knightfly
GrouchyOldFartOnBatteries
John, I noticed this comment on your very informative site S.A.E. , and this seemed like the best place to answer;
"So you would expect that your standard electrical feed from your power supplier would be balanced. Well unfortunately here in Australia it's not. Sure we get a red positive and a black negative from the power companies transformer but by Australian regulations the electrician must link the negative to the earth so we become unbalanced. I understand that is not the system in the US which is why Marshall amps hum in OZ but don't in the US. I would be interested in any information I could receive on this matter from anyone from the US."
I hold two different electrical licences plus have over 20 years experience as an Industrial Control Instrumentation Tech, so can probably answer most of your questions about electrical as pertains to the U.S.
Firstly, you mentioned negative and positive leads in respect to mains power in oz - In actuality, doesn't oz use 240 volt, 50 hZ AC power? If so,here in the US the situation for most users is similar. Our power is usually 120 volt, 60 hZ, but that too is earthed on one side, so you have one lead at ground potential and one lead at 120 volts 60 hZ. Our color coding is also different, white being neutral, or grounded, and black being the hot lead. Green is normally used for earth. Current normally flows thru the hot and neutral leads, with the green earth lead being a (supposedly) non-current carrying reference. The only balanced power usually found in homes is 240 volt "single phase" power, which consists of a second 120 VAC feed that is 180 degrees out of phase with the first. With a meter, you would measure 120 VAC from either wire to common, or earth ground, but between the two hot leads you would measure 240 VAC, since one is going negative while the other is going positive. This is brought into the home electrical panel, and split into two busses, which are alternately used to wire 120 volt circuits to ground. The only devices in the home which normally use this 240 volt power are high current devices, such as cook stoves, clothes dryers, water heaters and some electrical heating units. Our 3-phase power is normally reserved for high power industrial use, and each phase is 120 degrees from the other two. This means that normal single phase equipment doesn't like the power derived from a 3-phase system too well, because the voltage between phases and ground is too low. Your description of the uses for 3-phase in a studio is probably used in large sound facilities here, I'm not sure. My experience with electrical has not been concurrent with my studio experience, other than at my own project studio which will eventually benefit from the other areas of your S.A.E. site, thank you very much. Virtually all studio gear for US that I'm aware of runs off the un-balanced 120 VAC, partly because of safety considerations. Apparently the "powers that be" decided that 120 volts was safer to be shocked from than 240 volts, so everything I've ever seen runs from that source. Therefore your diagram of the Star Grounding System also applies here -
However, there is a "New Kid on the Block", so to speak -
Balanced Technical Power.
There is a small but growing company here in my home state of Oregon that has been instrumental in getting the National Electrical Code amended to allow balanced power to be used in technical installations where necessary for noise control, and they make systems from home stereo size up to large 3-phase commercial systems. They do offer models that take 208/240 volt 3-phase power and output 120 volts balanced. The 120 volt models are basically a precision center-tapped transformer that takes in un-balanced 120 VAC and outputs a center-tapped ground and two 60 volt "phases", between which you get 120 VAC. The difference is that any current flowing in the ground is canceled out on the power leads, similar to balanced 600 ohm audio lines.
The downside is expense - a 1500 watt system costs about $1250 US, and the price goes up quickly with options and size. The other downside is that in order to use balanced power with a UPS, the UPS must be sized large enough to run the balanced line transformer and all the studio gear plugged into it. A typical combo would be a 2200 VA UPS, such as APC, at about $800 US, and a 15 amp transformer at about $1250 US, so we're looking at about $2000 US or slightly more, for a non headbanger type project studio (meaning without tri-amped 2 kilowatt speaker systems).
The upside is this: reported noise floor improvements in typical project studios (using both balanced and unbalanced gear in combination) run normally in excess of 12 dB, just by unplugging everything from the wall and inserting a balanced power transformer.
