how to put a signal level tap on my television's speakers?

[wsemajb]

Basic question is.... what devices/parts do I need inline with a speaker level output to drop it to signal level (ie, appropriate for use with aux inputs on an amplifier)? I also want to be highly confident that such use will not harm or put excessive load on the originating amplifier.

The longer story is....

Astonished that the new plasmas and lcd television sets provide no control to the external audio jacks, neither analog or spdif (optical), via the remote control.

Mine is a Samsung PN50C550.

I want to simply add a small powered subwoofer under the television stand. I also want to send audio to a small amplifier that is used by a member of the family that is hearing impaired.

There are quite a few options for this using the external audio jacks. Non of which will allow me to still use the tv remote for volume/mute contol. This would be bad enough, but an additional problem is that the delay sync is not balanced between the screen and the external speakers. It can be adjusted for optical output via an on screen slider from 10ms to 250ms but the analog out cannot be adjusted. If you want to use an amplifier that has neither optical input, or dedicated remote control, you are apparently just out of luck with these sets.

I could solve both of these hurdles, lip sync with the screen since internal speakers and screen are already synced by the manufacturer, and volume control via the remote, with a simple tap on the internal speakers to a dual male rca pigtail out of the back of the set . The amp that feeds these speakers may not be powerful enough to feed external speakers. But the powered subwoofer inputs as well as the little amp I'm using for powering headsets for hearing impaired are signal level inputs anyway.

The television's just beyond warranty, so I'm not worried about removing/replacing eight panel screws in the back to expose the internal speaker's terminals.

What do I put inline with the speaker tap and the signal level inputs of the subwoofer in order to...
....match the level expected by the subwoofer and aux input rca jacks on the small radio shack amplifier?
....and be quite confident that I'm not overdriving the audio amplifier within the television set?

Thanks so much for any advice.

 

[Nigel Goodwin]

Astonished that the new plasmas and lcd television sets provide no control to the external audio jacks, neither analog or spdif (optical), via the remote control.

Not at all, you don't want controlled low level outputs - you want a fixed one, FAR more useful.

But all you need is a resistor (or two as an attenuator) off the speaker connection. Try a 47K single resistor, that should be fine.

 

[wsemajb]

Not at all, you don't want controlled low level outputs - you want a fixed one, FAR more useful.

I've asked others to explain this to me. Nobody has yet. Why is it the case? What limitations or problems would controlling the level of these outputs introduce?

The analog output is not low level, but speaker, or at least headphone, level. Still not controlled via remote.

But all you need is a resistor (or two as an attenuator) off the speaker connection. Try a 47K single resistor, that should be fine.

Can I do so with reasonable confidence that, barring any miswiring on my part, doing so will not damage the television's audio amplification? As you can see, I'm limited in my understanding of electronics although I suspect that 47K is a miniscule addition of load to the amplifier. I just want to be somewhat certain.

Thank you very much for your input.

 

[audioguru]

I recently bought a 2.1 powered speaker system. The satellite speakers are much better than the crappy speakers in a TV and the sub-woofer is powerful. I connect it to the audio outputs of my digital cable TV box which has a remote volume control. The digital cable TV even has many FM radio stations.

 

[Nigel Goodwin]

I've asked others to explain this to me. Nobody has yet. Why is it the case? What limitations or problems would controlling the level of these outputs introduce?

You feed the fixed line level output to your external amplifier, the volume control is done there - you don't have a volume control on your CD Player, you don't have one on your record deck, you don't have one one your tuner , or your cassette deck - the list goes on

The analog output is not low level, but speaker, or at least headphone, level. Still not controlled via remote.



Can I do so with reasonable confidence that, barring any miswiring on my part, doing so will not damage the television's audio amplification? As you can see, I'm limited in my understanding of electronics although I suspect that 47K is a miniscule addition of load to the amplifier. I just want to be somewhat certain.

Less then miniscule, unless you connect something wrongly (on the speaker side of the resistor) you can't damage anything.

 

[wsemajb]

Thank you. Really appreciate the input. I believe what I'll do is take the back off the set and disconnect the analog audio out leads from the 1/8 inch (3.5mm) stereo headphone jack. Then reconnect that jack direct to the internal speakers with a 47k resistor inline with each (Pos or Neg? does it make a difference?) channel. I'll test run it to see if it meets expectations and then replace the chassis back cover.

I recently bought a 2.1 powered speaker system. The satellite speakers are much better than the crappy speakers in a TV and the sub-woofer is powerful. I connect it to the audio outputs of my digital cable TV box which has a remote volume control. The digital cable TV even has many FM radio stations.

