use D1 I/V with voltage output dac - diyAudio
 use D1 I/V with voltage output dac
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 11th June 2006, 02:36 AM #1 diyAudio Member   Join Date: Aug 2005 use D1 I/V with voltage output dac Go easy with me on this as I am relatively new to all of this. The question is how to use the D1 output stage with a pcm1751, voltage out dac. I know that a transistor is a current amp. I know that adding a resistor before the first transistor can convert v to I (and vice versa). The dac puts out 2.5v To calculate the resistor: V=IR, so R = V/I If we set the desired current to 2ma, then R= 2.5/.002 = 1250 ohms Does this seem salient? Is there anything else I should do, like couple with a cap as well? Thanks
 11th June 2006, 03:46 AM #2 diyAudio Member     Join Date: Jan 2002 Location: Tucson, AZ Blog Entries: 14 Why do you want to do this? The D1 is a I -> V stage, you already have a voltage out, why convert the voltage to a current and then back to a voltage again? What you need is a buffer and/or some filtering. Look into one of the Pass preamps if you are really set on a Pass design.
 11th June 2006, 05:16 AM #4 diyAudio Member     Join Date: Jan 2002 Location: Tucson, AZ Blog Entries: 14 Yes, the math is OK, have fun.
 11th June 2006, 09:23 AM #5 diyAudio Member     Join Date: Feb 2003 Location: Safe and sound Haven't seen it clearly from your post, but use the resistor in series between the Dac Output and the Mosfet Source. No need of a coupling cap. __________________ /Cheff - Falling feels like flying, until you hit the ground
 11th June 2006, 02:12 PM #6 diyAudio Member   Join Date: Aug 2005 Thanks.
 11th June 2006, 07:47 PM #7 diyAudio Member   Join Date: Aug 2005 I had 1.5k resistors on hand and it is working fine and sounds great. Question, though, the data sheet recommends using a 10uf polarized cap at the voltage output of the dac. I tried inserting the D1 circuit before the cap but it did not work (bad noises) unless after the cap. The data sheet does not describe the reason, only that it is needed and that the dac is ac coupled. Is this blocking DC? Any thoughts? Is there a reason that it would sound as good as it does with some budget cap in the signal path?

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