Splitting line level input - AVS Forum
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post #1 of 18 Old 01-30-2013, 11:23 AM - Thread Starter
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Hoping not to offend anyone's sensibilities here, but...

I have several (currently 4, soon to be 6) zones of audio in the house (speakers installed during build - local volume controls in-line - wiring home run to equip closet). I am running these with 3 Pyle PCA1 amps (15x2 watts) fed from a Verizon Fios STB. The amps have hard power switches, so the control is via Insteon ApplianceLinc modules. I know this setup is a little hokey, but we really only use it for background music, and it sounds suprisingly ok - and all for a very manageable budget. We always use the same source for all zones - just don't always need them all on.

I have the input split 3 ways via stacked Y-cables - so far, so good. Now that I want to add more zones, I will need to split the signal further. Keeping in mind the LOW budget I'm dealing with, how many times can I reasonably split the signal?
Can I go to 5 (or better yet 6) amps? Do I need an audio splitter/amp? Is there one out there that is not meant for "broadcast professionals" (i.e. CHEAP)? If I use a composite/audio A/V splitter/amp - will it balk with no video connected?

BTW - Pyle does not list the input impedence on the amps, but what do you expect for ~$20....

Thanks!
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post #2 of 18 Old 01-30-2013, 11:58 AM
 
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how many times can I reasonably split the signal?

Assuming a 10K input impedance driven by a 100 Ohm source, you could 'split' the signal 100 times before experienceing a 3dB loss.
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post #3 of 18 Old 01-30-2013, 12:00 PM
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For that many devices, you really should install a distribution amp. No, having no video doesn't matter for amplifiers.

CIAO!

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post #4 of 18 Old 02-01-2013, 09:14 PM
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Originally Posted by SAM64 View Post

Assuming a 10K input impedance driven by a 100 Ohm source, you could 'split' the signal 100 times before experienceing a 3dB loss.
Impedance isn't the only thing to be considered here. The STB puts out about 1volt. Splitting it in 2 to feed it into 2 devices gives each device ~1/2 volt. Another split, and each gets ~1/3 volt, and so on. It eventually gets to where there isn't enough signal to be usable to any device.

With one source split to feed several devices, each time you turn a device on or off, the amount of signal available to all other devices changes, thus affecting the loudness of all.

CIAO!

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post #5 of 18 Old 02-02-2013, 10:45 PM
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Originally Posted by egnlsn View Post

Impedance isn't the only thing to be considered here. The STB puts out about 1volt. Splitting it in 2 to feed it into 2 devices gives each device ~1/2 volt. Another split, and each gets ~1/3 volt, and so on. It eventually gets to where there isn't enough signal to be usable to any device.

With one source split to feed several devices, each time you turn a device on or off, the amount of signal available to all other devices changes, thus affecting the loudness of all.

No, SAM64 is correct. The voltage will only drop of the source impedance is compromised. Now with video exactly what you say would happen because video uses an matched impedance line . But not with line level audio driven from a low impedance source into high impedance inputs.

Still I do agree, the proper way is to use a distribution amplifier to isolate the various devices.

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post #6 of 18 Old 02-03-2013, 08:37 AM
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Originally Posted by Glimmie View Post

No, SAM64 is correct. The voltage will only drop of the source impedance is compromised. Now with video exactly what you say would happen because video uses an matched impedance line . But not with line level audio driven from a low impedance source into high impedance inputs.
If you have a fixed amount of power available, doesn't each connected device draw some of that power? In other words, if a device is being fed with 1 volt, wouldn't adding a second device draw some of that power, causing there to no longer be 1 volt available for the first device?

Or is it just negligible if there's an impedance mismatch?

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post #7 of 18 Old 02-03-2013, 10:05 AM
 
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Impedance isn't the only thing to be considered here. The STB puts out about 1volt. Splitting it in 2 to feed it into 2 devices gives each device ~1/2 volt. Another split, and each gets ~1/3 volt, and so on. It eventually gets to where there isn't enough signal to be usable to any device.

No, they're in parallel, they all see the same source voltage. This is not a difficult concept.
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With one source split to feed several devices, each time you turn a device on or off, the amount of signal available to all other devices changes, thus affecting the loudness of all.

No, the value of the termination resistors doesn't change.

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If you have a fixed amount of power available, doesn't each connected device draw some of that power? In other words, if a device is being fed with 1 volt, wouldn't adding a second device draw some of that power, causing there to no longer be 1 volt available for the first device?


You may want to review series and parallel circuits. Power is measured in Watts, not volts.
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post #8 of 18 Old 02-03-2013, 04:30 PM
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Originally Posted by egnlsn View Post

If you have a fixed amount of power available, doesn't each connected device draw some of that power? In other words, if a device is being fed with 1 volt, wouldn't adding a second device draw some of that power, causing there to no longer be 1 volt available for the first device?

Or is it just negligible if there's an impedance mismatch?

Think of it this way, does your line voltage drop to 60 volts when you plug in a second lamp? No because the source impedance of the wall outlet is several magnitudes below the impedance of one or several lamps in parallel. Now does the voltage to the lamp drop if an iron or toaster is plugged into the same outlet. Yes it does probably drop a few volts because the resistance of the wire from the breaker panel combined with the high current draw is becoming significant.

