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Old 16th December 2010, 05:43 PM   #1
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Default iPod/BlackBerry/MP3 input

Hello everyone,
If designing an input for an iPod/BlackBerry/MP3 player, should I use an "R" or a "C" and what value would you think? Everything that I have found online states these players use 32 ohm headsets, thus the 33 ohm resistor, and that the max power out is 30mW. Doing the math, that's around a volt.

Thanks,
Ray
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Old 16th December 2010, 06:07 PM   #2
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by rsumperl View Post
Hello everyone,
If designing an input for an iPod/BlackBerry/MP3 player, should I use an "R" or a "C" and what value would you think? Everything that I have found online states these players use 32 ohm headsets, thus the 33 ohm resistor, and that the max power out is 30mW. Doing the math, that's around a volt.

Thanks,
Ray
For interest you do not need the 33 ohm resistor to "load" the Ipod. What ever has been used at the input is fine. However the output from the H/P socket is not as good as the Ipod connector output. So a charge lead with audio out is better. It does not have a volume control so the input from the Ipod needs to go into a volume control. Many will argue that direct in with no cap is best, however I do like to have cap isolation to something you may hold in your hand. 1uF paper or polyprop works well!

Take a look here:
ipod nano dock


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M. Gregg
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Old 16th December 2010, 06:55 PM   #3
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My thought was to have a 3.5mm jack so that I could use a 3.5mm to 3.5mm cable. I thought that would be more "universal" whether I use an iPod/MP3 player or a BlackBerry.
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Old 16th December 2010, 07:16 PM   #4
M Gregg is offline M Gregg  United Kingdom
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Originally Posted by rsumperl View Post
My thought was to have a 3.5mm jack so that I could use a 3.5mm to 3.5mm cable. I thought that would be more "universal" whether I use an iPod/MP3 player or a BlackBerry.
I have done what you describe, you just need to connect it as any other input only using the 3.5 socket. It works OK. However I wanted to charge the Ipod as well when in use. Forget the H/P load and connect as normal with a 1uF input cap for safety!
You could just use a lead with 3.5mm plug to 2 phono plugs and connect them to any input!<<< I now know this is better because there is no chance of shorting the Ipod H/P out when you connect to the socket, however this is short protected!

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M. Gregg
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Old 16th December 2010, 07:42 PM   #5
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I assume the "units" would like to see a load for proper audio response. That's why I thought of the 33 ohm resistor.
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Old 16th December 2010, 11:39 PM   #6
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For maximum voltage transfer you want a load impedance significantly higher than the source's output impedance. Equal impedance is for maximum power transfer which is not your concern in this case.
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Old 16th December 2010, 11:59 PM   #7
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I assume the "units" would like to see a load for proper audio response. That's why I thought of the 33 ohm resistor.
Your looking for maximum voltage transfer rather than maximum power transfer. Putting in a 33 ohm resistor will lose a considerable amount of voltage.

A normal system with a mixer and amplifier has a mixer output impedance of a few ohms while the amplifier will typically have an input impedance of 47K.
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