Question on bi-amping - Page 16 - AVS Forum
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Old 11-20-2013, 09:50 AM
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Originally Posted by amirm View Post

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Originally Posted by arnyk View Post

Wrong. All of the pictures I showed had exactly one power transformer, and that says no split at the point of the weakest link in the power supply which is the power transformer.

It is pretty easy to show that the transformer is not the weakest link in our scenario.

Let's assume we have a stereo amplifier that we measure to put out 100 watts for each channel. The total power output is 100+100 = 200 watts. Assuming the amplifier is 50% efficient to make the numbers easy, the power supply would need to pump 2*200 = 400 watts of power into the amplifier or else, we cannot have 100/Channel rating. And that transformer better be able to support this level of output.

The statement "And that transformer better be able to support this level of output." is a supposition without any relevant support in sight.

The calculations are moot because my point was that with only one power transformer, how the power is split among multiple power transformers is obviously moot.

In short, I don't know what you are talking about, Amir.
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Old 11-20-2013, 10:33 AM
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Quote:
Originally Posted by arnyk View Post

The statement "And that transformer better be able to support this level of output." is a supposition without any relevant support in sight.

The calculations are moot because my point was that with only one power transformer, how the power is split among multiple power transformers is obviously moot.

In short, I don't know what you are talking about, Amir.
I will be more explicit about the punch line. We know that if we had two fully separate power supply for each channel in passive bi-amp, the tweeter amp will enjoy higher voltage.

Now, let's plug both power supplies into the identical 15 amp outlet. 15 amp outlet (assuming ideal power factor) will give us 15 * 120 = 1,800 watts in US 120 volt land. Would you say that sharing an outlet will cause the output of the two power supplies to be the same? I assume not. At maximum power we only need 400 watts so clearly the single outlet will not be bottleneck and cause the output of the two power supplies to telegraph each other.

The next step in integration is to use a common transformer for both power supplies. As I explained, the common transformer is fully capable of putting out 400 watts. In our scenario we only need 220 watts. Just as the analogy of a shared outlet, we can conclude that while there may be some crosstalk between the two power supplies, it will not be sufficient to force the output of one supply to be the same as the other. Here is a picture of this scenario:

p04_fig1.gif

We now have dual banks for the positive rail at 35 volts and dual banks for the negative rails at -35 volts with a shared transformer. What predominantly determines the dynamic voltage from each pair from the other pair is the element that deals with dynamic power: the capacitor bank. Since we have two separate banks in this situation, we can count on the two supplies to remain "decoupled." That is, changing the output of one will not force the other to rack it as would be the case if we have a single power supply from start to finish and the connection for both amps is to the same point.

Hope this is clear now. If it is not perhaps I can ask for help from other electrical engineers in the crowd to try to explain it smile.gif.

Amir
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Old 11-20-2013, 01:15 PM
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Quote:
Originally Posted by amirm View Post

It is pretty easy to show that the transformer is not the weakest link in our scenario.

Let's assume we have a stereo amplifier that we measure to put out 100 watts for each channel. The total power output is 100+100 = 200 watts. Assuming the amplifier is 50% efficient to make the numbers easy, the power supply would need to pump 2*200 = 400 watts of power into the amplifier or else, we cannot have 100/Channel rating. And that transformer better be able to support this level of output.

Now let's look at our passive bi-amp situation. We take the channel that is feeding the woofer and "dial it past 12" to 105 watts. It is now distorting the signal. We take the other channel and drive the tweeter with it (both through crossovers of course). As we all agree I think, the amp driving the tweeter will be barely working. Let's say it is outputting 5 watts. Adding the power output for both amps we get 105+5 = 110 watts. Multiplying by two to incorporate the amplifier efficiency we get 2*110 = 220 watts.

220 watts is much less than 400 watts. Since the power supply transformer was designed to drive 400 watts, it clearly is not a barrier to achieving 220 watts.

