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Small problem with new DIY ipod Dock

post #1 of 4
3/28/08 at 1:31pm
Thread Starter 
I just made an ipod charging/line out dock (you can see it here http://www.head-fi.org/forums/f6/pos.../index312.html) with +5v going to pin 23 and common going to pin 16(pinout here Apple iPod dock interface pinout and signals @ pinouts.ru ) . This is sent through a switch so that I can turn the voltage on and off.

When using the line out with the +5 volts, there is a high pitched buzzing noise present. It isn't particularly noticeable unless I turn the volume up a good amount on my amp/receiver, but it definitely stops once I take away the +5v.

What would you recommend? The chassis is obviously well grounded, but perhaps I need to use a DC powersupply with a ground instead of just a 2 prong plug. Or maybe a ferrite core could help?

What about the supply voltage, is this the wrong place to send voltage for my purpose?

Any comments would be appreciated.

A friend just told me to try and isolate the audio ground from the chassis, sounds like it could be the answer.
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post #2 of 4
3/28/08 at 2:21pm
I would agree with your friend; that power jack looks to be the type that has the negative connection go through the outside of the jack. This means that you have voltage going through the ground connection on your rca jacks. while isolating the rca jacks would probably solve your problem, I would get an isolated dc jack. Actually, I would proably do both... but I am limited in my knowledge of how grounding should be done in an audio project.

EDIT: looking at the inside pics confirms what I thought; the negative of the jack is connected to the case, as are your rca grounds. I would start with isolating one or the other, whichever is easier for you, then trying the other if that doesn't work.
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post #3 of 4
12/24/09 at 1:46pm
Quote:
Originally Posted by Punnisher View Post
I just made an ipod charging/line out dock (you can see it here http://www.head-fi.org/forums/f6/pos.../index312.html) with +5v going to pin 23 and common going to pin 16(pinout here Apple iPod dock interface pinout and signals @ pinouts.ru ) . This is sent through a switch so that I can turn the voltage on and off.

When using the line out with the +5 volts, there is a high pitched buzzing noise present. It isn't particularly noticeable unless I turn the volume up a good amount on my amp/receiver, but it definitely stops once I take away the +5v.

What would you recommend? The chassis is obviously well grounded, but perhaps I need to use a DC powersupply with a ground instead of just a 2 prong plug. Or maybe a ferrite core could help?

What about the supply voltage, is this the wrong place to send voltage for my purpose?

Any comments would be appreciated.

A friend just told me to try and isolate the audio ground from the chassis, sounds like it could be the answer.
did you ever figure this out, I just made a ipod dock and would like to add charging to it. any ideas, what voltage, I am assuming 5v, but i have seen where there is a 10k resitor needed?
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post #4 of 4
12/24/09 at 3:27pm
Thread Starter 
I used the 5v input for USB, which worked well for me and my 5g ipods. Strangely, the 80gb classic (first run of classics) played audio just fine but would not charge. You need to take that into consideration before making yours. There are other pins and configurations that will likely work with all ipods.

I ended up isolating the rca output jacks from the chassis. I cannot remember if that cured the buzzing problem. I still use the dock for playback and charging at work but the noise is so faint that it's not worth worrying about.
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