Question for soldering master...

[Pixel_Outlaw]

So, I have seen many AV selectors and want to make my own. These are also called switch boxes. This is a device that allows the user to connect X many AV inputs and then use a switch to select which one to output.

If you are still following me, my idea is to make one for those RCA composite video cables. Now, each complete set of cables has a channel for right audio (RED), left audio (white or black) and finally the video (yellow). I was hoping to use a multi position rotary switch for each of the three channels. This would mean that I set all three dials to the same position to select which AV group to use. My question is which kind of switch I would need to purchase and also, how to connect the positive and negative wires. My ideal setup would use 3 eight position switches allowing for 8 devices to be selected from. (I have 9 consoles hooked up to one television currently with some store bought AV switches daisy-chained together.)

For the sake of simplicity and to maximize number of possible devices I separated each "channel" into the switch. My question is how to hook up the positive and negative wire coming from each RCA jack to the switches and output cluster of RCA jacks.

A ROUGH image of what I would like to do.

[Voixdelion]

I'm not sure I understand the setup  - you have 3 switches?  Potential to choose the a combo of video and right and left audio?  Why would you not treat the audio as a pair?  



At any rate, i believe the RCA jacks are essentially the two + and - signal in one cord with two contacts.  The + would be the signal contact and the pointy plug part of the connector while the - would be the ground signal line (which is also used as a shielding for the + signal along the cord) and uses the round outside part of the plug.  So your outer ring on the jack contact would be - to switch and the plug contact the + to switch.  As to how the switch itself would operate, have you peeked inside any of the others you have daisy chained together?  Are they A/B switches only where you only have a choice of two or is a "push the button of the one you wish to be connected"   type?  If I were building one I would think that would be easier ...   Is that what you mean?

[Pixel_Outlaw]

I'm not sure I understand the setup  - you have 3 switches?  Potential to choose the a combo of video and right and left audio?  Why would you not treat the audio as a pair?  



At any rate, i believe the RCA jacks are essentially the two + and - signal in one cord with two contacts.  The + would be the signal contact and the pointy plug part of the connector while the - would be the ground signal line (which is also used as a shielding for the + signal along the cord) and uses the round outside part of the plug.  So your outer ring on the jack contact would be - to switch and the plug contact the + to switch.  As to how the switch itself would operate, have you peeked inside any of the others you have daisy chained together?  Are they A/B switches only where you only have a choice of two or is a "push the button of the one you wish to be connected"   type?  If I were building one I would think that would be easier ...   Is that what you mean?

Thanks for the help. I understand now how to wire each RCA end but I am still a bit unsure how to use the switch and what kind I need. Sadly, the store bought RCA selector has one way locking tabs that can not be opened without breaking the housing. I can't get at the innards to see how they wired them. I never really took any electrical classes in highschool my drawing was just sort of a crude treatment for how the outside should look. The actual wiring is still a bit of a mystery to me.


I just ordered some *ahem* sockets.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290443130971&ssPageName=STRK%3AMEWNX%3AIT

Now the question will be how many ports can I use without loosing picture quality from all the wiring...

[Voixdelion]

Are you still needing guidance on this?   If necessary I can show you a diagram of how to wire up those "*ahem* sockets" but in truth the switch will be basically a bridge with one fixed end to the same socket on the output side.  The other end of the bridge is the selectable part that connects to the desired input.  It really doesn't matter which is which as far as positive and negative provided that both points connect to the same both points on either side of the switch - unless you choose to only make the switching between the actual signal and make the grounds common in which case:


As far as switch type, I would imagine you are looking for something like this:  (though it has 12 positions - you would wire each incoming + to one of the selectable positions around the outer edge and the outgoing  + will be the center contact.  You can stick your own knob on the pin as design and aesthetics require )
http://www.elma.com/Admin/ProductionFiles1//ProductTypeFile/290/English/12%20Selector%20Switch%20Type%2001.pdf

Your switch if you use only the + signal while making the - a common ground will be a SINGLE POLE switch, with a minimum of 8 (your number of inputs) THROWS  - look for abbreviations like SPDT (Single pole double throw = 1 signal type two positions selectable) or 1P16T (1 pole 16 throw = 1 signal type with up to 16 positions selectable)  Alternatively if your switch will select both the - signal and + signal from each input you will want a Double POLE (DP or 2P) switch with 8 THROWS (or more if you want room to grow) but that will require two layers of pcb which I don't THINK is necessary for your application.  I believe you can wire all the - poles together as a common ground as this is often what I see on the pcb boards of tvs and av equipment in general. (anyone please correct this if I am mistaken)

As I understand it, and As ripster said you will want a "shorting" type  switch, called "make before break", because it makes contact  before it breaks contact so it doesn't POP with a burst as you  switch inputs but will have signal crossover as you move between them.  The non-shorting variety will have a no-contact position  in between selected inputs (no short=open) so will register a "pop" or  "burst" as you move between the possible inputs (which could damage the  speakers?).

