As some of you know I have converted a McMartin PA to a guitar amp(thanks for your help). I saw somewhere that on a Bogen PA amp you may run a 4 Ohm speaker from common to the 25V tap? Is this the case? I have a 4 Ohm speaker made in england I would like to use. My amp only has 8 Ohm, 70V and 25V taps. Can I do this as stated above or is there another way? Thanks.
A 4ohm speaker on 25volt tap,ykes!
You must first understand the commercial sound systems. A 25volt line is as follows: 25vX25v= 625ohms this is how the 25volt speaker line is figured. Hince a 4 ohm load into a 625 ohm would equal a load on the amp of 156watts. Your 4ohm speaker when hooked up to the 25volt leg without ANY transformer would pose a 156.25 watt load on the amp. By the same token a load on the 70 volt side is figured as 70.7vX70.7v=4998ohms. The value of both 25volt and 70volt lines are to drive quantities of speakers and a heck of a lot of wire without problems. a 25volt line would drive a maximum of 625 speakers tapped at 1watt on the 25volt transformer. Do the math and you can see the value of the commercial speaker system as opposed to trying to series parallel 8 ohm speakers.
To answer your question...NO, do not use a 4 ohm speaker on the 25volt tap or the 70volt tap either. You would be better to put it on the 8ohm tap as opposed to anything else. Better yet use an 8ohm speaker.
Tube amps are more forgiving than any SS amp would ever be when it comes to overloading.
Joe
You must first understand the commercial sound systems. A 25volt line is as follows: 25vX25v= 625ohms this is how the 25volt speaker line is figured. Hince a 4 ohm load into a 625 ohm would equal a load on the amp of 156watts. Your 4ohm speaker when hooked up to the 25volt leg without ANY transformer would pose a 156.25 watt load on the amp. By the same token a load on the 70 volt side is figured as 70.7vX70.7v=4998ohms. The value of both 25volt and 70volt lines are to drive quantities of speakers and a heck of a lot of wire without problems. a 25volt line would drive a maximum of 625 speakers tapped at 1watt on the 25volt transformer. Do the math and you can see the value of the commercial speaker system as opposed to trying to series parallel 8 ohm speakers.
To answer your question...NO, do not use a 4 ohm speaker on the 25volt tap or the 70volt tap either. You would be better to put it on the 8ohm tap as opposed to anything else. Better yet use an 8ohm speaker.
Tube amps are more forgiving than any SS amp would ever be when it comes to overloading.
Joe
NO! Your units are all wrong. R = V/I, not V*V.If your PA (Public Address) system is 100W, then you'll have V^2/P = R = 70^2/100 = 49 ohms. The advantages to a 70V line are lower current = lower joule heating (I^2R loss) and a slightly easier way to match multiple loads.
Indeed, even a 4 ohm output will reach 70V - around 1.2kW in fact, probably suitable for a stadium. This likely would be served by many 32 or 64 ohm loads, each tapping a hundred or two watts.
Also, you DON'T "impose a load of n watts" on an amplifier. You impose a load resistance on it. The voltage the amplifier produces determines the power output.
There is nothing wrong with connecting a .2W PC speaker to a 500W amp, nor powering your 200W cabinets off a 50mW headphones amp. The only problem is that in the first case, background noise alone might blow the speaker (that represents noise about -30dB below full power output, not impossible), let alone any useful signal; while in the second case, the amplifier will be well into clipping distortion before you can even hear anything in the speakers (without your head in front of them). A less extreme form of the second example is ideal because amplifiers usually clip with no consequences, while speakers go over limits much less gracefully. Like, 100W speaker with 50W amp. Assuming the speaker is rated for continuous power.
Tim
NO! Your units are all wrong. R = V/I, not V*V.
Relax Tim!
I may have to take another stab at this in order to satify you. First of all when calculating the load on a 25volt line the figure 625ohms is used. The 625 ohms is a figure arrived at when figuring a 25volt line/load. This figure is the product of multiplying 25X25. Tim, please feel free to check this in any commercial Altec Lansing or EV material.
Now, if a 10 watt amplifier is used on a 25volt tap the maximum impedance load would be aproximately 62 ohms load on the line. This would be 625 ohms divided by 62ohms= 10.08 watts. Do you understand?
