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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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70volt transformer
I picked up a 100 watt matching transformer at a radio show for 2.00
today. The primary is 4 ohms and the secondary is rated "70 volts 100 watts". Has anyone ever used one of these so that a conventional amplifier could be used on a 70 V line? Could anyone think of any problems that could be associated with doing this? Thanks, Lenny |
#2
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70volt transformer
"klem kedidelhopper" I picked up a 100 watt matching transformer at a radio show for 2.00 today. The primary is 4 ohms and the secondary is rated "70 volts 100 watts". Has anyone ever used one of these so that a conventional amplifier could be used on a 70 V line? Could anyone think of any problems that could be associated with doing this? Thanks, Lenny ** You posted the same asinine question a month ago and it was answered. Shame it was not what you wanted to hear. The term " conventional amplifier " simply has no meaning. Your 70V line tranny would be OK with a valve amplifier. .... Phil |
#3
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70volt transformer
On 6/16/2012 7:34 PM, klem kedidelhopper wrote:
I picked up a 100 watt matching transformer at a radio show for 2.00 today. The primary is 4 ohms and the secondary is rated "70 volts 100 watts". Has anyone ever used one of these so that a conventional amplifier could be used on a 70 V line? Could anyone think of any problems that could be associated with doing this? Thanks, Lenny It will work OK, if it's a good transformer. It will convert a 4 ohm output to 50 ohms. 5000/100 = 50 We did this back in the '70s when 'smart' AKA 'cheapskate' customers bought the wrong equipment, then they wanted the system fixed. |
#4
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70volt transformer
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#5
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70volt transformer
On 6/16/2012 10:22 PM, Charles wrote:
http://www.rane.com/note136.html What a long way to get to a place, when you can simply do the math in your head. The third schematic won't work, because the drawing shows both amps in phase. There will be 0 volts at the outputs of the amps, as drawn. I've also seen a system with severe distortion and overheating amps that were wired in parallel, but out of phase. I was doing this in the early '60s, and owned a commercial sound business for a decade after that. Web pages like that are pure marketing, nothing more. 350 watts loss in a 1 KW system is **** poor design. It was written by a marketing dweeb, who thinks that they are a design engineer. The amps or transformers are simple, and three formulas cover 25, 70.7 & 100 volt systems: 25*25 = 625 ohms per watt. A 100 watt amp would be 6.25 ohms. 70.7*70.7 = 5000 ohms per watt. A 100 watt amp would be 50.0 ohms. 100*100 = 10,000 ohms per watt. A 100 watt amp would be 100 ohms. You use the ohms/watt over the desired watts and it gives you the load impedance. Or just total all the loads and be within +/- 20% of the amplifier's rated output. This has been done for almost 100 years and it's still a valid method. I always preferred the error to be on the +20% side so a few additional speakers could be added at a later date. This is no more rocket science than wiring in any power distribution system is. KISS, so people don't clutter their minds with useless classroom type crap. You could waste days doing that way, instead of minutes, and that's a great way to price yourself out of business. Instead, know what you have to work with, and carry everything you need to the job in as few trips as possible. Have extra parts and hardware on hand. Stopping work to go buy a couple screws or electrical box can cost you several hours of lost productivity. Very few customers are foolish enough to sign a T&M contract. |
#6
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70volt transformer
On Jun 17, 5:32*am, "Michael A. Terrell"
wrote: On 6/16/2012 10:22 PM, Charles wrote: http://www.rane.com/note136.html * * What a long way to get to a place, when you can simply do the math in your head. *The third schematic won't work, because the drawing shows both amps in phase. *There will be 0 volts at the outputs of the amps, as drawn. I've also seen a system with severe distortion and overheating amps that were wired in parallel, but out of phase. *I was doing this in the early '60s, and owned a commercial sound business for a decade after that. * * Web pages like that are pure marketing, nothing more. *350 watts loss in a 1 KW system is **** poor design. *It was written by a marketing dweeb, who thinks that they are a design engineer. * * The amps or transformers are simple, and three formulas cover 25, 70.7 & 100 volt systems: * * * 25*25 = 625 ohms per watt. *A 100 watt amp would be 6.25 ohms. 70.7*70.7 = 5000 ohms per watt. *A 100 watt amp would be 50.0 ohms. 100*100 = 10,000 ohms per watt. *A 100 watt amp would be 100 ohms. * * You use the ohms/watt over the desired watts and it gives you the load impedance. *Or just total all the loads and be within +/- 20% of the amplifier's rated output. *This has been done for almost 100 years and it's still a