So our problem here is not the transformer at all. The problem is that each channel of the amp is using wildly different amount of current from an unregulated power supply. And that causes the voltage as seen to by the amplifier from the power supply to differ. The tweeter amp will enjoy higher voltage and therefore, higher threshold of clipping as opposed to woofer amp. Thereby we gain something from passive biamping even in the voltage argument.

We understand what you are saying - if the tweeter isn't being driven by the same amp as the woofer, then the voltage sag on the power supply for the woofer's amp (assuming this even occurs at volumes that don't cause your ears to bleed) won't affect the maximum voltage attainable by the tweeter amp and should allow it's output to be cleaner. But to get this scenario, you need ANOTHER amp with the same gain and voltage rail just to drive the tweeter, otherwise its maximum voltage will NOT be the same.

My question is, instead of buying two amps with the same gain and rail voltage why not just buy one more powerful stereo amp with a rail voltage that is significantly higher? Even if driving the woofer to the same level causes the voltage to sag (I still don't believe this is an issue even at reference levels and any reasonable impedance), it will still be a higher voltage than the smaller amps and now there won't be any negative affects on either the woofer (because it can sound bad as well) OR the tweeter.

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Old 11-20-2013, 01:44 PM
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Originally Posted by kiwi2 View Post

If you are an electrical engineer then I am surprised you used such a poor analogy.

The moment someone sticks their keys into an electrical outlet (that didn't have anything plugged into it obviously) they create an earth and thus a path for current to flow. You can have all the voltage you like sitting in your lines but with nothing plugged into any of the sockets they will be practically inert. The wires will not get hot, fuses won't blow, and the metre board won't measure any power and you will get a $0 power bill at the end of the month.

It's why birds can sit on 24k volt power lines and for all intents and purposes that voltage is irrelevant to them... but if they were to touch an earth while sitting on that 24k volt line and current begins to flow... it all of a sudden becomes relevant to them.

Voltage without a path means very little from an electrical standpoint.

Even I knew that analogy was wrong based on grade 2 science class!
Anyway, I'm curious to read the debate among those of you (with credibility) tackle the latest supporter for biamping, who are basically saying what I was trying (but utterly failed smile.gif to say. It's all about current, distortion, etc... not necessarily about voltage and clipping.
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Old 11-20-2013, 01:48 PM
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Originally Posted by arnyk View Post

You get to be wrong! ;-)

Sorry, your credibility is shot, over and over.
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Old 11-20-2013, 01:53 PM
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Originally Posted by chashint View Post

I love this thread.
Keep up the good work Arnold, you are much more dedicated to education than I am.
When laymen apply a child's logic to what they believe is magic it frustrates me after only a couple of circles, no matter what you tell them they will not even attempt to understand.

ummm did you hear what he said about sticking your fingers in an electrical socket?
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Old 11-20-2013, 01:54 PM
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Originally Posted by arnyk View Post

In short, I don't know what you are talking about, Amir.

Indeed!
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Old 11-20-2013, 02:06 PM
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Originally Posted by DonH50 View Post

@stereoforsale: There's no point in continuing this debate. Others are doing fine. My background and experience says one thing and yours says another, I'll leave it at that.

Don, you seem to be one of the open minding anti-passive-bi-amp person here with any real credibility. The "others" you speak of don't seem to have grasp on EE as you do (sorry arnyk... you lost us at "hello"). What's your final say on the views of Amir, Mark and Theatredaz?
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Old 11-20-2013, 02:42 PM
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Originally Posted by stereoforsale View Post

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Originally Posted by DonH50 View Post

@stereoforsale: There's no point in continuing this debate. Others are doing fine. My background and experience says one thing and yours says another, I'll leave it at that.

Don, you seem to be one of the open minding anti-passive-bi-amp person here with any real credibility.

Common strategy for creating dissension in your opponent's group:

Pick out one person in an otherwise indivisible group and tell him that he is your hero.

For extra points publicly announce that the others are bozos.
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The "others" you speak of don't seem to have grasp on EE as you do

Second strategy for creating dissension in your opponent's group:

Pick out the biggest threat and try to neutralize him with a vague complaint:
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(sorry arnyk... you lost us at "hello").