Now if the load was 50 ohms on a 70 volt line the load would be 100watts. Now this figure would be derived by dividing the square of 70.7 by 50 ohms. Tim this would be 70.7X70.7= divided by 50.
A 100 watt load in other words.
Now, if you impose a 8ohm speaker without a transformer on a 70.7 volt line the amplifier sees this a virtually a dead short. By the same token it is asking for trouble to connect a 4ohm or 8ohm speaker to a 25volt line.
Get real please!!!
I still stand correct in my previous post. Hooking up a 4ohm speaker without a transformer to the 25volt tap is incorrect. Hooking the 4 ohm speaker up to the 25volt tap and ground is having the amp see a load of 156watts. Tim, this figure is arrived by dividing 625by 4 ohms. I don't think the amp in question is quite large enough for this task. Do you?
Tim, hooking up a 4 ohm speaker to a 70.7 volt tap is equal to a load of 1249.6225 watts on an amp. Now Tim this is fine if the amplifier is large enough to support such a load.
Tim Wyatt
Do not hook up to the 25volt leg and ground as this WILL impose an overload to the amplifier. The less dangerous method would be to hook to the 8 ohm and ground or maybe better yet add a 4ohm resistor in series to the 4 ohm driver to arrive at an 8ohm load and then terminate to the 8 ohm leg and ground.
Joe
Relax Tim!
I may have to take another stab at this in order to satify you. First of all when calculating the load on a 25volt line the figure 625ohms is used. The 625 ohms is a figure arrived at when figuring a 25volt line/load. This figure is the product of multiplying 25X25. Tim, please feel free to check this in any commercial Altec Lansing or EV material.
Now, if a 10 watt amplifier is used on a 25volt tap the maximum impedance load would be aproximately 62 ohms load on the line. This would be 625 ohms divided by 62ohms= 10.08 watts. Do you understand?
Now if the load was 50 ohms on a 70 volt line the load would be 100watts. Now this figure would be derived by dividing the square of 70.7 by 50 ohms. Tim this would be 70.7X70.7= divided by 50.
A 100 watt load in other words.
Now, if you impose a 8ohm speaker without a transformer on a 70.7 volt line the amplifier sees this a virtually a dead short. By the same token it is asking for trouble to connect a 4ohm or 8ohm speaker to a 25volt line.
Get real please!!!
I still stand correct in my previous post. Hooking up a 4ohm speaker without a transformer to the 25volt tap is incorrect. Hooking the 4 ohm speaker up to the 25volt tap and ground is having the amp see a load of 156watts. Tim, this figure is arrived by dividing 625by 4 ohms. I don't think the amp in question is quite large enough for this task. Do you?
Tim, hooking up a 4 ohm speaker to a 70.7 volt tap is equal to a load of 1249.6225 watts on an amp. Now Tim this is fine if the amplifier is large enough to support such a load.
Tim Wyatt
Do not hook up to the 25volt leg and ground as this WILL impose an overload to the amplifier. The less dangerous method would be to hook to the 8 ohm and ground or maybe better yet add a 4ohm resistor in series to the 4 ohm driver to arrive at an 8ohm load and then terminate to the 8 ohm leg and ground.
Joe
burnedfingers said:
But your units ARE all wrong. Volts squared yields joules squared per coulomb squared (J^2/C^2), nothing more. Divided by resistance, however, it becomes joules per second. Resistance is in...joule-seconds per coulomb squared? I forget at the moment.
NOW you're doing it correctly. P=V^2/R.
Run the numbers. 1.2kW as I said would probably fit well in a stadium.
What token? To know if it would match we still need to know the power level. That's behind the very definition of voltage-based (rather than impedance) lines.
Run the numbers, with my equations or your own. You'll find that an 80W amp would power a 25V line quite nicely with a total of 8 ohms on the end. (I say total because the whole other point of these voltage lines is distribution over either long distances or multiple speakers.)
Also, assuming the amp is producing 25V on the 25V tap. Audio of a hi-fi nature will never be consistent so calling out voltages is pointless, especially without any distribution needed. Now obviously joe, JOE, JOE, the speaker isn't going to draw one hundred fifty-six watts from an amplifier which might be...30W? Where do the 126W come from?
