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In Reply to: RE: Digital volume control versa passive pre-amp posted by SashaV on April 19, 2008 at 16:49:28
"I am a bit confused, you mentioned passive analog gain control, how can I gain anything if it is passive?
Or is this just a term for passive pre-amp?"
You can call it a "passive pre-amp," if you like. I don't like to use that term, because it is an inaccurate neo-logism. There is no amplification with a passive device. You can still control the gain with a passive device, so long as you are content with reducing the gain.
There are a lot of combinations to compare, e.g. 16 bit program material vs. 24 bit program material, Wadia vs. DAC, digital vs. analog volume control, passive vs active pre-amp, etc. (This works out to sixteen combinations that I have listed and there are more tests possible.)
Let's assume that you are using a regular preamp and are playing the Wadia into it, and let's say you adjust the volume by a combination of the Wadia digital volume control and the preamp volume control to a comfortable but loud listening volume. You will want to maintain this same level for all of your tests. I suggest two tests of this configuration: the first with the Wadia digital volume control all the way up and the preamp volume adjusted to taste, and the second with the Wadia turned down 15 db and the preamp volume turned up to match the original level. Do you get the same sound? If so, then the digital volume control is doing its job well.
Repeat the same tests using your DAC. Compare the DAC with full scale digital volume control (or no digital volume control) and with 15 db of digital attenuation. Again, if the two sound the same then the digital volume control is doing its job well. If not, something is wrong, e.g. the software performing the digital volume control is poorly written, the O/S or drivers are interfering with the DAC resolution, or the DAC itself has significantly less than 24 bit resolution, probably less than 20 bit resolution.
Assuming you have enough gain in your amp, which is likely with either the Wadia or your DAC, you can repeat these experiments using a passive preamp. However, be advised that a passive preamp will not reverse polarity and an active preamp probably will. With some music, some speakers and some listeners reversing polarity may make a difference, and depending on particular circumstances may make the sound better or worse. If you want to conduct accurate comparisons you will need to control for this. You can control the system polarity by reversing both speaker leads. You will likely find that that a passive preamp sounds better than an active preamp. However, depending on the particular equipment, length of your interconnects, etc., this may not prove to be the case.
If you are like me, you will want to repeat the tests with your highest quality program material, which probably means high resolution material. I have found that going from 16 bits to 24 bits generally makes a larger improvement than going from 44,100 Hz to 96,000 Hz, but I longer hear to 21,000 Hz, as I could when young. YMMV.
Tony Lauck
"Perception, inference and authority are the valid sources of knowledge" - P.R. Sarkar
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