Trust me kid, the best strategy in a debate is to be tasked with supporting the truth.

So much for a kinder and gentler AVS... ;-)
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Old 11-20-2013, 02:48 PM
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Nice try. You dug your own grave: "Look at it this way - if you stuck your keys into an regular electrical outlet that was on a live circuit but had nothing plugged into it so no current was flowing, what would happen?"

I won't bother getting into the hypocrisy of your statements above. What you are doing is called "projecting". Please stop, you've embarrassed yourself enough already.

You so desperately want the "world to be flat" that you are willing to twist grade 2 science to make your point. It's called manipulation, denial, and bad science. Nothing vague about it - you have zero credibility kid. Moreover, you (yes YOU) mock and insult others. I don't recall anyone else resorting to those childish tactics. Take your own advice and be respectful of others on the forum.

In any event, if I insulted you (unprovoked), then I sincerely apologize... I may be a bit cheeky, but it's only meant to add some levity to this deathly serious subject of passive biamping smile.gif
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Old 11-20-2013, 03:49 PM
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Hey diomania, I have just taken a frequency response measurements of my room 10 minutes ago just for you...

Here it is at 1/6 octave...



And at 1/24 octave...



(click on pic then click on 'original')

Now lets see your room as it is at the moment...???
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Old 11-20-2013, 04:24 PM
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* I also feel you have to have a real set of amazing tweeters to consider bi-amping. Ones that stand out on their own without bi-amping.
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Old 11-20-2013, 04:32 PM
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Originally Posted by theatredaz View Post

* I also feel you have to have a real set of amazing tweeters to consider bi-amping. Ones that stand out on their own without bi-amping.

Would 30" tall ribbons count..?? smile.gif
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Old 11-20-2013, 05:47 PM
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The moment someone sticks their keys into an electrical outlet (that didn't have anything plugged into it obviously) they create an earth and thus a path for current to flow.

They only create "to earth" loop if they standing on a floor that has connection to house ground. If you are on a tile, vinyl or wood floor that is isolated from panel ground (either ground rod or ground plate - where do you figure current flow would happen to? Please explain.
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Old 11-20-2013, 06:59 PM
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Originally Posted by arnyk View Post

It doesn't stay exactly the same because amplifier efficiency varies with output. However, estimating that it remains the same is a good first estimate.

This is a plot of the efficiency of a typical 150 class AB power amp versus output:



The amp's efficiency is 65% from the chart at 150 watts output, which means that it draws about 230 watts from its power supply when supplying 150 watts to the speakers.

If we split the 150 watts up equally among two amps, their efficiency from the chart at 75 watts output each drops dramatically to 45%, so each amp draws 166.7 watts for 333.3 watts total. 333 watts > 230 watts and not by just a little bit!

In this case if the passive biamping splits the power equally between the two amps, it would put greater stress on its power supply and is possible it may even somewhat decrease the actual maximum power available, total. This is because passive biamping tend to significantly decrease the efficiency of the power amp. Class AB power amps are most efficient near full output and passive biamping reduces power output per channel.

The efficiency explanation makes complete sense. Maybe important if power demands are high enough. The more compelling point for me is that you mentioned splitting power when biamping.

I assumed that each amp supplies equal wattage in a passive config and the speaker's high and low frequency filters discard the undesirable frequencies and power.

Example: given two frequencies and speaker impedance 8ohm for each, high freq requiring 25w and low freq 75w, a total of 100 wpc to both left and right channels. Each of the four amps supply 100 watts, 400 watts total, and the speaker crossover/driver then discards the unneeded 25w/75w.

Is that incorrect?
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Old 11-20-2013, 07:26 PM
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Originally Posted by kraut View Post

They only create "to earth" loop if they standing on a floor that has connection to house ground. If you are on a tile, vinyl or wood floor that is isolated from house ground (either ground rod or ground plate - where do you figure current flow would happen to?

