DAC AD1862: Almost THT, I2S input, NOS, R-2R

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miro1360

Member
Joined 2010
@surfparadise
AD1862 is final ... everyone prefers a different style of power supply, a different style of I/V, it is not possible to fix people to any universal PCB, and the path of modularity is probably the best way so far and most diy friendly ... maybe I'll make a power supply PCB in the future :)

@laserscrape
he should use trafo with ratio 1:10 to avoid that resistor
 
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lasercut

Member
Joined 2017
If i understand correctly the trafo will reflect the load on the secondary to the primary, so without a resistor the output level will vary depending on input impedance of next stage after the trafo. With zero global feedback in next stage it could be reasonable to have no resistor with 1:10 step up, tube or high global feedback stage may be too high for the DAC output
 
diyiggy

diyiggy

Disabled Account
Joined 2019
laserscrape said:
The trafo also needs an I/V resistor, either in parallel with the primary or secondary of the trafo.
Not sure of the advantages of having it on primary or secondary, I think if the primary winding resistance is too high the IV resistor must be on the primary.
My trafo does not have centre tap on the secondary and it can still drive a balanced input, not sure if thats possible with all trafos though.


The trafo is an awfully expensive option and probably wont outperform either a passive IV resistor without a trafo or op amp IV, simply has its own set of compromises.
The trafo is probably the most ''natural'' sounding but the least transparent option to my ears.

Actually ''least transparent'' is not really accurate, least consistently transparent would be more correct, it depends a lot on the music how well it performs.
Click to expand...


Better to focus on a good R//C for that task...Rohpoint, Vishay Precision thick film power resistor or wired smd bulk resistor... lot of good option, as for the filtering capacitor if one is listening non oversampled.
 
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euro21

Member
Joined 2004
Paid Member
laserscrape said:
If i understand correctly the trafo will reflect the load on the secondary to the primary, so without a resistor the output level will vary depending on input impedance of next stage after the trafo. With zero global feedback in next stage it could be reasonable to have no resistor with 1:10 step up, tube or high global feedback stage may be too high for the DAC output
Click to expand...

For example I use 1:18.7 Sowter 8347 (now obsolete) as I/V after my PCM63 chips. Only secondary loaded with 2k2 resistor.
 
diyiggy

diyiggy

Disabled Account
Joined 2019
yep, I have that ones - in facts I tested dozen of resistors for my TDA1541A dac-

I today use the double wirewound Rohpoint for my main dac, but we know thick film with low ppm is the technology of choice for that I/V passive purpose.

I also thinked to these from VPG, particulary to the SN-4 non inductive- - look at datasheets options in the S & SL resistors- : pdfs.


Edit : I can not believe it : I got my pcbs today : less than a week from JPLCB ! Wow ! Have to Mouser but the passives parts, I have half a tons of fresh capacitors... cause I test not only reading the datasheets, lol - but who cares, you know caps is the poor side of knowledges for many ego sided IE, even a blind test may revel... and well we have not all the same hifi devices and I like to adapt cool designs like that one to the surroundinds devices !
 

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diyiggy

diyiggy

Disabled Account
Joined 2019
miro1360 said:
My favourite is LME49990, but it has been obsolete for a long time and according to TI it will not be produced anymore :D When I bought it from ebay and compared it with my genuine, the one from China was 100% fake or remarked. ADA4627 is very good, if not the best replacement for LME49990 in my opinion. Nothing wrong is with ADA4898-1 (I have a typo in BOM :D)
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Hi Miro i have a doubt at re reading the thread to write my bom for Mouser.


Is the inputt above is just for a buffer in the scenario of an other oap for the I/V purpose or was it wrote in the particular case of swapping the opa627 from your pcb as first choice in the purpose to be both I/V and headphone buffer ?
 
diyiggy

diyiggy

Disabled Account
Joined 2019
so oaps both active i/v & buffer purpose ? I didnt see if there was a passive I/V stage made from a shunted resistor before and eventually mix with a previous conversation about passive I/V circuitry with you ?


So Buf634 not advised here but in a further verroboard as extra buffer I asurmise ?!
 
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