Originally Posted by borrego
You don't understand, do you?
Using the DAC volume control at any volume setting but max will decrease the S/N ratio from the point of the OPA1602, making it more susceptible to the "dirty" external PS. Using DAC built-in volume control is never a "Hi-Fi" circuit design. You can ask people at the Dedicated Source Components forum.
DAC built-in volume control is NOT equal to the implementation of using a dedicated digital volume control chip at later (pre-amp) section of the circuit.
Using external AMP, I can max out the DAC volume to maximize S/N, making it much less susceptible to "dirty" PS.
I suppose you do use shielded coaxle or twisted pair interconnect cables, don't you? Why don't you use straight bare wire interconnects, and say it is the dirty electromagnetic environment which causes the noise?
I understand completely...that you don't. You're the one using that unshielded cable by crapping up the supply and introducing noise. You called the noise current induced which was complete nonsense and shows your lack of understanding.
An amplifier is a controlled way to connect a power supply to a transducer. It's like a faucet for the energy. Screw up the power supply and you can't get a good result. If you want to know why the O2 amp was successful, that's it and it's ICs have much worse sig to noise ratios.
In this case, using the volume control in the DAC is better than using an outboard dig control upstream because the inboard one is extremely well engineered, bit perfect and avoids an additional a2d-d2a conversion processes of a later one upstream. Using a later analog control may be preferred but it's no slam dunk that there's benefit. In this case, it would be difficult to incorporate and in your scenario it would see large signal at it's input so low level tracking could be an issue.
The noise isn't coming from the DAC. The larger signal level of full on is masking the noise of the opamps when the PS is dirty or there is a ground loop etc. The noise is not a product of the DAC V control.
Edited by goodvibes - 5/7/14 at 5:02am