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Old 16th March 2006, 03:35 AM   #1
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Location: Flint, MI
Default Mono to stereo advice

I am trying to figure out a way to accomplish a seeming simply task. My car's headunit has an Aux input into it. I am connecting a mobile DVD player and a mobile VCR audio into this connection. The problem I have is that while the DVD has stereo out, the VCR only has mono out. I want to have the VCR's audio come through all of the speakers, not just the left or right side only. Since the radio only has one set of inputs, I am adding y adapters to be able to take in both devices. Normally I would just install a y adapter onto the end of the mono source and broadcast the signal over both l and r channels. THe problem I have now is that if I do this, when I hook in the DVD's stereo audio, it will be merged into a mono channel because of the VCR's y splitter. How can I convert the mono channel into 2 channels so that it will not allow this to happen? I can provide a drawing of the setup if that will make it easier to understand. Thanks!
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Old 16th March 2006, 11:11 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

its generally not a good idea to connect outputs together.

What you need is a mixer, it can be passive if you have spare gain.

A passive mixer will reduce stereo channel separation if one set
of inputs is monoed, the seperation left depends on details.

For an active mixer monoing one set of inputs will not matter.

/sreten.
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Old 16th March 2006, 11:47 AM   #3
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Location: Louisiana
You can use a 4 pole double throw relay to switch the signals. When the relay's coil is not energized, one source plays through. When the relay coil has power applied, the other source plays through. Since the sources are completely isolated, it doesn't matter if one is mono and the other is stereo.

You'll need to cut, strip and solder RCA patch cords (not the cables on the equipment) to the terminals. Use a relay socket in case the relay is defective or fails.

The power for the coil can be tapped off of virtually any switched power source and passed through a single pole single throw switch. Include a 1 amp fuse at the point where you make the connection to the power source. One coil terminal (A or B) will be grounded. The other terminal will get power from the switch. The switch will determine which source plays through.

If you get a 'pop' when switching sources, add the 100k ohm resistors as shown. They bleed off leakage from the capacitors in the signal line (inside the signal sources).

If you cannot find a 4pdt relay, use 2 dpdt relays like the Radio Shack 275-218.

Four sets of contacts are needed to keep the shields isolated as well as the signal lines. This helps prevent ground loops.
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File Type: gif signalswitcher01.gif (19.8 KB, 106 views)
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Old 16th March 2006, 03:37 PM   #4
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Ok, thank you very much! This sounds like what I was thinking. Since I have 2 video sources as well I am either going to get (3) DPDT relays or (1) 4PDT & (1) DPDP and wire up a switch to my dashboard to toggle between the 2 audio & video sources. Thanks again!
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Old 17th March 2006, 01:12 PM   #5
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I am trying to find the best relay for this. I have found a couple of options on ebay that I am not sure if they will do the trick. Any advice would be appreciated.

6PDT Relay

OR

4PDT Relay

The only other question I have concerns the 6PDT relay. Since the coil voltage is only 6-8vdc, what do I need to do to drop the 12v car power down to this range? It has been years since I have done any circuit design and I am a bit rusty. Thanks!
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Old 17th March 2006, 02:00 PM   #6
sreten is offline sreten  United Kingdom
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Location: Brighton UK
Hi,

I didn't realise that you wanted to use a switch.

In that case you simply need a double pole double throw switch.

The input is connected to the two centre pins L + R.

The sources are connected to the top two and bottom two pins L + R.

The mono source is connected to both pins.

e.g.

http://www.maplin.co.uk/Module.aspx?...=2341&doy=17m3


Click the image to open in full size.

/sreten.
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Old 17th March 2006, 02:12 PM   #7
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I actually like the relay idea a lot more. I already have a factory switch that is installed and not in use that I can re-wire to make it turn power on and off for the relays. I am trying to keep everything as simple as possible to use, and I think a 6PDT relay with the L, R, & Video signals would work best. I just need to know if the one that I can get on eBay would work for this and what I should do to lower the 12vdc down to the 6-8vdc that the relay requires. Thanks for the suggestion!
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Old 17th March 2006, 02:36 PM   #8
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Location: Louisiana
A series resistor would drop the voltage.

I strongly recommend that you use relays that have sockets. If you get a bad relay, you have to resolder all of the connections. If you have an intermittent problem and are not sure if it's a relay, a cable or something else, it's easy to swap relays that are in sockets. I've done it without sockets and changing a relay is time consuming. You won't pay much more at RS (where sockets are readily available).
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Old 17th March 2006, 04:14 PM   #9
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Join Date: Mar 2006
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The only problem with going to RS is that for a DPDT Relay, they want almost $10, where on eBay I can get the 6PDT for around the same price. I don't mind the soldering If I can save over $20 to make this. But I do agree that a socket is more convient. Thanks for the suggestion!
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