I don't know. You should try and find out for us.
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Old 11-20-2013, 07:29 PM
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Originally Posted by whoaru99 View Post

My reason is that just becase an amp has to swing voltage doesn't mean it's a big burden on the power supply. I can crank the output of an amp to clipping, but with no load it doesn't draw much power. The crossover HPF/LPF presents higher impedance to out of band signal thus while voltage still swings full range, high impedance out of band means less current, thus less power.

Are you assuming that speaker impedance is lower for the high frequencies?
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That said, Arny has provided an interesting aspect for consideration. I detect an experiment in my future, although it will be at least a week since a business trip is imminent, as in plane leaving 3pm today and I have to leave about 4 hours before then.

Experiment? Hope you remembered to send your lab coat out for a proper cleaning before leaving.
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Old 11-20-2013, 07:41 PM
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Originally Posted by amirm View Post

False in almost every case? What is your market sample size for that Arny? Here is the amplifier that powers part of my theater, the Proceed Amp-5 which as the name indicates has 5 channels:

index.php?action=dlattach;topic=129858.0;attach=121045;image

They even have numbers for each power supply! See how each has a toroidal transformer in front, and capacitor pairs for each?.

Sheesh! Does the Proceed manual specify a dedicated nuclear plant for the home outlet?
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Old 11-20-2013, 07:43 PM
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Hey, you are the one who stated that just because I insert a conducting object into an outlet that current will flow, even without connection to ground or neutral. Your answer shows that your notions of electrical theory is less than 0. Without a connection to a lower potential i.w. neutral or ground no current will be flowing.

If you make statements, don't ask me to defend them for you. Either answer or admit that you haven't got the foggiest.

Maybe electrical theory is different in NZ?
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Old 11-20-2013, 08:05 PM
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So have you stood on your kitchen vinyl floor and stuck a fork in a power socket yet...???
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Old 11-20-2013, 08:32 PM
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Originally Posted by kiwi2 View Post

So have you stood on your kitchen vinyl floor and stuck a fork in a power socket yet...???

A trick question to be sure. Is this an 8ohm or 4ohm fork and what kind of crossover? Was the floor wet from a recent mopping? Would the results be different if one were lying down and used a spoon?
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Old 11-20-2013, 08:39 PM
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There is no spoon!

It would be silly (if you want to stick fingers in power outlets) to assume that objects that are considered to be poor choices of earth, have no earth.

Regardless of the end results, the analogy was still a very poor choice by arnyk.
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Old 11-20-2013, 08:42 PM
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Or let's hope the polish used on the kitchen floor didn't have conductive properties to it.
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Old 11-20-2013, 08:54 PM
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Originally Posted by kiwi2 View Post

Or let's hope the polish used on the kitchen floor didn't have conductive properties to it.

Because Audiophiles would be coating their speaker wires with it and describing the layers of sound that were revealed.
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Old 11-20-2013, 08:58 PM
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Originally Posted by kiwi2 View Post

Or let's hope the polish used on the kitchen floor didn't have conductive properties to it.

Actually this makes a good point about resistance downstream. A small amount of conductivity (say from the polish on the vinyl floor) could result in a tingling sensation from touching high voltage. A more conductive floor surface could result in a fatal shock from the same voltage source.

Resistance/a path downstream dictates current flow upstream.
..
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Old 11-20-2013, 09:44 PM
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Good grief this has degenerated!

I used to work as an electrician and often handled live wires. How much of a shock is felt is dependent upon many variables. A better analogy might be to think of a battery. If you do not load it, the voltage (potential) is still there. Apply a load, and due to internal resistance and cell capacity the voltage will drop a little, increasing to a lot as the load becomes large (i.e. a smaller resistor).

