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70V - Wattage on Line
This thread has 13 replies. Displaying all posts.
Post 1 made on Monday August 7, 2017 at 11:15
imt
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So, if I have a Crown Cdi1000 and Ch2 (500W) is set to 70v, is the wattage on the main speaker wire equal to what the taps are set?

For example, I have 4 sat's each tapped at 15w. Is then only 60W total power then riding on that speaker line? I ask since I need to add another TPD surge speaker line suppressor (only connected to the 70v channel) and there is the 250w model and the 1000w model. Amp puts out 500W but if taps settings restricts watt output and is below 250W I can then use the lower wattage unit. Wasn't sure in a 70V system.
Post 2 made on Monday August 7, 2017 at 11:35
lippavisual
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Amp will only provide what is being called for.

So if you have 4 spkrs @ 15W each. 60 Watts
Post 3 made on Monday August 7, 2017 at 12:37
Brad Humphrey
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The TPD you are referring to is for 4/8 ohm systems. Of special note: the clamping voltage is 100VRMS.

You need to call TPD and check if that module will work on a 70v system. The audio signal rides on that 70v line so peak voltage can be well above 100v in use.

I'm willing to bet that TPD module can NOT be used on a 70v system. When you go to crank up the system, the TPD module will shunt, sending the amp into protect mode.

But again, call and check - if it can't, they may have a part number they sell that does do what you need.
Post 4 made on Monday August 7, 2017 at 13:01
Ernie Gilman
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This is a technical question so I'll try to answer it in technical terms.
On August 7, 2017 at 11:15, imt said...
So, if I have a Crown Cdi1000 and Ch2 (500W) is set to 70v, is the wattage on the main speaker wire equal to what the taps are set?

As I think you're understanding it, yes.
However, "wattage on the wire" is a strange thing to say. The power drawn by the speakers when the amplifier is set to its full output is the same as the sum of the tap wattages of all the speakers, modified by the volume control(s) and gain structure to the actual wattage being output at the moment.

With exactly the same wiring and tap settings, when the volume is all the way down, NO wattage is drawn, so no "wattage on the main speaker wire" is present. When the output volume is, say, 10 dB below the power amp's maximum specified level (70 volts), then the power drawn by the speakers is 10 dB below their tap value. In the example you give, this would be 6 watts output.

For example, I have 4 sat's each tapped at 15w. Is then only 60W total power then riding on that speaker line?

Nothing rides on the line. If you had no speakers connected to the amp, and you turned up the amp, then a voltage could be measured on the line but no current would flow so no power would be output. Is that "riding on the line?" I don't know.

But you ask:
I have 4 sat's each tapped at 15w. Is then only 60W total power then riding on that speaker line?

If you have 4 sats, each tapped at 15w, and you turn up the inputs to the power amplifier such that its output reaches 70 volts, at that point 60 watts would be being drawn by the speakers, so yes. (We always overlook that at lower volume control settings, there's lower or even zero output.)

I ask since I need to add another TPD surge speaker line suppressor (only connected to the 70v channel)...

What tells you that you need to add another speaker line suppressor? Could the same thing be accomplished by moving the one you have, for instance to the point where the wires leave the house?

and there is the 250w model and the 1000w model.

I only see literature on one model, the 250 Watt TPD-AmpPro, at [Link: cdn-docs.av-iq.com]. Before going on about 70 volt operation, let's note that it says it is designed for
4/8 Ohm Audio Systems

This changes how we should view these details.

A 70 volt amp reaches its maximum (clean) output level when its input level makes it output 70 volts. The amount of power drawn depends on the amount of load connected to it. Yes, the sum of the taps gives you that figure.

A power amplifier designed for use with four ohm and eight ohm loads is not designed to deliver such a high voltage. It is designed instead to output a much higher amount of current. 4 and 8 ohm loads are MUCH higher loads (lower resistance*) than most 70 volt loads!

Ohm's Law formulas are given below for reference. The lower one in pink says that voltage equals the square root of the wattage times the load. From this, we get that the output of a power amplifier that's feeding 250 watts to an 8 ohm load measures 44.7 volts. A power amplifier that's feeding 100 watts to a 4 ohm load measures 31.6 volts.

This means you're hoping to use a device the manufacturer targets for use with a maximum of 31.6 or 44.7 volts. You're going to use it with 70 volts.

Now, the sheet also says that the Maximum Operating Voltage is 100V RMS, which is more than twice the 44.7 volts of 250 watts into 8 Ohms. With a 70 volt amp, this is a lower safety margin than they design for, but it might be okay.

