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Passive attenuator impedance question

Hi,

I would like to build passive attenuators between my DAC and Amp (to reduce potential degradation in the DAC's digital volume control).

The DAC's output impedance is 100 Ohms and the Amp's input impedance is 100K. Using a 9K/1K resistor network I can achieve the desired 20dB attenuation. If my understanding is right, this attenuator will present itself as a 10K load to the DAC and an output impedance of 1K to the Amp. Both DAC-->Attenuator and Attenuator-->Amp will have a nice 100x impedance ratio. I read in another thread that > 10x is preferable.

Do you think these resistor values (9K/1K) are good, or should I go lower or higher? Obviously I am looking for optimal sonics. I realize the exact values will be system dependent; I'm just looking for some direction.

Thanks,
gmudunuri
zd542
5,339 posts
 
I don't think you'll benefit in any way by using a passive volume control. I know that when you lower the volume on your dac, you loose some resolution. I've done quite a bit of testing, along with a few other audiophiles that were curious, as well. Using a very detailed system, we couldn't hear any difference whatsoever between low and high settings. I think you're far more likely to lower SQ than raise it. To be fair, we only used Wadia products for our testing. However, I wouldn't expect different results if we tried other brands.
georgehifi's avatar
georgehifi
10,312 posts
 

If this is happening Zd542 the dacs volume control is "bit stripping" in the digital domain, this will not happen with a passive volume control in the analog domain.

Cheers George
zd542
5,339 posts
 
"07-06-15: Georgelofi

If this is happening Zd542 the dacs volume control is "bit stripping" in the digital domain, this will not happen with a passive volume control in the analog domain."

I know.

"I know that when you lower the volume on your dac, you loose some resolution. I've done quite a bit of testing, along with a few other audiophiles that were curious, as well. Using a very detailed system, we couldn't hear any difference whatsoever between low and high settings. I think you're far more likely to lower SQ than raise it."
almarg's avatar
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almarg
9,670 posts
 
Regarding "bit stripping," I would not extrapolate experience with Wadia models to models from other manufacturers, and perhaps even between different Wadia models.

The manual for the Wadia 121 states as follows:
Does the Wadia Volume Control compromise resolution?

The Wadia 121 Decoding Computer uses the latest generation of Wadia’s proprietary digital volume control. The volume level can be varied in the digital domain by means of mathematical manipulation of the signal, eliminating the distortion and noise that are inevitable with even the best analog volume controls. While conventional thinking indicates that reducing the volume digitally can sacrifice low level resolution, Wadia has created an innovative solution. Wadia’s patented digital filtering algorithm produces a 32-bit output. This high-resolution signal is then used in the computations that in turn reduce the volume level. This new signal is fed directly to the DAC chips. Through this innovative method, the Wadia 121 Decoding Computer maintains high resolution even at the lowest volume control settings.
While the manual for the 321 has no such statement but says:
A Volume Setting of 88% on the Wadia 321 will provide optimum performance when it is connected to a Preamplifier (Integrated Amplifier or Receiver).
Best regards,
-- Al
rodman99999
6,206 posts
 
Mr G- Something that may be of interest to you: (http://www.partsconnexion.com/controls_attenuator_khozmo_series.html)
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