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Ideal I/V resistor ?
Ideal I/V resistor ?
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Old 4th November 2017, 10:22 PM   #1
Henderson is offline Henderson
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Default Ideal I/V resistor ?

Hello,


Please: what are the items needed for a good resistor for an I/V dac chip stage ?


read many things, can't decide : Rhopoint ? Caddock ? Vishay, Allan Bradley, Sussumu smd ?


Thick film ? Naked la Vishay or Caddock ? film type ? SMD ? carbon comp ? wirewound ? exotic ? high wattage ? Radial, axial ? Big, short ? vibration proof ? metal leads type and thickness ? Different choice according Z : 15 ohms type needs to be different than 2000 ohms for a good passive I/V


How to sort out ? Just a basic metal film ? But which ?


help & experience much appreciated
 
Old 4th November 2017, 10:52 PM   #2
miro1360 is offline miro1360  Europe
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why passive I/V?
 
Old 4th November 2017, 10:57 PM   #3
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Not correct word maybe ?


resistor shunted to ground between any dac chip current outputt or active parts after to convert current to voltage...


for instance for the 1 mA of an AD1862, etc...
 
Old 4th November 2017, 11:01 PM   #4
miro1360 is offline miro1360  Europe
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just a question why active I/V is not better option?
 
Old 4th November 2017, 11:16 PM   #5
Henderson is offline Henderson
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I questionned first
 
Old 4th November 2017, 11:24 PM   #6
jcx is offline jcx  United States
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Bruce Hofer of Audio Precision recommends 5pm TC or less thin film R for least distortion, better than bulk foil
 
Old 4th November 2017, 11:34 PM   #7
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Thank you very much jcx,


what is TC meaning please ?


Did he like a model/brand better than an other in his work ?
 
Old 4th November 2017, 11:35 PM   #8
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Henderson View Post
help & experience much appreciated
Like miro is suggesting - going active I/V (but not with opamps) is better than passive I/V as it gives the DAC the best possible circuit conditions to achieve its best SQ. I use a common-base transistor, sometimes I cascode it.
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Old 4th November 2017, 11:56 PM   #9
Henderson is offline Henderson
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me too : JFet CCS feeded; opa861 or discrete diamonds buffer... no feedback ! My fault, should not have said "passive" as I suggested as well.


discrete serie Darlington serie with zener or very low noise ref (btw which ones today ?) for regs...


Here i'm focussed on the I/V resistor... as it's a part thread... read many things but lost in all the resistor choices (read things from Walker member,etc, asf...)


Any experience about that passive part Abrax ? Anyway, if a shematic I take it too, don't like the idea of an 627 with feedback for I/V than Miro chose on his AD1862 headphone dac but think it will be surely off topic in this forum area...

Last edited by Henderson; 4th November 2017 at 11:59 PM.
 
Old 5th November 2017, 12:00 AM   #10
abraxalito is offline abraxalito  United Kingdom
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So far I haven't found the quality of the I/V resistor to be a significant influence on the SQ (I'm still using ultra-cheap thick film, have tried Susumu thin film). By this I don't mean to say it makes no difference, rather I mean in my experience it hasn't been the low-hanging fruit. There have been other, much bigger fish to fry - most recently that has been passive filtration of the DAC output prior to I/V.

btw 'TC' means temperature coefficient.
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