EDIT> Whoops - Ripster recommended "break before make" or rather the "non- shorting" variety.  I don't know now which is proper, but will do some research as I am now curious about this myself and let you know what I find...  

That what you needed?

[Voixdelion]

according to this site:http://myweb.tiscali.co.uk/nuukspot/decdun/gainclonepre.html
   
    Source selector (for beginners).
Some people only ever use one source, usually CD but if you use more than one source then you will want to be able to select between each of those sources. This is most often done using some sort of switch. There is a much more complicated method using relays that I will leave for another time.
    The rotary switch is useful for switching more than two sources. If you have just two sources, then an ordinary DPDT toggle switch will take up much less room. I used one of these in my 'pod pre amp' to save on space but usually I use the rotary type.


DPDT selector switch.

Wiring A="Left channel source 1, B right channel source 1, C left channel out, D right channel out, E left channel source 2, F right channel source 2.
    Rotary types come in different configurations that allow you to switch a different number of sources. If you have, say three sources to switch, a 4 pole 3-way switch will do the job and enable you to switch both 'hot' and 'cold' lines at the same time (for two channels).     Hot and cold lines - the 'hot' line is the wire carrying the signal. The one that you connect to the centre pin of the phono plug/socket. The 'cold' wire carries the return signal to ground.


Rotary selector switch.
Wiring depends on switch type
If you need to switch between more than three sources, use a 2 pole 6-way rotary switch. This would allow you to switch up to six sources for two channels but only on the 'hot' line and not the 'cold'.
    Another option is to make your own rotary switch from a switch mechanisms and rotary wafers (use the break-before-make type also called 'non-shorting'). However, ready-made switches are cheaper and sealed!
               
Though I did find another source that recommended the shorting type in audio applications, I couldn't get photos without registering so not sure if that is applicable.

[Voixdelion]

further research indicates that the shorting vs non-shorting issue is largely dependent on whether you are switching both the + -  simultaneously (via a double pole switch) or whether you are just switching the +/hot/signal and tying the grounds at the input.  I'm not sure exactly which one is desirable for each though.  See this discussion here:
http://tubehifi.websitetoolbox.com/post?id=352058
There is some general consensus that the last statement on the page is the basic difference between shorting and non-shorting switches, where shorting essentially keeps input constant, but this discussion indicates that some fuzziness may exist in terms of whether people are meaning shorting 2 inputs together or shorting 1 input to ground, and whether or not volume attenuation is involved as a factor which would account for the discrepancies in opinion of what is proper.  The company (elma) reply to that question says never short two inputs (presumably to 1 ground) and also specifically state that input selector type should be NON-shorting , so it seems that :

Unless you have issues with ground looping noise (which is apparently easily solved by turning off any component not currently in use anyway), it is probably simpler for your application to tie the grounds together as well as to the case itself for additional shielding, and use  a non-shorting break before make variety single pole 8(or more) throw switch to which you would wire each incoming + signal to the outer ring of contacts on the switch and the outgoing + signal to the center point, but you could use a 2P8+T switch (NON-shorting) and also switch the ground - which may be more desirable as it might be easier to find a 2P switch with that many throws than a 1P switch.  In any case, the elma company is apparently a good place to shop for such a thing and offer both shorting and non shorting varieties of either 1P or 2P switches with enough throws for your purpose.  http://www.elma.com/Americas/English/Products/RotarySwitches_4/SelectorSwitches_30.aspx

Additional sources from which I concluded all of the above:
http://www.diyaudio.com/forums/everything-else/93311-wiring-rotary-selector-switch-2.html
http://www.tnt-audio.com/accessories/switch_audibility_e.html
http://www.doctronics.co.uk/gt_4.htm#rotary (excellent explanation of pole and throw here)
http://www.head-fi.org/forum/thread/419015/rca-source-selector-switch-box-again

Hope that was of some help and not adding to your confusion.  Good luck.

[Pixel_Outlaw]

Thanks, since the original post I gathered all my parts and they are now in the mail. I'm using 3, 12 way switches (cheaper than a single switch), I've decided on 12 device inputs with a single output. I'm using speaker wire to wire the thing together.

Switches
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260617124947&ssPageName=STRK:MEWNX:IT

RCA clusters

[Voixdelion]

okay - for these then the +ins are around the circumference and the + output line is the center contact or some other obvious solderable  point that isn't one of the inputs.  you wire the -'s together and ground to the case (and the output - goes to the ground as well.)
Not too difficult! Let us know how it turns out, I might do this myself now too.  If you want to get really fancy you can buy pcb kits and etchant at radio shack - or maybe some of that rear window defroster repair stuff discussed here (if its copper, should work beautifully):http://geekhack.org/showthread.php?t=10723&goto=newpost