Probably not. As such the impedance must not be matched correctly. So you'll have much less than maximum power output anyway. It may still be possible to operate the amplifier with the speaker on this tap but gain will be lower, distortion will be higher and clipping will come earlier (i.e. lower power).
Huh? I thought it was a dead short?
As for the other Tim, I suspect the amplifier is...20W? 40W? Whichever method you use, output power has to be known, Ohm's law says so. What's the back panel say, Tim?
Tim
But your units ARE all wrong. Volts squared yields joules squared per coulomb squared (J^2/C^2), nothing more. Divided by resistance, however, it becomes joules per second. Resistance is in...joule-seconds per coulomb squared? I forget at the moment. WoW you impressed me again!
Please check the formulas for figuring 25volt and 70.7 volt speaker lines.
The figures are as I stated. The impedance of 625 ohms for the 25volt line is correct as is the figure of 4998 ohms for a 70.7 volt line.
Throwing a 4 ohm speaker on a 25volt line is imposing a load of 4 ohms
on the amplifier or 625 divided by 4 = a load of 156 watts. This means it would take a 156 watt amplifier using the 25volt tap to drive this load.
quote:
Now, if you impose a 8ohm speaker without a transformer on a 70.7 volt line the amplifier sees this a virtually a dead short.
Tim, it would take a 1200watt amplifier to drive this load when tapped at 70.7 volts.
Quote:
Run the numbers. 1.2kW as I said would probably fit well in a stadium.
Tim, first of all you don't run main horns,(clusters)on the 70.7 volt tap.
The amplifier would run a 70.7volt line with a load of 1200watts. What I was trying to say was the 8 ohm speaker on the 70,7 volt tap will impose a load of 1200watts on the amplifier.
Quote:
Run the numbers, with my equations or your own. You'll find that an 80W amp would power a 25V line quite nicely with a total of 8 ohms on the end. (I say total because the whole other point of these voltage lines is distribution over either long distances or multiple speakers.)
Tim, I have no problem with this as it is correct. the 80 watt amplifier would drive a 7.8125 ohm load. Do the math Tim, a 4 ohm speaker would still require an amplifier of 156watts. Yes, Tim I do understand the concept of line distribution and multiple speakers.
Quote:
Also, assuming the amp is producing 25V on the 25V tap. Audio of a hi-fi nature will never be consistent so calling out voltages is pointless, especially without any distribution needed. Now obviously joe, JOE, JOE, the speaker isn't going to draw one hundred fifty-six watts from an
amplifier which might be...30W? Where do the 126W come from?
Did I say the speaker would draw 156watts? No, the amplifier will see the 4 ohm speaker as an overload. This would be too little impedance.
The amplifier will see the load as an overload unless the amplifier is large enough. Telling some one that is ok is just plain crazy. Unfortunately, it seems the logic you posess seems to be running free because I run into numerous know it alls at factories, grocery stores, and the like that seem to feel it is ok to attach a 8ohm speaker to the 70.7 volt system.
They wonder why it is distorted the amp runs hot and goes into thermal overload and why that 8 ohm speaker they added is the loud one and the
others can bearly be heard.
The idea of the step up transformer is to step up the voltage to either a 25volt line or a 70.7 volt line. This concept also requires that a step down transformer be attached to the speaker/s that are the load.
Please check the formulas for figuring 25volt and 70.7 volt speaker lines.
The figures are as I stated. The impedance of 625 ohms for the 25volt line is correct as is the figure of 4998 ohms for a 70.7 volt line.
Throwing a 4 ohm speaker on a 25volt line is imposing a load of 4 ohms
on the amplifier or 625 divided by 4 = a load of 156 watts. This means it would take a 156 watt amplifier using the 25volt tap to drive this load.
quote:
Now, if you impose a 8ohm speaker without a transformer on a 70.7 volt line the amplifier sees this a virtually a dead short.
Tim, it would take a 1200watt amplifier to drive this load when tapped at 70.7 volts.
Quote:
Run the numbers. 1.2kW as I said would probably fit well in a stadium.
Tim, first of all you don't run main horns,(clusters)on the 70.7 volt tap.
The amplifier would run a 70.7volt line with a load of 1200watts. What I was trying to say was the 8 ohm speaker on the 70,7 volt tap will impose a load of 1200watts on the amplifier.
