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Message |
Guest
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 Posted:
Sun Oct 16, 2005 9:21 pm Post subject:
Stereo headphone jack to mono RCA audio |
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I want to connect the stereo headphone jack on a laptop computer to a
mono RCA audio jack on a television and get both the R and L sound from
the laptop mixed to mono out of the television speakers. Also, the
laptop and television are about 20 feet apart. What is the right way to
do this?
Regarding the 20 foot cable I will need between the laptop and the
television, I was thinking I could connect two 10 foot RCA cables
together to get the distance. I know that for RCA composite video this
would not work since the cables are designed to have a specific
resistance (I think), so connecting two in series would double the
resistance then it wouldn't work correctly. But will connecting RCA
cables in series work for audio?
-Jonathan
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Harry Lavo
Guest
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| Posted:
Sun Oct 16, 2005 9:59 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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<jfklein@shaw.ca> wrote in message
news:1129479694.721665.314780@o13g2000cwo.googlegroups.com...
| Quote: | I want to connect the stereo headphone jack on a laptop computer to a
mono RCA audio jack on a television and get both the R and L sound from
the laptop mixed to mono out of the television speakers. Also, the
laptop and television are about 20 feet apart. What is the right way to
do this?
Regarding the 20 foot cable I will need between the laptop and the
television, I was thinking I could connect two 10 foot RCA cables
together to get the distance. I know that for RCA composite video this
would not work since the cables are designed to have a specific
resistance (I think), so connecting two in series would double the
resistance then it wouldn't work correctly. But will connecting RCA
cables in series work for audio?
-Jonathan
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Yes, two 10's connected will do fine. Why not a 20'? Coming out of the
laptop you need a stereo-mini-plug to dual RCA adaptor cable. Radio Shack
carries these. So with one of these and two 10' cables, you would simply
need an additional two RCA-to-RCA connecting adaptors, again at Radio Shack.
Resistance or capacitance will not be an issue with standard phone cables.
I've done similar things...never had a problem. |
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Richard Crowley
Guest
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| Posted:
Mon Oct 17, 2005 12:27 am Post subject:
Re: Stereo headphone jack to mono RCA audio |
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jfklein wrote ...
| Quote: | I want to connect the stereo headphone jack on a laptop computer to a
mono RCA audio jack on a television and get both the R and L sound
from
the laptop mixed to mono out of the television speakers. Also, the
laptop and television are about 20 feet apart. What is the right way
to
do this?
Regarding the 20 foot cable I will need between the laptop and the
television, I was thinking I could connect two 10 foot RCA cables
together to get the distance. I know that for RCA composite video this
would not work since the cables are designed to have a specific
resistance (I think), so connecting two in series would double the
resistance then it wouldn't work correctly. But will connecting RCA
cables in series work for audio?
|
Yes, connecting the cables in series will work for both video
and for audio. Neither audio nor video cables should have
any significant "resistance" Video cables should be designed
for 75-ohm impedance, but that doesn't change with distance,
(even many miles) and for short distances even that isn't critical.
You need a cable or adapter from stereo mini-phone to a
pair of RCA connectors, and then an RCA "Y-adapter" to
make mono out of the signals. With decent (but not "premium"
expensive) cable, doing this over 20 feet should be no real
problem.
Note that you may have to deal with isolation or shielding/
grounding issues from the laptop, but this has nothing to do
with the stereo/mono or the distance. |
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Tomi Holger Engdahl
Guest
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| Posted:
Mon Oct 17, 2005 4:31 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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jfklein@shaw.ca writes:
| Quote: | I want to connect the stereo headphone jack on a laptop computer to a
mono RCA audio jack on a television and get both the R and L sound from
the laptop mixed to mono out of the television speakers. Also, the
laptop and television are about 20 feet apart. What is the right way to
do this?
|
The right way to this is to take 6 feet 3.5 mm stereo plug to
two RCA connectors cable. And then add the following circuit
(you have to build it yourself, no recommendation where to buy ready maade)
between the two RCA connectors and one RCA connector on the TV.
