Uprgrading my Metrum Octave DAC

The Octave DAC is hard to beat, but the source is actually more important. There are two things to consider:

1) drive the Octave with a lower jitter source like Off-Ramp 5, Diverter HR or Synergistic

2) sell it and use a Wired 4 Sound DAC2 driven with I2S from an Off-Ramp 5 - this is a world class sound

Other than that, consider more expensive DACs that enable you to eliminate your preamp. The steps to good digital sound are:

1) reduce source jitter
2) eliminate or reduce the effects of digital filtering in the DAC
3) eliminate active preamp and drive the amps directly
4) couple to the amps directly using a good transformer and balanced cables

Steve N.
Empirical Audio

"An preamp is a preamp whether it's in the DAC or external. If you plan to control the volume, you are going to need one. The Octave does not even have a buffer and takes the output directly from the DAC chips. I choose to let a SP17 do the rest, partly because I love the ARC sound and partly because it's also a phono preamp and offers various input switching, remote volume, etc."

This statement use to be true, however there are new digital-only volume control technologies that allow the DAC line-out to feed the Amps directly, and I'm not talking about iTunes volume controlling 100% of the volume here. I'm taking about completely eliminating the preamp.

"Not interested in transformers, or capacitors anywhere they can be eliminated, especially directly in the signal path."

I understand your reticence, however there are also new transformer technologies available that improve sound quality dramatically. I use simple a buffer transformer after my DAC. Makes a world of difference. Here is why:

http://www.audiocircle.com/index.php?topic=108715.0

Steve N.
Empirical Audio

"Which DACs do you know of that are capable of doing this? I guess you just need a DAC with the right output impedance, why do you need balanced cables though?"

Any DAC with low output impedance can be used, lower than 50 ohms is good. If you drive the music from a computer, then the software player can control the volume. The problem with using most DACs line-out and controlling volume using software is the danger of having max volume and blowing up speakers. As for audio quality, as long as you use a max of -10dB and no more, the sound quality will not be impacted. This means using DACs with variable gain. The danger of speaker damage is still there. Therefore, I dont recommend this technique.

One DAC that you can drive line-out and actually control volume on is the Overdrive SE. This uses a digital volume technology that does not change the data. It changes the reference voltage of the D/A. The advantage of this is that it adds no actual parts to the signal path and changes nothing in the gain stage when the volume is adjusted. The THD actually decreases as the volume is lowered, unlike any other volume technology. This volume controls all digital inputs, so it can be used with computer or Transport.

Steve N.
Empirical Audio

"Every differential amplifier stage is true-balanced by default on both the input and output of the topology."

In your dreams. Most good balanced output stages are either tube or discrete, so there are several issues that make them imperfect:

1) DC offset
2) common-mode noise
3) difference in amplitude between + and - signals (impossible to make these identical with active circuits)
4) isolation of ground between DAC and amps

A good transformer solves all of these and makes the amps sound better in the process.

"Lastly, digital volume attenuation is hardly "new." Yes, there are methods of accomplishing this with technically no distortion. To me it's all unnecessary and yet another way to have your bitstream modified via DSP and I have no interest in that."

You are not getting it. This is not DSP. This is not software. This is not even a digital chip somewhere in the signal path. This is something entirely different. This is control of the D/A reference voltage. No modification to the digital stream. Nothing else like it.

Steve N.
Empirical Audio

Mabonn - I can only speculate why they sound inferior to .wav.

I suppose it must be due to the real-time behavior of the CODEC software in the computer. Statically, the data is not changed, but somehow when these compressed formats are played dynamically, it changes things. I have heard it over and over in different systems.

We can debate this until the cows come home, but that is the experience I have had. Also, all of the partners I have had at RMAF shows had the same experience.

Steve N.
Empirical Audio

Matt - you can convert all of your FLAC files to .wav using dbpoweramp on PC or XLD on Mac.

Steve N.
Empirical Audio