And the Audio-Gd Reference 10 has a MUCH THICKER front panel.... and I am a sucker for thick front panels!
Seriously, there is an assumption in high-end circles that high current, linear DC supplies give better sound than switching supplies; I think the "reasons given" are twofold:
- Switching supplies may contaminate other circuits with their RF noise, either through their DC output or through capacitive or inductive coupling.
- Linear regulators offer lower impedance outputs, especially at higher frequencies, which provides better sourcing AND SINKING of currents which D/A converters and analog stages draw.
If you look at designs like the Conrad-Johnson preamps, they understand that power supplies are more than just a block on a diagram from which current is drawn when needed; the power supply forms an integral part of the audio circuit, supplying as well as sinking currents originating in the active devices of the preamp. Therefore, C-J has turned to using all film and even teflon type capacitors in their preamp power supplies to squeeze that 'last margin of audio goodness' out of the signal. (That's right, some C-J preamps have NO electrolytics in the B+ supply, only great big film caps.) Audio-Gd follows a similar idea with their overkill class-A regulators- they are taking steps to keep power supply related factors from hindering audio performance. The power supply doesn't have as much impact on the sound as the parts directly 'in series' with the audio signal, but they DO have an impact, so once all the "direct audio signal" designs are as linear as possible (DAC and analog stages) the next area to improve is the power supplies- to bring the sound "that much closer" to sonic nirvana. We all know that the last 5~10% of sonic improvement often accounts for 75% of the cost.
R-Core transformers, used in the more costly Audio-Gd products, do usually measure lower in line noise transmitted through them than other types of transformers. (R-core transformers have lower primary-to-secondary capacitance than other designs, hence less high frequency hash is coupled into the power supply from the line.) I don't think switching supplies are particularly good at suppressing RF and other noise coming in on the power line, especially common mode noise. They DO filter it out to a degree, but I think that R-core transformers followed by linear supplies would do a better job.
Also, Audio-Gd doesn't use IC op-amps in their analog stages. Here, the thinking is:
- You can hand-select and hand-match parts in a discrete gain stage, not possible in an integrated circuit
- IC op-amps rely on negative feedback, sometimes quite heavily, and there is an opinion (some would say a "fashion") that negative feedback can hamper the dynamic operation of audio circuits. Rather than use a 'good' circuit made to measure "great' by use of negative feedback, the trend is to make circuits that are very linear, wideband and have low output impedance to begin with, and eschew negative feedback as much as possible. Often this requires hand-selecting semiconductors. Audio-Gd doesn't use negative feedback in some instances where it's been common practice to use it.
Using ACSS, and placing the volume control in the ACSS circuit, should have an advantage. I think this is because solid state circuits offer better linearity in current gain than in voltage gain, though my understanding of this is incomplete- I really don't know the topology of the ACSS designs and I am shooting from the hip when I try to understand the advantages of current-domain designs like ACSS. I know using ACSS (or CAST as used by Krell) offers advantages in signal transmission over cables- cables between a CAST output DAC and a CAST input preamp should have nearly zero impact on sonics - but we have no ACSS (or CAST) cables in the Reference 10, just internal signal wiring. The Reference 10 does have ACSS outputs for use with Audio-Gd power amps and preamps, but the advantages of ACSS when used in a stand-alone DAC must lie elsewhere than in terms of signal transmission. I know Mark Levinson also used volume controls in current-gain stages in some of their well-regarded preamps. I would welcome more explanation and discussion of ACSS and the similar CAST concepts from any engineers out there who are familiar with these things!
Does all this engineering and philosophy result in better sound? ONLY LISTENING COMPARISONS CAN ANSWER THAT QUESTION!!!! I would love to be able to do some blind A/B comparisons of these high-end DACs. Unfortunately, although I might buy an Audio-Gd Reference 10 sometime soon - I do not have other similarly-priced DACs, like the Fostex or Jade to compare.
OK, so I don't KNOW if the "Audio-Gd Way" results in better sound, but I am going to bet it doesn't result in WORSE sound, and I LIKE the implementation in the Audio-Gd products. This is a question of engineering aesthetics, not of sonics. Yeah I DO listen to this gear, but aside from listening pleasure, I get satisfaction from the 'objectness' and the design philosophy implementation because I am a technical guy and just like technical things. I really get a rush from opening an Audio-Gd product and looking at what's going on in there. This is maybe 40% of the enjoyment of the gear for me. It's like looking at a painting, in a way. It's a kind of art.
Edited by milosz - 4/25/12 at 2:35am