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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
almarg's avatar
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almarg
8,673 posts
 
Your analysis is well done! And accurate to a very close approximation.

The DAC will see a load impedance of 9K + (1K in parallel with 100K), which is extremely close to 10K.

The amp will see a source impedance (the impedance seen "looking back" from its input) of 1K in parallel with (9K + 100 ohms), or about 0.9K, which in terms of impedance compatibility is slightly better than the 1K you assumed.

The one other consideration is that if the DAC utilizes a coupling capacitor at its output, which is particularly likely if its output stage is tube-based, its output impedance may be significantly greater at deep bass frequencies than the specified 100 ohms. But even if that were the case, the nominal ratio of 100x pretty much assures there won't be an issue.

Good luck. Regards,
-- Al
pbnaudio's avatar
pbnaudio
1,534 posts
 
GoldPoint 47 Step 10 kOhm Attenuator

Above link to a very nice attenuator, I believe you can buy them in a chassis with all the connectors etc as well.

Best of Luck

Peter
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
4,966 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."
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