I read Amir's post a couple of times but am practicing and chasing some work stuff so just didn't quite grasp it. I will just note that IME (that is important!) the transformer may be the limiting factor for many AVRs because not all channels are required to provide full power all the time. Big transformers cost a lot and take up a lot of space. For many amplifiers the limitation is the decoupling (filter) capacitors as they cannot support the charge needed for continuous large signals and allow the rails to sag. Even with separate (distributed) capacitors, if the rails sag in one channel, with a single supply that will begin to draw from the others and the entire rail sags. The output transistors drop more voltage as current increases, another source of reduced output voltage, and this parameter is independent of the other channels (to first order). Etc. There are so many variables from amp to amp and system to system, and so many different components out there, that I find speaking in other than general terms can be dangerous Somebody can always find a counter example, be it the behemoth amp that doubles down to 2 ohms or the speaker that exhibits below 1-ohm impedance over most of its bandwidth.

My belief is that for the vast majority passive bi-amping is a waste of effort with negligible audible benefits. The theoretical pros and cons are pretty clear, but there will always be those who claim to hear benefits present or not (expectation bias, and in some case actual differences such as changes in level and such produce a perceived benefit that is not fundamentally due to passive bi-amping but a different change in the system). While Amir makes some good points, I tend to lean with Arny in that in the real world and at usual volumes with typical speakers current limiting is less an issue than voltage clipping, usually due to flat-out asking an amp to deliver more voltage (and thus power) than it can provide. I tend to post during breaks and so have not really kept up with all the opinions; Arny and Amir are both known to me (and me to them), at least in a 'net kind of way, and I respect them both. That said, IME, which includes simulations, a few measurements, and only a couple of trials, I have observed no benefit with passive bi-amping.

I am not into picking winners and losers. Each of us has presented our case with varying clarity and passion, and it is up to the reader to decide. Sometimes the only answer you will ever get is "because I believe/hear it". As an engineer and audiophile I tend to do my own research when something is not clear, either reading a text or refereed journal, measuring and listening tests, or both. As a musician I keep reminding myself that ultimately I am listening to the music, not the gear, and should find better things to do than argue on an audio forum where I am unlikely to convince either side they are right or wrong. Or someplace in the middle. On the net it can be very hard to determine a poster's credibility. Some here have found my profile on Linked In and so forth so at least know some of my background and experience (though none of my audio experience is there, not really relevant to my primary career), other names are well-known in the industry. But there are extremely talented, intelligent, knowledgeable folk that most would not know, names they would not recognize, and grade-schoolers with a PC who can present themselves as Einstein. Can be tough to sort out...

In the meantime, I need to get back to practice. Why every cantata arranger feels they must tweak the key and rhythm of the classics I'll never know, but at least there's lots of fun stuff different from my usual orchestra and big band gigs...

FWIWFM, IMO, my 0.000001 cents (microcent), etc. - Don
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Old 11-20-2013, 11:50 PM
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So have you stood on your kitchen vinyl floor and stuck a fork in a power socket yet...???

I ask a question and get ******** for answer? Shows maturity for sure. Or rather manurity.
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Old 11-21-2013, 12:05 AM
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Wasn't your "question" already answered in the very same post you quoted from..?

"It's why birds can sit on 24k volt power lines and for all intents and purposes that voltage is irrelevant to them... but if they were to touch an earth while sitting on that 24k volt line and current begins to flow... it all of a sudden becomes relevant to them."

Unless there is a path for current to flow, no current will be drawn.
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Old 11-21-2013, 07:07 AM
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Originally Posted by kiwi2 View Post

Wasn't your "question" already answered in the very same post you quoted from..?

"It's why birds can sit on 24k volt power lines and for all intents and purposes that voltage is irrelevant to them... but if they were to touch an earth while sitting on that 24k volt line and current begins to flow... it all of a sudden becomes relevant to them."

Unless there is a path for current to flow, no current will be drawn.

But here's an important point: Even though no current may be flowing, the generators in the power station are still grinding out the voltage, the transformers along the way are stepping it up and down, and its right there on the power line to do its magic on anything that completes the circuit.
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Old 11-21-2013, 10:19 AM
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Location: New Zealand
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But it is easy for a generator to create just voltage by its self. The work/load comes when it needs to put out amps.

There is little resistance to the coil in the magnetic field when it is spinning and creating the voltage. But the moment you start to draw a current, say from a light bulb, then you put a load on trying to turn the coil.
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