Amp puts out 500W but if taps settings restricts watt output and is below 250W I can then use the lower wattage unit. Wasn't sure in a 70V system.

The amp puts out 70 volts (I hate to keep repeating, but it puts out 70 volts only when it's at full power). The 250 Watt unit lists a maximum operating voltage that is 100/44.7 times the higher voltage that it's specced to work at. If you used the unit with 1000 watt rating, that should increase your safety margin enough. I only found the data sheet on the lower power unit, so I can't come up with any actual numbers on this.

You should call the manufacturer and ask about these things.









*yeah, yeah, I know, impedance.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 5 made on Monday August 7, 2017 at 13:05
Ernie Gilman
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Written while I was writing:
On August 7, 2017 at 12:37, Brad Humphrey said...
The TPD you are referring to is for 4/8 ohm systems. Of special note: the clamping voltage is 100VRMS.

You need to call TPD and check if that module will work on a 70v system. The audio signal rides on that 70v line so peak voltage can be well above 100v in use.

If you're going to speak of RMS, you have to speak only of RMS; the same goes for peak. The peak of a sine wave is 1.414 times its RMS value.

The peak voltage of a 70V sine wave is 98.98. The peak voltage of 100V RMS is 141.4 volts. This says that a 70V system should not cause the TPD to activate. SHOULD is not a good engineering term, though!

I'm willing to bet that TPD module can NOT be used on a 70v system. When you go to crank up the system, the TPD module will shunt, sending the amp into protect mode.

But again, call and check - if it can't, they may have a part number they sell that does do what you need.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 6 made on Monday August 7, 2017 at 13:21
buzz
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Resources: [Link: juicegoose.com], [Link: l-com.com]
OP | Post 7 made on Monday August 7, 2017 at 15:52
imt
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Thanks. Ernie.

I was going to reply earlier that I read that 70V systems are really 70.7 rms since they are based on peak voltage of 100v.

I was corresponding with TPD and 70V systems are fine with te AmpPro. The 100V RMS is somewhat padded and is really a little higher. The 100V is also per channel. They are working on an updated datasheet.

The reason for the initial post is that the TPD screw down terminals are limited to 12ga wire and I needed to use doubled up 12ga. I would then have to use 1 entire AmpPro-1000 for just the Sub on and the 4 wires. I then would need to get another AmpPro for just the 70V Sat's and figured I could then use the lower cost model AmpPro-250 if I was only running 4 speakers (highest Watts at 30W setting anyway is 120 watts).

For a shorter run to the Sub, I would then have been able to use 1ea AmpPro-1000 for both the 70V ch and 8ohm ch.



vs on a shorter run of just 1ea 12/2 using the AmpPro-1200 for both the 8ohm sub and the 70V sat's.

I would need 1 AmpPro for just the 70V and if the wattage was under 250W I thn could use the lower cost AmpPro-250.
Post 8 made on Monday August 7, 2017 at 17:11
Ernie Gilman
Yes, That Ernie!
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If you have to use conductors larger than a device's screw terminals will allow, get some barrier strips and double up there.


The following image doesn't show what you'd use, but it shows how you'd mechanically do it.

A certain size wire at the left goes to your device.
There are shorting bars or shorting pieces of wire from one screw to the next screw on each strip. This gives you multiple screws you can connect your other wires to, allowing doubling up.

FYI it's easier to do this with this kind of strip than with the euro strips because the euro strips are harder to daisy-chain.

A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
OP | Post 9 made on Monday August 7, 2017 at 21:27
imt
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My wayward thinking was that going from doubled up 12ga to a short single piece of single 12ga through the surge protector would be restricting.

I could use something like a Wago connector tying the 3ea 12ga (2x to amp and 1x to surge) then repeat on other side of AmpPro.
Post 10 made on Monday August 7, 2017 at 23:27
Brad Humphrey
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On August 7, 2017 at 21:27, imt said...
My wayward thinking was that going from doubled up 12ga to a short single piece of single 12ga through the surge protector would be restricting.

I could use something like a Wago connector tying the 3ea 12ga (2x to amp and 1x to surge) then repeat on other side of AmpPro.