http://www.epanorama.net/circuits/linesum.html
To build this circuit you need three RCA connectors and two 10 kohm
resistors (R1 and R2). The resistors connect the audio signals (center
connector) from inputs together to from one output signal. You can see
the wiring details in the figure below:
INPUT 1 -------\/\/\/\---+
---+ R1 10K +------------ OUTPUT
| | +----
INPUT 2 -------\/\/\/\---+ |
---+ R2 10K |
| (shields) |
+---------------------+
When you have connected the audio lines together using the resistors,
then connect the connect the connector grounds directly together using
short piece of wire. Now you have made a nice one channel mixer
circuit which can mix together two line level audio signal sources.
| Quote: | Regarding the 20 foot cable I will need between the laptop and the
television, I was thinking I could connect two 10 foot RCA cables
together to get the distance.
|
It is possible. But it should not be too hard to find ready made
20 foor cable. I can myself find 10 meter cables from computer and
audio shops without problems...
Hooking up two RCA cables after each other can work also work,
but with low quality cable connectors and/or RCA female-female
adapters this joining of two cables can be unreliable.
| Quote: | I know that for RCA composite video this
would not work since the cables are designed to have a specific
resistance (I think), so connecting two in series would double the
resistance then it wouldn't work correctly.
|
Joining two cables will work for composit video and other
video signals as well. The video cables are designed to have a
specific impdance for the high frequency video signal travelling
with the cable. This cable impedance is something diffent
than the resistance you measure with a multimeter.
When you have a video cable that has 75 ohm impedance is always
75 ohm for the signal no matter how long the cable is.
When you take 75 ohm cable from the cable spool to make
cable, you can cut any length of the cable and the
results is 75 ohm transmission line. And you can join
together two pieces of 75 ohms cables, if the connection
is done well it is practicallyu same as one long pice of
75 ohm cable.
| Quote: | But will connecting RCA cables in series work for audio?
|
Connecting RCA cables in series will work nicely.
No problems as long as you do the connection reliably
(so that the cables make good reliable connection).
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
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Guest
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| Posted:
Mon Oct 17, 2005 7:46 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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Thanks to all who replied, very good information.
I have another question on this.
Instead of using "RCA cable" (ie: cable that is specifically designed
for conecting to the RCA inputs on a television), can I use speaker
cable (the cable with black and red connectors)? The connectors on
speaker cable physically fit on the RCA connectors but I am concerned
that the cable might not have the correct design, in particular the 75
ohm impedance.
-Jonathan
jfklein@shaw.ca wrote:
| Quote: | I want to connect the stereo headphone jack on a laptop computer to a
mono RCA audio jack on a television and get both the R and L sound from
the laptop mixed to mono out of the television speakers. Also, the
laptop and television are about 20 feet apart. What is the right way to
do this?
Regarding the 20 foot cable I will need between the laptop and the
television, I was thinking I could connect two 10 foot RCA cables
together to get the distance. I know that for RCA composite video this
would not work since the cables are designed to have a specific
resistance (I think), so connecting two in series would double the
resistance then it wouldn't work correctly. But will connecting RCA
cables in series work for audio?
-Jonathan |
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Guest
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| Posted:
Mon Oct 17, 2005 7:49 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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Richard Crowley wrote:
<snip>
| Quote: | Note that you may have to deal with isolation or shielding/
grounding issues from the laptop, but this has nothing to do
with the stereo/mono or the distance.
|
Can you clarify this? How would I shield or ground my laptop?
-Jonathan |
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Richard Crowley
Guest
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| Posted:
Mon Oct 17, 2005 8:09 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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<jfklein@shaw.ca> wrote ...
| Quote: | Thanks to all who replied, very good information.
I have another question on this.
