Hendrix Posted January 23, 2014 Report Share Posted January 23, 2014 Hi everyone, I want to build a TC Cable for the App Movie-Slate on the iPhone. After researching a bit got this document from Denecke: http://www.denecke.com/Support/Documents/Smart%20Device%20Input%20&%20Output%20Cables%20Schematic.pdf I want to build the type with a pad. But what I am wondering is what are the 1K resistor and the .022uF capacitor for? Propably some basic electronics trick, but I am relatively new to this and am curious Thanks in advance, Hendrik Smart Device Input & Output Cables Schematic.pdf Quote Link to comment Share on other sites More sharing options...
Boomboom Posted January 23, 2014 Report Share Posted January 23, 2014 Hi Hendrix, you don't need the capacitor, just use the resistors (33K and 1K) and it should be ok. As for what are these resistors for, I guess it's simply lowering the level on both L and R channels but couldn't confirm (my knowledge in electronics is laughable). I guess the capacitor is there to kind of regularize the level if it's to be used with a variable output TC unit ? More kind of a level "limiter"? Somebody could confirm... (?) I did a cable like this to use with my iPhone and the ToolBox app and it works fine. It's Charlie (Parra) who actually told me to lose the capacitor when I asked him about the cable schematics last year... Quote Link to comment Share on other sites More sharing options...
Hendrix Posted January 23, 2014 Author Report Share Posted January 23, 2014 Hi Pierre, thanks for the thoughts, in the meantime I already built the adaptor as shown in the picture. I will try it out tonight when I get access to the iPhone (it´s for a cam op friend of mine). I´m still curious what the capacitor actually does in this little schematic. Any electronics specialists on board? Quote Link to comment Share on other sites More sharing options...
brian albritton Posted January 23, 2014 Report Share Posted January 23, 2014 I believe the capacitor is there to block dc voltage on the mic input of the iPhone coming back into your timecode device. the resistors are there to pad the line level signal down to the mic input on the iPhone. Quote Link to comment Share on other sites More sharing options...
Hendrix Posted January 23, 2014 Author Report Share Posted January 23, 2014 Ok, so the capacitor is for blocking dc voltage, the 33k is for padding... what is the 1k resistor for? Gesendet von meinem C6903 mit Tapatalk Quote Link to comment Share on other sites More sharing options...
FredS Posted January 23, 2014 Report Share Posted January 23, 2014 The 33k + 1k resistors present a 34k load to the source. By tapping the output across only the 1k portion sends only 1/34th of the input voltage to the output. That arrangement is called a voltage divider. And as mentioned earlier the cap blocks DC from the Mic In (standard requirement for powering electret mics) from pushing that offset voltage back up into the source circuitry. Quote Link to comment Share on other sites More sharing options...
jason porter Posted January 23, 2014 Report Share Posted January 23, 2014 SCIENCE!! Quote Link to comment Share on other sites More sharing options...
Hendrix Posted January 23, 2014 Author Report Share Posted January 23, 2014 Cool, I think I got it... Thx Fred Gesendet von meinem C6903 mit Tapatalk Quote Link to comment Share on other sites More sharing options...
John Blankenship Posted January 24, 2014 Report Share Posted January 24, 2014 There seem to be a lot of people here who went to a different electronics school than I did. As illustrated, a circuit consisting of a 33k and a 1k resistor (and, yes, it is a voltage divider, if you wish to term it that way), you effectively have a 30dB pad. That depends, of course, upon the input impedance of the circuit you're feeding. If it's of a low impedance, the pad will attenuate more. The capacitor is likely there as an RF bypass. Blocking capacitors are wired in series with the signal lead, not in parallel as in this circuit. Wired in parallel, any D.C. voltage is still applied to the leads. Quote Link to comment Share on other sites More sharing options...
FredS Posted January 24, 2014 Report Share Posted January 24, 2014 Good catch on the cap, John. That's what I get for answering from my phone without the picture staring me in the face. Quote Link to comment Share on other sites More sharing options...
studiomprd Posted February 6, 2014 Report Share Posted February 6, 2014 Hendrix: " But what I am wondering is what are the 1K resistor and the .022uF capacitor for? " to make it work properly... Quote Link to comment Share on other sites More sharing options...
Hendrix Posted February 6, 2014 Author Report Share Posted February 6, 2014 Thx... Thats kind of obvious... Just trying to understand the electrical relations... Quote Link to comment Share on other sites More sharing options...
Matt Radlauer Posted February 6, 2014 Report Share Posted February 6, 2014 Dont mind the senator.. Thats what he does. We should call him Captain Obvious.. Quote Link to comment Share on other sites More sharing options...
Hendrix Posted February 6, 2014 Author Report Share Posted February 6, 2014 haha... thats what I figured Quote Link to comment Share on other sites More sharing options...
John Blankenship Posted February 7, 2014 Report Share Posted February 7, 2014 First, without figuring in the impedance of the circuit it's feeding, here's what's happening: The Denecke device (btw, Denecke Rocks!), applies its voltage across a 34k ohms load -- the 33k resistor plus a 1k resistor. The 33k ohm resistor drops 33/34th of the fed voltage, while the 1k resistor only sees 1/34th of it, which happens to be about a 30dB drop in level feeding the succeeding circuit. However, the input of the device being fed can change this equation. Here's an example of how: If the circuit you're feeding had (it's probably higher, but for the sake of illustrating the point) a 1k ohm impedance, then that 1k in parallel with the 1k resistor together are 500 ohms (or .5k if you prefer). The Denecke device is now feeding a voltage divider consisting of 33k and .5k which means that the load is fed 1/67th of the voltage, or approximately 36dB attenuation as compared to 1/34th which is about 30dB with 33k & 1k. The capacitor is likely there as an RF bypass component, to keep stray RF -- higher than audio frequencies -- out of the input. YMMV -- shipping charges may apply -- void where prohibited by law -- plus tax and re-cappable tires -- and don't let your spouse find out unless you've purchased a dazzling Valentines Day gift. Quote Link to comment Share on other sites More sharing options...
eombilod Posted February 16, 2014 Report Share Posted February 16, 2014 ooo just purchase the damn thing! hahah Quote Link to comment Share on other sites More sharing options...
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