And again when you get up into video and RF frequencies you can't just "wire nut" multiple devices together for reasons that are beyond the scope of this discussion but for audio you can get away with it.

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post #9 of 18 Old 02-03-2013, 11:06 PM
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Originally Posted by SAM64 View Post

No, they're in parallel, they all see the same source voltage. This is not a difficult concept.
No, the value of the termination resistors doesn't change.
You may want to review series and parallel circuits. Power is measured in Watts, not volts.
You're absolutely right that in a parallel circuit, the voltage drop across each individual branch is equal to the source voltage. It's the current that is divided up amongst the branches. If you took a 50mA circuit and connected another similar circuit in parallel, each branch would have 25mA running through it. If a third similar circuit were added, the total current draw would be equally divided amongst the three circuits, and so on. If it were a series circuit, it would be the other way around.

I guess I've just been going by what I've heard rather than what a book says. I've had a music source connected (line level) to 2 amps side by side utilizing a Y adapter (still do). I've heard the level of 1 amp drop when I have turned on the 2nd amp. Nothing major, but a drop nonetheless.

CIAO!

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post #10 of 18 Old 02-03-2013, 11:34 PM
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Originally Posted by Glimmie View Post

Think of it this way, does your line voltage drop to 60 volts when you plug in a second lamp? No...

In parallel circuits, the voltage across each of the branch circuits is equal to the source voltage, so, of course, there's going to be the same ~120 volts across all lamps. Other than that created by the circuit breakers and wiring itself, a house circuit doesn't have much limitation of power available, so you can add 100 watt lamps to a circuit and not see any difference. If you placed that lamp in a circuit where the power source was only capable of supplying 100 watts of power, the lamp would be at full brilliance. If you added a second 100 watt lamp, the voltage across it would be the same 120 volts, but it would dim some because it would only be able to draw 50 watts. The other lamp would be drawing the other 50 watts.

CIAO!

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post #11 of 18 Old 02-04-2013, 08:18 AM
 
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I guess I've just been going by what I've heard rather than what a book says.

That's one of the problems with these fora. Too many experts who don't understand the basics.
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If you added a second 100 watt lamp, the voltage across it would be the same 120 volts, but it would dim some because it would only be able to draw 50 watts. The other lamp would be drawing the other 50 watts.

Sort of...you need to brush up on series and parallel circuis, you're still not quite getting it.
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post #12 of 18 Old 02-04-2013, 09:32 AM
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Originally Posted by SAM64 View Post

That's one of the problems with these fora. Too many experts who don't understand the basics.
Got that right. wink.gif I don't claim to be an expert, but the ears don't lie.

CIAO!

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post #13 of 18 Old 02-04-2013, 10:44 AM
 
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but the ears don't lie.

Your brains interpretation of the signal received by your ears does.
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post #14 of 18 Old 02-04-2013, 01:14 PM
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Originally Posted by egnlsn View Post

In parallel circuits, the voltage across each of the branch circuits is equal to the source voltage, so, of course, there's going to be the same ~120 volts across all lamps. Other than that created by the circuit breakers and wiring itself, a house circuit doesn't have much limitation of power available, so you can add 100 watt lamps to a circuit and not see any difference. If you placed that lamp in a circuit where the power source was only capable of supplying 100 watts of power, the lamp would be at full brilliance. If you added a second 100 watt lamp, the voltage across it would be the same 120 volts, but it would dim some because it would only be able to draw 50 watts. The other lamp would be drawing the other 50 watts.

Let's try this. How much current does it require to produce 2 volts (standard consumer audio level) across 100 ohms? You can just use ohm's law and not worry about AC issues for this example. Now how much current does it take to produce 2 volts across 10,000 ohms?

Like Sam said above it's all about POWER (V * A). As long as you have enough power, you can trade current and resistance against each other in a DC or AC circuit. With a transformer you can also trade voltage against current but only on an AC circuit. As a 10K load will consume far less current than a 100 ohm load, you can use that extra current for more 10k loads.

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post #15 of 18 Old 02-04-2013, 01:38 PM
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Originally Posted by SAM64 View Post

Your brains interpretation of the signal received by your ears does.
Don't think so, Tim...

CIAO!

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post #16 of 18 Old 02-04-2013, 02:18 PM
 
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Originally Posted by egnlsn View Post

Don't think so, Tim...

well, ignorance is bliss wink.gif
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post #17 of 18 Old 02-04-2013, 05:47 PM
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Originally Posted by egnlsn View Post

I've had a music source connected (line level) to 2 amps side by side utilizing a Y adapter (still do). I've heard the level of 1 amp drop when I have turned on the 2nd amp. Nothing major, but a drop nonetheless.

That's quite possible if the preamp or driving device had a rather high impedance and the two amps were on the lower impedance end. Of course we would need hard numbers to calculate the exact voltage drop but I don't doubt it happened.

However in the first example here we had a 100 ohm source driving several 10k ohm receivers. In this case and voltage drop is negligible.

Like I said before this has become an engineering exercise. Personally I would still use a DA to provide isolation. But you can usually get by without in this application.

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post #18 of 18 Old 02-05-2013, 07:27 AM
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Originally Posted by Glimmie View Post

That's quite possible if the preamp or driving device had a rather high impedance and the two amps were on the lower impedance end.
That could be...

CIAO!

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