The company I referred to is called Equi=Tech, and their site is an education in itself. Here is a link, be prepared to spend some time if you don't want to miss anything -
http://www.equitech.com/
If you had already answered your question put forth on your site, please do not read the above :=) Oops, too late - Just kidding, hope this helps a few people... Steve
"So you would expect that your standard electrical feed from your power supplier would be balanced. Well unfortunately here in Australia it's not. Sure we get a red positive and a black negative from the power companies transformer but by Australian regulations the electrician must link the negative to the earth so we become unbalanced. I understand that is not the system in the US which is why Marshall amps hum in OZ but don't in the US. I would be interested in any information I could receive on this matter from anyone from the US."
I hold two different electrical licences plus have over 20 years experience as an Industrial Control Instrumentation Tech, so can probably answer most of your questions about electrical as pertains to the U.S.
Firstly, you mentioned negative and positive leads in respect to mains power in oz - In actuality, doesn't oz use 240 volt, 50 hZ AC power? If so,here in the US the situation for most users is similar. Our power is usually 120 volt, 60 hZ, but that too is earthed on one side, so you have one lead at ground potential and one lead at 120 volts 60 hZ. Our color coding is also different, white being neutral, or grounded, and black being the hot lead. Green is normally used for earth. Current normally flows thru the hot and neutral leads, with the green earth lead being a (supposedly) non-current carrying reference. The only balanced power usually found in homes is 240 volt "single phase" power, which consists of a second 120 VAC feed that is 180 degrees out of phase with the first. With a meter, you would measure 120 VAC from either wire to common, or earth ground, but between the two hot leads you would measure 240 VAC, since one is going negative while the other is going positive. This is brought into the home electrical panel, and split into two busses, which are alternately used to wire 120 volt circuits to ground. The only devices in the home which normally use this 240 volt power are high current devices, such as cook stoves, clothes dryers, water heaters and some electrical heating units. Our 3-phase power is normally reserved for high power industrial use, and each phase is 120 degrees from the other two. This means that normal single phase equipment doesn't like the power derived from a 3-phase system too well, because the voltage between phases and ground is too low. Your description of the uses for 3-phase in a studio is probably used in large sound facilities here, I'm not sure. My experience with electrical has not been concurrent with my studio experience, other than at my own project studio which will eventually benefit from the other areas of your S.A.E. site, thank you very much. Virtually all studio gear for US that I'm aware of runs off the un-balanced 120 VAC, partly because of safety considerations. Apparently the "powers that be" decided that 120 volts was safer to be shocked from than 240 volts, so everything I've ever seen runs from that source. Therefore your diagram of the Star Grounding System also applies here -
However, there is a "New Kid on the Block", so to speak -
Balanced Technical Power.
There is a small but growing company here in my home state of Oregon that has been instrumental in getting the National Electrical Code amended to allow balanced power to be used in technical installations where necessary for noise control, and they make systems from home stereo size up to large 3-phase commercial systems. They do offer models that take 208/240 volt 3-phase power and output 120 volts balanced. The 120 volt models are basically a precision center-tapped transformer that takes in un-balanced 120 VAC and outputs a center-tapped ground and two 60 volt "phases", between which you get 120 VAC. The difference is that any current flowing in the ground is canceled out on the power leads, similar to balanced 600 ohm audio lines.
The downside is expense - a 1500 watt system costs about $1250 US, and the price goes up quickly with options and size. The other downside is that in order to use balanced power with a UPS, the UPS must be sized large enough to run the balanced line transformer and all the studio gear plugged into it. A typical combo would be a 2200 VA UPS, such as APC, at about $800 US, and a 15 amp transformer at about $1250 US, so we're looking at about $2000 US or slightly more, for a non headbanger type project studio (meaning without tri-amped 2 kilowatt speaker systems).
The upside is this: reported noise floor improvements in typical project studios (using both balanced and unbalanced gear in combination) run normally in excess of 12 dB, just by unplugging everything from the wall and inserting a balanced power transformer.
The company I referred to is called Equi=Tech, and their site is an education in itself. Here is a link, be prepared to spend some time if you don't want to miss anything -
http://www.equitech.com/
If you had already answered your question put forth on your site, please do not read the above :=) Oops, too late - Just kidding, hope this helps a few people... Steve