Quote:
Run the numbers, with my equations or your own. You'll find that an 80W amp would power a 25V line quite nicely with a total of 8 ohms on the end. (I say total because the whole other point of these voltage lines is distribution over either long distances or multiple speakers.)
Tim, I have no problem with this as it is correct. the 80 watt amplifier would drive a 7.8125 ohm load. Do the math Tim, a 4 ohm speaker would still require an amplifier of 156watts. Yes, Tim I do understand the concept of line distribution and multiple speakers.
Quote:
Also, assuming the amp is producing 25V on the 25V tap. Audio of a hi-fi nature will never be consistent so calling out voltages is pointless, especially without any distribution needed. Now obviously joe, JOE, JOE, the speaker isn't going to draw one hundred fifty-six watts from an
amplifier which might be...30W? Where do the 126W come from?
Did I say the speaker would draw 156watts? No, the amplifier will see the 4 ohm speaker as an overload. This would be too little impedance.
The amplifier will see the load as an overload unless the amplifier is large enough. Telling some one that is ok is just plain crazy. Unfortunately, it seems the logic you posess seems to be running free because I run into numerous know it alls at factories, grocery stores, and the like that seem to feel it is ok to attach a 8ohm speaker to the 70.7 volt system.
They wonder why it is distorted the amp runs hot and goes into thermal overload and why that 8 ohm speaker they added is the loud one and the
others can bearly be heard.
The idea of the step up transformer is to step up the voltage to either a 25volt line or a 70.7 volt line. This concept also requires that a step down transformer be attached to the speaker/s that are the load.
Oil on troubled waters, or oil on the flames?
Gentlemen, it is conventional for 100V and 70V line systems to talk about a loudspeaker imposing a load of "x" Watts. If you look at the matching transformers (for the loudspeaker end), you find that the secondary may have 4 or 8 Ohm taps, but the primary is marked in terms of the power it will draw from the amplifier. This makes it easy for the user of a PA system (probably not a physicist) who knows that they have a 100W amplifier to avoid overloading said amplifier when they connect lots of loudspeakers in parallel. It's also handy for controlling loudspeaker directivity. By driving different proportions of power to identical loudspeakers in a line array, directivity can be adjusted at will.
However, V x V does not equal Ohms. The units are wrong, and it doesn't matter how many loudspeaker manufacturers make the claim.
Getting back to the original point, a 4 Ohm loudspeaker connected directly across a 70V line would only be correctly matched if the amplifier was rated at 1225W. Similarly, connecting to 25V line would require the amplifier to be rated at 156.25W. A push-pull pair of EL34 can stretch to 50W, precluding use of the 25V line output. Unfortunately, even loading the 8 Ohm output with 4 Ohms will cause the output power to fall drastically, and distortion will rise. You really need a true 8 Ohm loudspeaker.
Gentlemen, it is conventional for 100V and 70V line systems to talk about a loudspeaker imposing a load of "x" Watts. If you look at the matching transformers (for the loudspeaker end), you find that the secondary may have 4 or 8 Ohm taps, but the primary is marked in terms of the power it will draw from the amplifier. This makes it easy for the user of a PA system (probably not a physicist) who knows that they have a 100W amplifier to avoid overloading said amplifier when they connect lots of loudspeakers in parallel. It's also handy for controlling loudspeaker directivity. By driving different proportions of power to identical loudspeakers in a line array, directivity can be adjusted at will.
However, V x V does not equal Ohms. The units are wrong, and it doesn't matter how many loudspeaker manufacturers make the claim.
Getting back to the original point, a 4 Ohm loudspeaker connected directly across a 70V line would only be correctly matched if the amplifier was rated at 1225W. Similarly, connecting to 25V line would require the amplifier to be rated at 156.25W. A push-pull pair of EL34 can stretch to 50W, precluding use of the 25V line output. Unfortunately, even loading the 8 Ohm output with 4 Ohms will cause the output power to fall drastically, and distortion will rise. You really need a true 8 Ohm loudspeaker.
Thank you.
If it's 50W, since that's "stretching it", 40W is a good estimate (although...being a PA amp, the 50W might not be too far off); that 25V output might be 16 ohms or so... Then yes I think there would be 4 ohms between the 8 ohm and 25V taps. Although I can't seem to get the math to work out (1.4 ohms, um, no).
