Joshua Tree with CD player

robmil · 11th April 2008, 11:21 AM

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

rellum · 11th April 2008, 05:09 PM

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

rellum · 11th April 2008, 05:46 PM

Attached txt file with Rin and Rout for each setting.

robmil · 12th April 2008, 07:51 AM

Thanks for that.

I had a feeling that was the case.

R

11th April 2008, 11:21 AM	#1
robmil diyAudio Member Join Date: Jun 2004 Location: London	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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11th April 2008, 05:09 PM	#2
rellum diyAudio Member 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

12th April 2008, 07:51 AM	#4
robmil diyAudio Member Join Date: Jun 2004 Location: London	Thanks for that. I had a feeling that was the case. R

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