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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




celander
celander's avatar
celander OP
1,036 posts
 
@georgehifi I looked at the owners manual after posting. I think you are correct about the digital domain volume control. Here is what their manual says:

“HGC is Benchmark's unique Hybrid Gain Control system. The DAC3 combines active analog gain control, passive low-impedance attenuators, a 32-bit digital gain control, and a servo-driven volume control.

“All inputs are controlled by the rotary volume control. This volume control moves in response to commands from the remote control. Analog inputs are never converted to digital, and digital inputs never pass through an analog potentiometer. Digital inputs are precisely controlled in the 32-bit DSP system. The DSP system preserves precise L/R balance, and precise stereo imaging, while avoiding any source of noise and distortion.

“Benchmark's unique passive output attenuators provide distortion-free gain reduction without reducing the dynamic range of the converter. The attenuators optimize the gain staging between the DAC3 and the power amplifier. This optimization is absolutely essential for maximizing the dynamic range of the entire playback system.”

The output impedance isn’t uniform as a function of the different passive attenuator pads:
Attenuator:      Output Impedance
0 dB                      60 Ohm
-10 dB                 425 Ohm
-20 dB                 135 Ohm





georgehifi's avatar
georgehifi
4,966 posts
 
Hybrid Gain Control system
Yes that "hybrid" word says to me half digital, half analog. The the gain setting (0--10,-20db) is done in the analog and the volume is done by the ess in the digital.


The output impedance isn’t uniform as a function of the different passive attenuator pads:
Attenuator: Output Impedance
0 dB 60 Ohm
-10 dB 425 Ohm
-20 dB 135 Ohm

The output impedance isn't uniform as a product of the gain setting, not the volume control.
That’s because the gain is most probably changed via different feed back resistors of the output buffer which will effect it’s output impedance, not to worry though, they are all low enough for your active ATC speakers.
Just use good quality low capacitance interconnects to them say ( less than <100pF "picofarad" per foot) ask the manufacturer. Keep them short as possible 2-3mt will be fine

Cheers George
georgehifi's avatar
georgehifi
4,966 posts
 
BTW: Good on Benchmark for recognizing "bit stripping" even in the ESS-ES9028PRO converter and implementing an analog user changeable gain bock setting like Wadia and ML did. Bricasti did too in the M1 but you change theirs differently. 
https://ibb.co/d69hD9


Cheers George

 
celander's avatar
celander OP
1,036 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


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