Tim
If it's 50W, since that's "stretching it", 40W is a good estimate (although...being a PA amp, the 50W might not be too far off); that 25V output might be 16 ohms or so... Then yes I think there would be 4 ohms between the 8 ohm and 25V taps. Although I can't seem to get the math to work out (1.4 ohms, um, no).
Tim
hi all,
I'll refer you to this link :
http://www.antrimtransformers.com/100V_Line.htm
By implication a 25V line output is 25V RMS at max amplifier power.
For a 4ohm load to be ideally matched to this the amplifier
power output would need to ~ 160W.
This seems to be high and this the case - line systems are
high impedance - this the whole point - speakers are tapped
off along the line with various power and hence volume settings
without resistive losses.
For 4 ohm to match a 100V line it would need to be a 2.5Kw
amplifier.
I can not make head nor tale of your posts.
A 100V line amplifier is arranged to have maximum output at 100V.
The amplifier output is specified - say 35 Watts.
You can then load this line to the total of number of Watts specified.
The speakers have 100V transformers that allow you to choose
the number of Watts drawn from the line and hence the relative
speaker volume.
Total number of watts drawn should not exceed the amplifier power,
otherwise you will start to get an impedance mismatch, drawing less
power causes load impedance to be higher which is not a problem.
Simple fact here is for an 80W amplifier the 8 ohm output
and 25V line output would be one and the same.
If your amplifier was 150W describing the 4 ohm output
as 25V line would be very bizarre.
So it it likely output is less than 50W and no output will drive 4 ohms.
sreten.
I'll refer you to this link :
http://www.antrimtransformers.com/100V_Line.htm
By implication a 25V line output is 25V RMS at max amplifier power.
For a 4ohm load to be ideally matched to this the amplifier
power output would need to ~ 160W.
This seems to be high and this the case - line systems are
high impedance - this the whole point - speakers are tapped
off along the line with various power and hence volume settings
without resistive losses.
For 4 ohm to match a 100V line it would need to be a 2.5Kw
amplifier.
I can not make head nor tale of your posts.
A 100V line amplifier is arranged to have maximum output at 100V.
The amplifier output is specified - say 35 Watts.
You can then load this line to the total of number of Watts specified.
The speakers have 100V transformers that allow you to choose
the number of Watts drawn from the line and hence the relative
speaker volume.
Total number of watts drawn should not exceed the amplifier power,
otherwise you will start to get an impedance mismatch, drawing less
power causes load impedance to be higher which is not a problem.
Simple fact here is for an 80W amplifier the 8 ohm output
and 25V line output would be one and the same.
If your amplifier was 150W describing the 4 ohm output
as 25V line would be very bizarre.
So it it likely output is less than 50W and no output will drive 4 ohms.
sreten.Formula
I think the formula P=EXE/Z should explain my point of view. This is Power equals voltage squared over Impedance. Therefore, E squared or 25X25=625. If the load imposed is 4 ohms this would be 625 divided by 4 or 156 watts.
By the same token, 70.7X70.7= 4998.49 over 4 ohms = 1249.6225 or P=1249.6225
To answer the Question. No, do not hook up to the 25Volt leg with the 4 ohm speaker. The reason as I have proved above using this formula.
concession...
In the case of a tube amplifier, the tube amplifier is a lot more forgiving that a SS amplifier would be. You could expect a SS amplifier to go belly up in a short amout of time. I have personally seen tube amplifiers run way overloaded for years and keep on ticking like a Timex watch.
I rest my case.
Joe
I think the formula P=EXE/Z should explain my point of view. This is Power equals voltage squared over Impedance. Therefore, E squared or 25X25=625. If the load imposed is 4 ohms this would be 625 divided by 4 or 156 watts.
By the same token, 70.7X70.7= 4998.49 over 4 ohms = 1249.6225 or P=1249.6225
To answer the Question. No, do not hook up to the 25Volt leg with the 4 ohm speaker. The reason as I have proved above using this formula.
concession...
In the case of a tube amplifier, the tube amplifier is a lot more forgiving that a SS amplifier would be. You could expect a SS amplifier to go belly up in a short amout of time. I have personally seen tube amplifiers run way overloaded for years and keep on ticking like a Timex watch.
I rest my case.
Joe
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