Optimizing Digital Volume Control

Steve, this is the theory. As I mentioned, nine out of ten of the guys on whatsbestforum with six figure systems end up adding a preamp to their DAC. They can't be all tone deaf and/or suckers. As Denon mentioned, you need to spend $20K (and up) to get the desired result, which they do.

Regarding preamp drive or DAC drive, the argument that the upstream component driving the amp should have a "low impedance with a lot of drive capability" while technically correct, in practice should be a non issue for any reasonable designed component. The input impedance of most power amps is 50K or higher (I know some are down to 10K), and with current state of electronics it is trivial to design an output stage with 200 ohm or less impedance. In fact if you look at reference preamps schematics they typically have a resistor in series at the output of roughly 200 ohm.I am guessing this is for protection against shorts. Regardless this tells me that reference level designers are not too concerned with having a very low output impedance. Otherwise removing that resistor would be the first thing an audiophile should do to get the best sound. I know that some of you may say that this has to do with impedance matching. Unfortunately physics tells us that for up to 20KHz bandwidth with short distances there is practically no impedance matching involved (unlike in the case of microwave or RF where the wavelength are on the order of the interconnect length or smaller). I believe the critical functionality for a preamp is minimizing noise and distortion that may be introduced due to attenuation or amplification, while presenting a high impedance to the source and reasonably low impedance to the load. I suspect that this is what differentiate a good (line stage) preamp from an average one.

Ed - 99.9% of iPod users use the stock earphones too. Means nothing. Means that they are just uninformed.

Steve N.
Empirical Audio

Oferi - The input impedance of an amp has nothing to do with the dynamic response to an input current and voltage signal. It's usually only a resistor to ground.

Just put a resistive passive linestage to an amp and you will typically experience a loss in dynamics.

Steve N.
Empirical Audio

Steve, bad analogy. iPod users use the stock earphones because they sound "good enough" and they don't feel the need to spend the money to get better sound.

Uber-audiophiles have exactly the opposite motivation; no preamp does NOT sound enough, and they are willing to spend the price of a mid size sedan to get better sound.

This is typically a highly informed decision, based on extensive auditioning of gear. I personally went through a few preamps that did not make the cut, a digital and analog volume control on a DAC and ended up settling for the arc ref5SE with transparent reference ICs and shunyata python zitron powercable (I threw in three stillpoint ultra's under the preamp for good measure as well).

I bought the preamp used with the intent of immediately reselling it if it did not improve SQ over the analog VC of my DAC (like I did with the Pass Labs XP-10 and the EMM Labs Switchman - resold within 48hours). If someone expertly "informed" me I was in fact getting worse sound because of some engineering principle, I would have still trusted my ears and kept the preamp.