
Home  Forums  Rules  Articles  diyAudio Store  Blogs  Gallery  Wiki  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Digital Line Level DACs, Digital Crossovers, Equalizers, etc. 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
12th January 2013, 01:57 PM  #31 
diyAudio Member
Join Date: May 2011
Location: Virginia

Yes, but notice that the very small value carbon resistor is used to minimize the lead inductance of a large tantalum capacitor, not the smaller 0.1uF bypass capacitor. This technique appears to only be useful when using relatively large bypass capacitors and only if you use a carbon resistor, or some other type that has very low inductance at radio frequencies.
__________________
photos of my work: https://www.facebook.com/SwetoneAudio my blog: https://plus.google.com/u/0/b/111642...44611308/signatures 
12th January 2013, 02:05 PM  #32 
diyAudio Member

If the inductance contributed by the resistor concerns you then select a smaller package size  0603 perhaps or 0402 if your eyesight is good enough. Its the total loop inductance that's important, not just that of the resistor  so if the resistor adds to the loop area it will increase the inductance. OTOH if the resistor's just replacing a wire that would be there anyway, it won't add inductance. This is assuming normal thick film SMT resistors of course, not wirewound ones.
__________________
'The total potential here must be nothing less than astronomical.' 'Nothing less. The number 10 raised almost literally to the power of infinity.' 
12th January 2013, 02:16 PM  #33  
diyAudio Member
Join Date: May 2011
Location: Virginia

Quote:
I assumed that the datasheet portion under discussion applied to through hole devices (since the AD797 is available that way) which have more lead inductance than SMD's. The datasheet specifies a carbon resistor.
__________________
photos of my work: https://www.facebook.com/SwetoneAudio my blog: https://plus.google.com/u/0/b/111642...44611308/signatures 

12th January 2013, 02:28 PM  #34  
diyAudio Member

Quote:
The use of snubbers is less important for decoupling purely analog circuits that aren't handling fast rise time signals and hence aren't taking big, fast gulps of current like CMOS digital chips do. I do recommend them for such applications, on pure analog handling audio band signals its a tossup whether there's any benefit.
__________________
'The total potential here must be nothing less than astronomical.' 'Nothing less. The number 10 raised almost literally to the power of infinity.' 

12th January 2013, 02:38 PM  #35  
diyAudio Member
Join Date: May 2011
Location: Virginia

Quote:
Obviously, digital circuits have different power supply requirements than analog ones, and it's debatable whether or not an opamp in an IV converter for a DAC sees enough digital surges to warrant this kind of snubber circuit. I would like to see some hard data on that before bothering with it. Do you have any?
__________________
photos of my work: https://www.facebook.com/SwetoneAudio my blog: https://plus.google.com/u/0/b/111642...44611308/signatures 

12th January 2013, 02:47 PM  #36  
diyAudio Member

Quote:
Quote:
__________________
'The total potential here must be nothing less than astronomical.' 'Nothing less. The number 10 raised almost literally to the power of infinity.' 

12th January 2013, 02:56 PM  #37 
diyAudio Member
Join Date: May 2011
Location: Virginia

I may be forced to use SMD's in the near future, so I have some interest in this idea. The LME49990 is particularly difficult to implement, according to their data sheet (and comments by others), for example, and this technique may be useful for that part. I'd be interested if you know of someone who has made this comparison if you don't have it. I assume that Analog Devices didn't invent this idea out of thin air but instead came up with it to address a specific problem they were having with the AD797. I understand the theory of course, but would like to see data on how much of a difference it makes. I can try to do a Google search myself but I am not hopeful about finding something useful.
__________________
photos of my work: https://www.facebook.com/SwetoneAudio my blog: https://plus.google.com/u/0/b/111642...44611308/signatures 
12th January 2013, 03:02 PM  #38 
diyAudio Member

Power supply decoupling would be the least of your worries if you're considering either of those opamps in close proximity to anything digital as I understand they don't coexist very happily with RF. Walt Jung (who works for ADI) even designed out the AD797 in his regulator as it misbehaved when powering digital stuff.
<edit> Here's a paper which anyone considering an opamp with input LTP for I/V would do well to read and digest : http://www.uemc.polito.it/papers/opampsusc_01.pdf
__________________
'The total potential here must be nothing less than astronomical.' 'Nothing less. The number 10 raised almost literally to the power of infinity.' 
12th January 2013, 04:02 PM  #39  
diyAudio Member
Join Date: May 2011
Location: Virginia

Quote:
No, I'm not considering either opamp for an IV converter for a DAC. The IV converter I have is based on the LME49710.
__________________
photos of my work: https://www.facebook.com/SwetoneAudio my blog: https://plus.google.com/u/0/b/111642...44611308/signatures 

12th January 2013, 04:08 PM  #40 
diyAudio Member

Out of that exNational range the only part I'd recommend for I/V duty would be the LME49713 because its CFB therefore no LTP to suffer the assault of all that RF.
__________________
'The total potential here must be nothing less than astronomical.' 'Nothing less. The number 10 raised almost literally to the power of infinity.' 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
AD844 as a common base stage in the I/V converter  Pedja  Digital Source  44  14th September 2015 10:10 AM 
WTB AD844 Opamps  apassgear  Swap Meet  6  31st January 2007 02:57 PM 
New To Site?  Need Help? 