valid method. *I always preferred the error to be on the +20% side so a few additional speakers could be added at a later date.. * *This is no more rocket science than wiring in any power distribution system is. * * KISS, so people don't clutter their minds with useless classroom type crap. *You could waste days doing that way, instead of minutes, and that's a great way to price yourself out of business. *Instead, know what you have to work with, and carry everything you need to the job in as few trips as possible. *Have extra parts and hardware on hand. Stopping work to go buy a couple screws or electrical box can cost you several hours of lost productivity. *Very few customers are foolish enough to sign a T&M contract. So are you saying that if I calculate my total impedance, or rather total load in watts, (all my speakers/transformers) that are in parallel across this amplifier, depending on how the total load shakes out I may be able to operate this parallel distribution circuit directly off the 4 or 8 ohm tap? Lenny |
#7
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70volt transformer
On 6/17/2012 10:50 AM, klem kedidelhopper wrote:
On Jun 17, 5:32 am, "Michael A. wrote: On 6/16/2012 10:22 PM, Charles wrote: http://www.rane.com/note136.html What a long way to get to a place, when you can simply do the math in your head. The third schematic won't work, because the drawing shows both amps in phase. There will be 0 volts at the outputs of the amps, as drawn. I've also seen a system with severe distortion and overheating amps that were wired in parallel, but out of phase. I was doing this in the early '60s, and owned a commercial sound business for a decade after that. Web pages like that are pure marketing, nothing more. 350 watts loss in a 1 KW system is **** poor design. It was written by a marketing dweeb, who thinks that they are a design engineer. The amps or transformers are simple, and three formulas cover 25, 70.7& 100 volt systems: 25*25 = 625 ohms per watt. A 100 watt amp would be 6.25 ohms. 70.7*70.7 = 5000 ohms per watt. A 100 watt amp would be 50.0 ohms. 100*100 = 10,000 ohms per watt. A 100 watt amp would be 100 ohms. You use the ohms/watt over the desired watts and it gives you the load impedance. Or just total all the loads and be within +/- 20% of the amplifier's rated output. This has been done for almost 100 years and it's still a valid method. I always preferred the error to be on the +20% side so a few additional speakers could be added at a later date. This is no more rocket science than wiring in any power distribution system is. KISS, so people don't clutter their minds with useless classroom type crap. You could waste days doing that way, instead of minutes, and that's a great way to price yourself out of business. Instead, know what you have to work with, and carry everything you need to the job in as few trips as possible. Have extra parts and hardware on hand. Stopping work to go buy a couple screws or electrical box can cost you several hours of lost productivity. Very few customers are foolish enough to sign a T&M contract. So are you saying that if I calculate my total impedance, or rather total load in watts, (all my speakers/transformers) that are in parallel across this amplifier, depending on how the total load shakes out I may be able to operate this parallel distribution circuit directly off the 4 or 8 ohm tap? Lenny You could, but at higher power loss. But you lose the isolation provided by transformers. A single wire shorted to ground won't take down the system, and a nearby lightning strike won't fry the amplifier, due to that isolation. That's the whole reason for the transformers, and you use less wire than trying to run a series/parallel mess. You can run the 70.7 volt wiring in daisy chain, star or any convenient pattern. I used to run rows daisy chain, and star from the amp to each cluster of speakers. With today's cost of decent wire, the transformers are cheap by comparison. Here is a Bogen design guide that might help you with the concepts: http://www.bogen.com/support/product...fs/SysDsgn.pdf |
#8
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70volt transformer
On Sun, 17 Jun 2012 05:32:47 -0400, "Michael A. Terrell"
wrote: On 6/16/2012 10:22 PM, Charles wrote: http://www.rane.com/note136.html What a long way to get to a place, when you can simply do the math in your head. The third schematic won't work, because the drawing shows both amps in phase. There will be 0 volts at the outputs of the amps, as drawn. I've also seen a system with severe distortion and overheating amps that were wired in parallel, but out of phase. I was doing this in the early '60s, and owned a commercial sound business for a decade after that. Web pages like that are pure marketing, nothing more. 350 watts loss in a 1 KW system is **** poor design. It was written by a marketing dweeb, who thinks that they are a design engineer. The amps or transformers are simple, and three formulas cover 25, 70.7 & 100 volt systems: Oooh, i have a units issue he V=IZ P=VI Full signal voltage system relates as: V^2/P = IZIZ/IZI = Z 25*25 = 625 ohms per watt. A 100 watt amp would be 6.25 ohms. Make that watt*ohms 70.7*70.7 = 5000 ohms per watt. A 100 watt amp would be 50.0 ohms. 100*100 = 10,000 ohms per watt. A 100 watt amp would be 100 ohms. You