAC or preamp so its ground voltage changes more with the charging pulses through its bridge. Since an unbalanced interconnect has 0dB CMRR all of the difference between the DAC/preamp and power amp's ground potential is seen as signal at the power amp input. Multiply by a typical power amp gain of 25-30dB and one begins to have a case for why things like power cords can be audible.

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Originally Posted by GLENZWORLD View Post
I will fork over the ridiculous price for the final outcome because I have heard they are liquid audio whatever that means?
Generally speaking if your design has a hard requirement for better than 0.5% Susumu RRs or similar it's probably not the right design---think twice before spending more than 10 or 11 cents on a resistor. That said, 0.1% RGs are under 50 cents in small quantities so they can be attractive if one's in a mood to splurge a little.

I might be forgetting something but I think the most expensive resistors I've ever bought are Vishay RH050s for power amp testing---for DACs if you need more than a 1/10W 0603 there's a decent chance you're doing something wrong. That doesn't mean the possibility of buying matched quads isn't pretty cool but, let's be realistic, in most applications it's like buying a $100 bottle of wine rather than a $10 bottle---you do it because you want to, not because you need to.

Quote:
Originally Posted by qusp View Post
oh I know, wasnt arguing with what you said I agree, but I think swapping into a design not made for it the lme would have the advantage
Oh, sure I agree. Though either of these op amps is arguably overkill; the 49990 or 797 doesn't move THD+N much to the left of a 49710, 49722, 49724, or 49740.
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Old 15th November 2012, 08:53 PM   #29
qusp is offline qusp  Australia
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THD yes, but apart from in regulators ive not really been much of a fan of those, maybe its snobbery =) but there are other factors, the input offset of the 49710 isnt so hot from memory either.

they are actually cheaper than I remember for the ASMP. I checked back last night, I was thinking of the matched sets price or a higher resistance I think, just normal global match ASMP1206 zfoils for the low range values (they get more expensive as the resistance gets higher, longer laser etching/cnc path I guess) like less than 1kohm its $7.84ea for 0.1% more for the matched quads but thats just to satisfy neurosis

I like RG too, they are my second choice, well vishay MELF arent too bad, but at some suppliers you dont pay that much less than the foils

liquid? lol sorry I dont really do that sort of language, the naked resistors are not really naked, they have a clear conformal coat, its the foil element that makes the difference, not being 'nude'

really excellent for TC, any application that might show some self-heating from voltage or whatever, for that the zfoils blow everything else away, rock solid, check the video out where he points a hot air tool at them after freezing them, doesnt budge

Last edited by qusp; 15th November 2012 at 09:18 PM.
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Old 15th November 2012, 10:19 PM   #30
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Originally Posted by qusp View Post
the input offset of the 49710 isnt so hot from memory either
It's 50uV typ, same as the 797 and less than the 49990. I would be curious as to the audio application where 50uV is significant and what op amp would be a better choice (other than the 49722 at 20uV typ).
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