Instead of using "RCA cable" (ie: cable that is specifically designed
for conecting to the RCA inputs on a television), can I use speaker
cable (the cable with black and red connectors)? The connectors on
speaker cable physically fit on the RCA connectors but I am concerned
that the cable might not have the correct design, in particular the 75
ohm impedance.
|
Forget about the 75 ohm impedance. It is completely
irrelevant to your situation. Maybe we didn't make
that clear enough?
No, you cannot use "speaker cable" because it is not
shielded. It has the two parallel wires (black & red)
instead of a single larger round cable which has one
wire inside with a shield all around it. |
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Richard Crowley
Guest
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| Posted:
Mon Oct 17, 2005 8:12 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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jfklein wrote ...
| Quote: | Richard Crowley wrote:
Note that you may have to deal with isolation or shielding/
grounding issues from the laptop, but this has nothing to do
with the stereo/mono or the distance.
Can you clarify this? How would I shield or ground my laptop?
|
When you get everything hooked up properly you will see
soon enough if you have a shielding/grounding problem or
not. No way to predict this.
If you have hum/buzz/etc. the first thing to try is to disconnect
the plug-in power supply/battery charger. This usually cures
the problem. But if you need to run your setup with the wall
power plugged in, come back here and we will help you. |
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Guest
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| Posted:
Tue Oct 18, 2005 7:55 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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Richard Crowley wrote:
| Quote: | If you have hum/buzz/etc. the first thing to try is to disconnect
the plug-in power supply/battery charger. This usually cures
the problem. But if you need to run your setup with the wall
power plugged in, come back here and we will help you.
|
Ok, I've hooked the system up and I am indeed getting a slight buzz out
of the television speakers. Unfortunately I need to run with the laptop
plugged in since the battery is no good. So what can I do to elliminate
the buzz?
-Jonathan |
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Richard Crowley
Guest
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| Posted:
Tue Oct 18, 2005 8:09 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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jfklein wrote ...
| Quote: | Richard Crowley wrote:
If you have hum/buzz/etc. the first thing to try is to disconnect
the plug-in power supply/battery charger. This usually cures
the problem. But if you need to run your setup with the wall
power plugged in, come back here and we will help you.
Ok, I've hooked the system up and I am indeed getting a slight buzz
out
of the television speakers. Unfortunately I need to run with the
laptop
plugged in since the battery is no good. So what can I do to
elliminate
the buzz?
|
Then you likely need an isolation transformer of some kind.
The most easily availble is the Radio Shack # 270-054 |
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Guest
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| Posted:
Wed Oct 19, 2005 7:10 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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| Quote: | No, you cannot use "speaker cable" because it is not
shielded. It has the two parallel wires (black & red)
instead of a single larger round cable which has one
wire inside with a shield all around it.
|
Why does the cable need to be shielded? Usually the speaker jack on the
laptop is used for connecting small computer speakers or headphones and
I don't think either of these use shilded wires. Is there something
different about connecting the to an RCA input on a television that
requires using shielded cables?
-Jonathan |
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Richard Crowley
Guest
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| Posted:
Wed Oct 19, 2005 8:49 pm Post subject:
Re: Stereo headphone jack to mono RCA audio |
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jfklein wrote...
| Quote: | No, you cannot use "speaker cable" because it is not
shielded. It has the two parallel wires (black & red)
instead of a single larger round cable which has one
wire inside with a shield all around it.
Why does the cable need to be shielded? Usually the speaker jack on the
laptop is used for connecting small computer speakers or headphones and
I don't think either of these use shilded wires. Is there something
different about connecting the to an RCA input on a television that
requires using shielded cables?
|
If there is an amplifier at the destination end of the wire, you
likely need a shielded wire. Headphones and speakers don't
need shielded cable because there are no more amplification
steps in the chain.
But the wire that goes between your computer and your computer
speakers (IF they are "powered" speakers) is most likely shielded.
The reason is that the amplifier will amplify the noise along with
the signal if the wire is not shielded. The RCA input on your TV
goes through an amplifier before going to the speakers. You have
already discovered that it amplifies noise along with the signal even
if you DO have shielded cable. It would likely be MUCH worse
if you used unshielded cable. |
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