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Hi guys,
I want to use a JT with my Squeezebox but have some concerns about the output and input impedances of the SB3 and JT respectively.
I found a Stereophile review where they measured the output impedance of the SB3 to be between 223Ohms and 549Ohms. If the input impedance of the JT has a minimum of 2k2Ohms then will I not have a problem? Shouldn't the ratio of out:in be greater than 10 in an ideal world? 549:2k2 is only 4.
Thanks, Shareef.
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Rank: Administration
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No worries using the squeezebox at all. Because the JT is purely passive all that will happen is you will get a bit more attenuation. Maybe 1db. I have actually used this configuration while testing. It works fine and sounds good.
I imagine the output impedance of the SB is high because they apply passive post filtering after the actual output. In any case it should not present a problem.
Cheers!
Russ
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Rank: Administration
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Joined: 10/24/2006(UTC)
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One other note. If you know the approximate output impedance of your source you can adjust(or even jumper) R1A&B if you want to maintain the same impedance curve. :) So if you have a source with 768R output impedance (or close) you could just jumper it. In your case you could reduce it by some value between 221 and 549. 392 would be a good guess. :) Cheers! Russ Edited by user Thursday, March 26, 2009 7:35:31 AM(UTC)
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Rank: Member
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Location: Cambridge
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Thanks for that Russ. Can I just check something. Why do you say 768R in your last post? I was using the calculator here: http://jos.vaneijndhoven...witchr/switchdesign.html and get a value of 794R for R1 when using the ideal input impedance of 0R, 750R output impedance and an attenuation of 0.5dB. Are these not the values you used when calculating for the JT? The closest E96 value is 787R. Cheers.
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Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
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Was thanked: 89 time(s) in 83 post(s)
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No they are not the same values. I have my own application for calculating the values which works a bit differently. :)
You have a complete parts list and a schematic. Work from that and you will be in good shape.
Of course its also fine to use your own calculated values and get whatever output impedance you choose.
Cheers!
Russ
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