use the ohms/watt over the desired watts and it gives you the load impedance. Or just total all the loads and be within +/- 20% of the amplifier's rated output. This has been done for almost 100 years and it's still a valid method. I always preferred the error to be on the +20% side so a few additional speakers could be added at a later date. This is no more rocket science than wiring in any power distribution system is. The only issue is just how high power, at 10 kW not bad, at 1 MW power distribution becomes incorporated. At 1 MW the power distribution system for the PA system (many amplifiers) itself is in arc flash hazard territory, very not funny. KISS, so people don't clutter their minds with useless classroom type crap. You could waste days doing that way, instead of minutes, and that's a great way to price yourself out of business. Instead, know what you have to work with, and carry everything you need to the job in as few trips as possible. Have extra parts and hardware on hand. Stopping work to go buy a couple screws or electrical box can cost you several hours of lost productivity. Very few customers are foolish enough to sign a T&M contract. |
#9
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70volt transformer
On 6/20/2012 12:14 AM, josephkk wrote:
On Sun, 17 Jun 2012 05:32:47 -0400, "Michael A. Terrell" wrote: On 6/16/2012 10:22 PM, Charles wrote: http://www.rane.com/note136.html What a long way to get to a place, when you can simply do the math in your head. The third schematic won't work, because the drawing shows both amps in phase. There will be 0 volts at the outputs of the amps, as drawn. I've also seen a system with severe distortion and overheating amps that were wired in parallel, but out of phase. I was doing this in the early '60s, and owned a commercial sound business for a decade after that. Web pages like that are pure marketing, nothing more. 350 watts loss in a 1 KW system is **** poor design. It was written by a marketing dweeb, who thinks that they are a design engineer. The amps or transformers are simple, and three formulas cover 25, 70.7& 100 volt systems: Oooh, i have a units issue he V=IZ P=VI Full signal voltage system relates as: V^2/P = IZIZ/IZI = Z The amplifiers are rated at full power, continuous service, with a sine wave that the Constant voltage out. 25*25 = 625 ohms per watt. A 100 watt amp would be 6.25 ohms. Make that watt*ohms 70.7*70.7 = 5000 ohms per watt. A 100 watt amp would be 50.0 ohms. 100*100 = 10,000 ohms per watt. A 100 watt amp would be 100 ohms. You use the ohms/watt over the desired watts and it gives you the load impedance. Or just total all the loads and be within +/- 20% of the amplifier's rated output. This has been done for almost 100 years and it's still a valid method. I always preferred the error to be on the +20% side so a few additional speakers could be added at a later date. This is no more rocket science than wiring in any power distribution system is. The only issue is just how high power, at 10 kW not bad, at 1 MW power distribution becomes incorporated. At 1 MW the power distribution system for the PA system (many amplifiers) itself is in arc flash hazard territory, very not funny. A properly designed high power sound system uses multiple amplifiers, and usually distributed to minimize power loss by placing each amp near a cluster of speakers. Then one amp feeds all the remote amps at the same distribution voltage. It is then matched to the line in of the power amps. Transformer isolation reduces chances of lightning damage. The worst I ever saw was at an amusement park where some clown put all the amps at on end of the park, and ran overhead and buried 70.7 volt lines all over the park. Some runs were over two miles. On top of that, all of the amplifier inputs and outputs were paralleled, and they used those old cheap 300 ohm TV antenna knife switches to connect or disconnect each amplifier for troubleshooting. It was no wonder they lost amplifiers on a regular basis. The system would get very distorted, so they would start flipping switches till it cleared up, then add the standby amp, if it wasn't away being repaired. This is the type switch I'm talking about. http://www.mcmelectronics.com/conten.../s4/26-790.jpg The local Lockheed-Martin facility has over 10 KW distributed audio that I understand is a complete hairball. One amp feeding the next in a daisy chain, and from building to building. Speaker wires run all over the place, and not always to the closest amp. Then the work space has been modified repeatedly for decades. I ran into the head of maintenance one day and overheard him talking with one of his techs about the mess and tried to explain how it work, then realized I was talking to a couple electricians. KISS, so people don't clutter their minds with useless classroom type crap. You could waste days doing that way, instead of minutes, and that's a great way to price yourself out of business. Instead, know what you have to work with, and carry everything you need to the job in as few trips as possible. Have extra parts and hardware on hand. Stopping work to go buy a couple screws or electrical box can cost you several hours of lost productivity. Very few customers are foolish enough to sign a T&M contract. |
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