How large of a gauge wire is in a fuse? How much wattage do you see going thru that?
Resistance is a measure of square area and distance. You could use 18awg wire if your jumper is only 6 inches long. It isn't going to matter.
Better yet, open up that crown amp real quick and look at the gauge wire used for the internal speaker wire. Bet it is 20awg or 18awg at most. Again, a short jumper does NOT have a lot of resistance, even at small gauges. It's the longer runs that matter.

By the way, are you using the 12awg on the 70V lines? You know that is super overkill right. One of the points of a 70V system, is the ability to use MUCH skinnier gauge wire. You can use 16awg for 200watts, up to 350 feet (according to some charts). Or 16awg for 400watts, up to 175 feet.
OP | Post 11 made on Tuesday August 8, 2017 at 00:16
imt
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On August 7, 2017 at 23:27, Brad Humphrey said...
How large of a gauge wire is in a fuse? How much wattage do you see going thru that?
Resistance is a measure of square area and distance. You could use 18awg wire if your jumper is only 6 inches long. It isn't going to matter.
Better yet, open up that crown amp real quick and look at the gauge wire used for the internal speaker wire. Bet it is 20awg or 18awg at most. Again, a short jumper does NOT have a lot of resistance, even at small gauges. It's the longer runs that matter.

By the way, are you using the 12awg on the 70V lines? You know that is super overkill right. One of the points of a 70V system, is the ability to use MUCH skinnier gauge wire. You can use 16awg for 200watts, up to 350 feet (according to some charts). Or 16awg for 400watts, up to 175 feet.

the 2x12ga is just for the subs.

70v will be 16ga. Max for 8 speakers would be 240 watts. But I also thought I saw in the charts that you could go closer to 230' at 400 watts.
Post 12 made on Tuesday August 8, 2017 at 01:33
Brad Humphrey
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It depends on how much loss is acceptable and who's chart you are looking at. That's why I mentioned "according to some charts".
For just PA use, you will see charts from Bogen and such, with very long distances listed for power.
Harman and others are going to be a lot more conservative on the side of fidelity.
Post 13 made on Tuesday August 8, 2017 at 04:10
buzz
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One could use Ernie's terminal block scheme or any other mechanical contraption that you can think of to make a wire size reduction. Really, you are simply adding a small additional series resistance that is not very significant compared the run of a couple hundred feet of wire. The limit, of course, is if the reduced section melts or causes a fire due to the current.

If you are majorly concerned about this, don't ever insert a fuse in speaker circuit.

I don't know about the present product line, the original Haffler power ampliers placed the speaker fuse inside the feedback loop in an an effort to minimize audible consequences. This would result in some unusual symptoms when the fuse blew because there was still a small amount of very distorted output -- making one believe that the amplifier was "blown". I would use this to my advantage in the store when dealing with a jerk. I had a 6th sense that one of these jerks would seize the Volume control and turn it up past "11". I kept the Haffler speaker fuse a little under size and used it for these demos. After a few seconds at "12" the fuse would blow, the amplifier would sound blown, and the jerk would leave. This was a lot quicker and easier than my throwing a fit and tossing them out. Further, it had the advantage that the jerk would tell his (they were always male) jerk friends about the wimpy equipment that I carried and they'd stay away too.
Post 14 made on Tuesday August 8, 2017 at 12:17
Ernie Gilman
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On August 7, 2017 at 21:27, imt said...
My wayward thinking was that going from doubled up 12ga to a short single piece of single 12ga through the surge protector would be restricting.

The important thing to remember is that a piece of 12 ga wire has twice the resistance of an equal length of doubled-up 12 ga wire (assuming [big assumption sometimes] that the connections are essentially zero ohms).

Let's say you crimp or solder two 12 ga wires together and add a six inch tail of 12 ga wire.

The resistance that tail would add to your wire run would be the same as one foot of doubled-up 12 ga wire. Are you freaking out about how many feet long the wire run is? To the point where one foot of wire length is a big deal?

Next, this point of view: 12 ga wire has a resistance* of 1.588 ohms per thousand feet, that six inches of 12 ga wire would add 0.794 MILLIohms to your wire run.

I could use something like a Wago connector tying the 3ea 12ga (2x to amp and 1x to surge) then repeat on other side of AmpPro.

A Wago connector, or any other connector that just slides or snaps together, would probably add more resistance than that six-inch wire tail.



*Find a chart of wire sizes and resistance and put it in your "Tech Info"** computer directory so you can easily look up actual numbers when you're debating what to do.


**Really -- each of us should have a section of files like this. CATV channel frequencies. Bolt sizes. Bolt strength. Electronic formulas. all kind of stuff.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw


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