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Passive Preamp from DAC = volume control?

post #1 of 5
6/29/09 at 11:40pm
Thread Starter 
My monitor speakers with a built in amp are on stands far away from my desk. I was wondering if I could put the Axiom Passive Preamp such that MBP optical out => MoodLab Concept DAC => Axiom => Audioengine A5 amp.

I will try to use the shortest cables between the Moodlab Concept and Preamp, but there will be a rather lengthy (6 feet) cable after the Preamp to the Speakers. Will the preamp serve it's purpose as a volume control? Will there be distortion introduced?

From my understanding, there need to be enough power coming into the Passive Preamp and I'm not so sure if the MoodLab Concept is up to the task...
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post #2 of 5
6/30/09 at 12:44am
You should be fine -- cable length will not matter here, and in theory there will be distortion added but it will not be audible. I have the MoodLab Concept, a home-built volume control, and Audioengine A2's ... no problem. I feed them with optical out from a vintage Sony discman.
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post #3 of 5
6/30/09 at 4:13am
Thread Starter 
Quote:
Originally Posted by wavoman View Post
You should be fine -- cable length will not matter here, and in theory there will be distortion added but it will not be audible. I have the MoodLab Concept, a home-built volume control, and Audioengine A2's ... no problem. I feed them with optical out from a vintage Sony discman.
Thanks. Just curious, why will cable length not matter here? When does it matter then..?
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post #4 of 5
6/30/09 at 5:11am
Quote:
Originally Posted by backtoreality15 View Post
Thanks. Just curious, why will cable length not matter here? When does it matter then..?
It may matter...
Long cable lengths can possibly add too much capacitance to a passive volume control, which may cause high frequencies to be more subdued. This is because a passive volume control generally has a higher impedance than a driven line. Try it out and see if it's to your liking.
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post #5 of 5
7/2/09 at 1:24am
Well murrays is 100% right of course -- for long cables.

The standard advice for passive pre-amps is "keep the cable from the passive pre-amp to the amplifier short and of high quality", and indeed if there is a problem it will show up in the highs (since the cable load acts as a low-pass filter).

But you are talking about only 6 feet! That's less than 2 meters! Oh I guess some purists might say anything over 1 meter could be a problem, but the generally accepted wisdom is that 2 or 2.5 meters is still no problem. With a decent cable, you could go 2.5 meters, maybe even 3, without a high freq loss that you could hear. (Depends on the actual specs of the Passive Preamp).

Get your cables from Blue Jeans and you should have no issue at 6 feet.

Here's some reading:

How the passive preamps work

Very new article, specifically mentions 2 meters as OK:

Use a Passive Preamp For Excellent Sound Quality: Unamplified Volume Control Gives Low Cost Audiophile Performance | Suite101.com

With specs from Axiom and Blue Jeans you can actually work this out ... but I am sure 6 feet will be OK.
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