TV's Optical Digital Video Out directly to Speakers?

Thread Starter

c627627

Joined May 18, 2011
47
This is just a project, I can actually connect the TV to receiver, but to learn how things work and as a fun project, I am interested in connecting the [EDIT] Optical Digital Audio Out from the back of my TV to these two speakers, directly. What gadget can I buy / make to accomplish that goal?

I just wanted to learn how this could be done directly from a Panasonic TC-P50U50 TV to these two 2.7Ω 7.5W speakers:

speakers.jpg
 
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Thread Starter

c627627

Joined May 18, 2011
47
Yes. I was actually getting exactly what you suggested so that I could use headphones on the optical audio (not video) TV out.

So then using exactly the same gadget you linked to, using the RED + WHITE RCA Composite outs,
1. What do I buy to go from RED+WHITE RCA Composite outs to pictured speaker wires and
2. Could you say a word or two on how these are 7.5W 2.7Ω speakers and on limits of those values if different speakers were used.
Thank you.
 

wayneh

Joined Sep 9, 2010
17,153
Yes. I was actually getting exactly what you suggested so that I could use headphones on the optical audio (not video) TV out.

So then using exactly the same gadget you linked to, using the RED + WHITE RCA Composite outs,
1. What do I buy to go from RED+WHITE RCA Composite outs to pictured speaker wires and
"Composite" is a video term. These are simple RCA audio jacks. You need an audio amplifier to take this line-level signal to headphones or speakers.
2. Could you say a word or two on how these are 7.5W 2.7Ω speakers and on limits of those values if different speakers were used.
Thank you.
Those are considered "loudspeakers" and have a relatively low input impedance. A headphone amplifier would not typically have enough power to drive them. You need a regular audio amplifier rated to drive speakers at that low impedance. You could use an amp that's capable of more that 7.5W, but there is always some risk when the amp can supply more power than your speaker can handle. The speaker begins to look like a fuse.
 

Thread Starter

c627627

Joined May 18, 2011
47
Is there a gadget that combines the two things you linked to into one gadget:
Optical Digital Audio INPUT and speaker wire OUTPUT?

In other words, must I use two devices if I wanted to do this on the cheap:
The first you linked to, to get Optical INPUT into RCA audio red and white cables cables
and then
Red and white cables to the second one you linked to, which would finally allow connection to speaker wire.


Also, when researching this I noticed that some boards may have an actual 3-Pin output, does that mean I could just use that 3-Pin connector that my speakers are connected to, as pictured in post #1 of this thread?
 
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Thread Starter

c627627

Joined May 18, 2011
47
Yes, of course.
But combining previously linked two +/- $10 gadgets would drive those speakers, and keep things affordable.
I thought there was something that combined them both in one, something priced as much or less than two of them combined?

Will there be volume control through TV remote using the two $10 gadget combo?

And I do see equivalents with their own Volume knob in the $15 range, but they claim 200W, not 10W like the & $10 gadgets.
I take it you would not recommend those because they are overkill for the pictured speakers in post #1?
 

crutschow

Joined Mar 14, 2008
27,476
They would likely work at normal listening levels, but could possibly overheat at higher volume levels.
For safety you could put a 1Ω, 2W resistor in series with each speaker to bring the total impedance up to a nominal 3.7Ω, which should be high enough to prevent the possibility of damage.

Note that some of those amps require a power supply, which likely could done with a properly sized wall wart.
Will there be volume control through TV remote using the two $10 gadget combo?
Depends upon whether your can set you TV so that the optical output level is controlled by the volume control.
You would find that somewhere in the audio setup menu.
 
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Thread Starter

c627627

Joined May 18, 2011
47
First of all, thank you for all the useful information. To test this, I connected the Optical Digital Audio Out from the back of my TV to my big receiver. Sure enough, the volume could *not* be controlled by my TV's remote.

So now, going back to initial suggestions, let me summarize how I understood your advice:

1. $7 device would convert sound from Optical cable from TV to RCA audio cables:

Optical2RCA.png

2. ... which would then be connected to this $10 item (to get RCA cables to Speaker cables):

RCA2Speakers.png 2Speakers.jpg


... And that would get sound which cannot be increased/decreased from the speakers, but out of curiosity how loud would that sound be?


Either way, I understand you were saying that in order to get sound control, instead of the above board I would need to get something like this:

4-8ohms.jpg


...but you were saying that I would need to get two 1Ω, 2W resistors in order to do that safely.

Could you tell me exactly where the resistors would go?
 
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Thread Starter

c627627

Joined May 18, 2011
47
Could someone hand draw on the picture below where this 1Ω, 2W resistor would go?
Could you also say if price is the same, would it be better to go with higher/lower values and get a different, better resistor?

ResistorOnSpeaker.jpg
 

crutschow

Joined Mar 14, 2008
27,476
Could someone hand draw on the picture below where this 1Ω, 2W resistor would go?
You remove the wire from one terminal of the speaker.
Solder one end of the resistor to this terminal.
Solder the wire to the other end of the resistor.
That's what "in series" means.
Could you also say if price is the same, would it be better to go with higher/lower values and get a different, better resistor?
You need a 1Ω, 2W resistor, not one higher or lower.
What is "better"?
 

Thread Starter

c627627

Joined May 18, 2011
47
If the speaker is a 2.7Ω, 7.5W speaker, then using a 1Ω, 2W Resistor would make it a 3.7Ω speaker?
Then wouldn't using a 2Ω, 2W resistor be "better" because instead of a 3.7Ω speaker, you would have a 4.7Ω speaker, which would be fully within specs of required speaker impedance of 4Ω to 8Ω?

Is this the solution:

Solution.jpg
 

crutschow

Joined Mar 14, 2008
27,476
Then wouldn't using a 2Ω, 2W resistor be "better" because instead of a 3.7Ω speaker, you would have a 4.7Ω speaker, which would be fully within specs of required speaker impedance of 4Ω to 8Ω?
A 2Ω resistor would further reduce the power to the speaker and require a higher wattage resistor.
The 4Ω lower limit for the amplifier is somewhat arbitrary so I'm reasonably sure that 3.7Ω won't hurt it.
Using a 1Ω resistor is a compromise between being sufficiently close to the amplifier's limit without too much power reduction to the speaker.
It it makes you feel better you could use a 1.5Ω resistor to give a 4.2Ω speaker.
For that the resistor should be 1.5Ω, 4W.

Your diagram looks correct.
 

Thread Starter

c627627

Joined May 18, 2011
47
Great. Thank you very much, crutschow.

Feelings have nothing to do with it, just trying to learn what's ideal.
Twenty 1Ω, 2W resistors are $1.32 but I cannot find 1.5Ω, 4W resistors on eBay or anywhere else close to that price.

[I thought they were the same price, but that was for a 1.5Ω, 2W resistor and we need a 4W to come out ahead...]

But this is what I was looking at to buy:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=192110360602
 
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crutschow

Joined Mar 14, 2008
27,476
Those should be fine.

Note that you can get close to the ideal value of 1.3Ω, 4W to give a 4Ω speaker, by using two 2.7Ω, 2W in parallel which gives 1.35Ω, 4W.
You connect those two parallel resistors in series with the speaker leads as you showed.

You can even get the ideal value by using three, 3.9Ω in parallel, giving 1.30Ω, 6W. :D
 

Thread Starter

c627627

Joined May 18, 2011
47
Okay. Can you tell me how to connect them and what the real life vs. theoretical advantage is compared to our original plan?
 
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