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Old 11th April 2008, 11:21 AM   #1
robmil is offline robmil  United Kingdom
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Join Date: Jun 2004
Location: London
Default Joshua Tree with CD player

Hi all

I'm thinking of using a joshua tree attenuator but am failing to grasp the concept and application.

I have a CD player and it's output is a 2.2uf capacitor followed by a 100K resistor to ground. Will I get bass rool off?

Does the current standard JT 'mimmick' a 100K or 50K pot so the signal is 100K or 50K 'away' from gound or what?

I'm missing something aren't I

R
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Old 11th April 2008, 05:09 PM   #2
rellum is offline rellum  France
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Join Date: Jul 2004
Location: ALSACE
Hi Rob

From a resistance point of view, the tree attenuator doesn't act like a pot.
A pot has a constant input resistance and varying output resistance. A JT has a varying input resistance and constant output resistance.
JT's minimum input resistance=1.8K (-63.5dB) and max=30.5K (-32dB) with the standard values offered by Pear's Audio. It's way too low for you and the corner frequency will be 40Hz. Higher resistor values can be used, but then you will have an issue at your amp's input. A solution would be to add a buffer between the source and the JT, but it must have low dc offset to minimize switching noise.

I bought one kit recently, it's nicely done, but I still found no time to build it.

Cheers,
Francis
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Old 11th April 2008, 05:46 PM   #3
rellum is offline rellum  France
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Attached txt file with Rin and Rout for each setting.
Attached Files
File Type: txt jt_att.txt (9.0 KB, 15 views)
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Old 12th April 2008, 07:51 AM   #4
robmil is offline robmil  United Kingdom
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Thanks for that.

I had a feeling that was the case.

R
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