iPod/BlackBerry/MP3 input
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rsumperl
diyAudio Member

Join Date: Oct 2009
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
Attached Images
 Input Circuit.jpg (88.3 KB, 90 views)

M Gregg
Account disabled at member's request

Join Date: Jun 2010
Location: UK
Quote:
 Originally Posted by rsumperl 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

Regards
M. Gregg

Last edited by M Gregg; 16th December 2010 at 07:09 PM.

 16th December 2010, 07:55 PM #3 rsumperl   diyAudio Member     Join Date: Oct 2009 Location: Cascade, Idaho 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.
M Gregg
Account disabled at member's request

Join Date: Jun 2010
Location: UK
Quote:
 Originally Posted by rsumperl 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!

Regards

M. Gregg

Last edited by M Gregg; 16th December 2010 at 08:26 PM.

 16th December 2010, 08:42 PM #5 rsumperl   diyAudio Member     Join Date: Oct 2009 Location: Cascade, Idaho I assume the "units" would like to see a load for proper audio response. That's why I thought of the 33 ohm resistor.
 17th December 2010, 12:39 AM #6 mashaffer   diyAudio Member   Join Date: Jun 2004 Location: Indiana 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. __________________ Generic Signature
nigelwright7557
diyAudio Member

Join Date: Apr 2008
Location: Carlisle, England
Quote:
 Originally Posted by rsumperl 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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