2. digital
  3. 137533-45726

DAC-Preamp having these specifications?

Rather than asking for feedback about specific products, I thought I instead would ask for your recommendations of a DAC-Preamp product(s) having a desired set of following specifications:

Output Impedance: < 300 Ohms
Balanced outputs (XLR)
Unbalanced outputs (RCA)
2 or more analog inputs (RCA or XLR)
2 or more digital inputs (coaxial + optical or USB)
DAC section preferably uses discrete components over op-amps
DAC signal processing capabilities should the usual fare though need not include every conceivable format
Price: ~$2,500 or less




128x128celander
celander's avatar
celander OP
1,502 posts
 
The owners manual of the all digital input version, DAC3 DX, makes even more clear the digital volume control of the outputs:

”The MAIN bus drives the XLR outputs and one pair of RCA outputs. The MAIN bus delivers the highest performance because it uses three conversion channels wired in parallel for each XLR connector. The main bus uses 6 of the 8 channels in the ES9028PRO D/A conversion chip. The remaining two channels in the ES9028PRO drive the AUX bus.“
audioengr
3,282 posts
 

There are essentially 4 ways to get volume control:

1) analog volume control that changes the gain of an active stage - can be controlled digitally

Disadvantage - change in gain characteristics at different volume levels and signal levels can affect dynamics or cause varying compression.  The lower the volume, the higher the distortion.  It usually adds a stage to the signal path as well, adding to the compression and distortion.

2) attenuation with resistors or optical controlled resistors

Disadvantage - large resistances in the signal path add thermal noise and can affect impedance and frequency linearity if used on outputs.  If this attenuation is between stages, the lower the volume, the higher the distortion, the lower the S/N ratio.

3) modify the digital words using DSP

Disadvantage - DSP usually impacts SQ if more than about -9dB of attenuation is required, even with the best DSP software, such as Sonic Studio.  For less than -9dB of attenuation, it works pretty well.  The difference between the quietest tracks and the loudest tracks can easily be 12dB.

4) change the reference voltage that the D/A conversion uses.

Disadvantage - it is difficult to turn the volume down to zero.  It can be quite low, but never zero.  Overall, the best solution of the 4.  Extremely low distortion and it gets lower as the volume is decreased, not higher like the other techniques.  No added resistance or stages to the signal path.


Steve N.

Empirical Audio


celander's avatar
celander OP
1,502 posts
 
@audioengr So the DAC3 uses method 2, with the attenuation arising after the last active stage? I’m unclear about this. 
audioengr
3,282 posts
 

No different than an external passive resistive attenuator. Changes impedance and can cause roll-off. Adds thermal noise. Critical to use low-capacitance interconnects with this type.  I stay away from these myself.

Another type of volume control I failed to mention is by transformer with multiple taps. An autotransformer is usually the design. This is typically not done in a DAC. Never seen it in a DAC. Quite expensive if done right with quality transformers, but this method has very few drawbacks. Only saturation of the transformers is an issue. Mostly the disadvantage is cost.

Steve N.

Empirical Audio

georgehifi's avatar
georgehifi
10,312 posts
 
So the DAC3 uses method 2
This (linked) is where I believe the volume is controlled in the digital domain before d/a conversion. The other so called "hybrid" part is just an analogue gain adjusting (0db -10db -20db) on the output buffer for the maximum level volts obtainable if the digital volume in the ESS chip is full up.

https://ibb.co/h4MbD9

Cheers George
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