Have you noticed any lip syncing issues at all? And I mean the grossest form of them, exceeding 150ms or so. I realize lip sync is an issue that the industry is struggling with at this time with so many different processing schemes sharing the same space, but these are generally much smaller timing issues and only the most demanding purists will purchase such equipment as is necessary to correct these problems "on the fly" (RE http://www.felston.com).

What I'm trying to deal with, and you might be as well if you have not checked it out carefully, are sync issues between the screen and the television's external audio jacks. These are such well known and common issues that most modern AV receivers have sound sync adjustments via the remote control. My samsung television has such adjustment, as I noted, for the optical output, but not for the analog output.

 

[wsemajb]

From another forum on this topic...

The possible problem with a speaker pickoff is that the speakers may be powered by a bridge circuit and thus not connected to a common ground. For this reason if you want to connect to the speakers I would recommend using small interconnect type audio transformers such as this...
**broken link removed**
... for isolation. You can experiment with the connections, using only one side of the center-tap or reversing the input and output to get the proper voltage level out.

Just when I was thinking I may not be out of my depth here
Any clarification on this?

 

[wsemajb]

Is there really no good consensus on something as elementary as this on an electronics board? I would think that a "speaker pickoff", or "tap" as I referred to it, whether of common ground or bridge circuit would be pretty basic electronics 101 to many of the contributors here. Am I wrong?

Is it possible to confirm whether I'm dealing with common ground or bridge circuit with a simple multimeter? Or is Common always going to show zero ohms regardless of whether it's a bridge circuit?

And could you clarify this for the sake of application? If it's a bridge circuit I'd still need the pair of 47K (approx) resistors in addition to the isolation transformers, correct?

 

[Nigel Goodwin]

Is there really no good consensus on something as elementary as this on an electronics board? I would think that a "speaker pickoff", or "tap" as I referred to it, whether of common ground or bridge circuit would be pretty basic electronics 101 to many of the contributors here. Am I wrong?

Is it possible to confirm whether I'm dealing with common ground or bridge circuit with a simple multimeter? Or is Common always going to show zero ohms regardless of whether it's a bridge circuit?

And could you clarify this for the sake of application? If it's a bridge circuit I'd still need the pair of 47K (approx) resistors in addition to the isolation transformers, correct?

You don't need isolation transformers (that was a pretty ludicrous suggestion ), just a single 47K resistor (per channel) connected to the live speaker output (or one of them if bridged), with the ground connection from chassis. It makes no difference bridged or not.

 

[wsemajb]

Thank you for that. This suggestion, from a third forum I posted this question on, seems to confirm that, and adds one more consideration.....

Even if it's bridged, you could just put a 600 ohm resistor in each leg and not worry about it. Worst case the ground of your preamp will be 600 ohm from the low bridge leg. Not going to hurt anything.

You do want to check for DC, tho. If there is DC between the speaker lines and ground, you'll need a DC blocking cap. It's important to check. I did a mod like this on my circa 2001 JVC CRT TV. Worked like a charm. No cap needed in that case.

Anyway... Given that addendum... any little addit clarification on this aspect of it? What size cap? Where it goes exactly?

Can I infer from this that pretty much anything in the range of 600 to 47K resistance is reasonable for this task?

 

[Nigel Goodwin]

Thank you for that. This suggestion, from a third forum I posted this question on, seems to confirm that, and adds one more consideration.....



Anyway... Given that addendum... any little addit clarification on this aspect of it? What size cap? Where it goes exactly?

Can I infer from this that pretty much anything in the range of 600 to 47K resistance is reasonable for this task?

You don't need a cap - a 47K resistor is perfectly fine - 600 is far too low, unless you're using it as part of an attenuator, and even then there's no reason to use such a low value.

 

[wsemajb]

Last question.... promise.....

... but the resistor goes on the pos or neg lead?

I just thought it might be important on the odd chance that the negative leads from the television's amplifer do not share a common ground.
Wouldn't directly wiring these to the common ground within on the aux inputs of an amplifier (when eventually plugged in) create a loop?

 

[Nigel Goodwin]

Last question.... promise.....

... but the resistor goes on the pos or neg lead?

I just thought it might be important on the odd chance that the negative leads from the television's amplifer do not share a common ground.
Wouldn't directly wiring these to the common ground within on the aux inputs of an amplifier (when eventually plugged in) create a loop?

It really depends if the +ve of the speaker is wired to the amplifier or ground, generally it would be to the amp, but it's not guaranteed. So connect the 47K to the +ve, and the 'ground' connection for the output to the chassis (NOT the -ve of the speaker).