Quote:
| What do you use for the I/V, rick? Do you use passive, and if so would you care to share what value resistor you found to work and what sort of filtering you have after it? AN seems to use a 380R, and most folks say to stay below 400R and I've seen as low as 100R. I've been working on my own "ripoff" for a while and am not sure what to use on the output. I'd like to stay passive, and for my first project, cheap (i.e., no transformers for now). |
I have tried a straight resistor as the IV,Resistor/Transformer IV,discrete transistor IV,discrete mosfet IV,and am one of these years going to try the transconductance amp (have the chips,not enough desire/time yet
) and so far this I find this IV/Output stage to sound best to my ears :
http://www.geocities.com/yury_g/dac1865.gif
http://www.sowter.co.uk/specs/8347.htm
Yuri's Retro DAC has only one real weakness and that is the CS8412/AD1865 interface so I used the one shown in the AudioNote DAC schematic.
Back to IV :
What I have learned and it took a while is it is not do much the method used as it is how much you ask the DAC IV output to do and from my listening tests anything over 220 ohms is off the list as making the DAC output sound as if it is clipping by being forced to do more than it is capable of.
So the trick is to get into the 100mv range of the resistor or resistor/transformer combo then add active gain to makeup the difference of what you have and what ytou ultimately need.This combination of active and passive seems to be the least comprimised in all areas and especially so in the bass region where the simple resistor loses some power even though it rules in the mid to upper octaves.
right now the AD1865 DAC is the best sounding DA Converter I own and that includes a stable of PCM1702,PCM1704,PCM61,AD1861 and a couple of "seriously flawed" PCMXXX USB DACs.A situation I hope to change soon by mating USB to the AD1865 through the I2S inputs if i ever get around to it.
Also.
Even though conventional wisdom says you
must have a multilayer pc board for a proper dac layout like Yuri i have mine on a perf board and it works just fine and the additional time it would take to layout a
proper board (which unless I planned additional copies not needed in my "one of" world) I instead spent listening and evaluating modifications to the output stage until I found a combination I liked the sound of in my system.The only thing i think I can do to better it would be full DC power from a battery/cap bank but if that happens way down the list of priorities
Hope this helps
