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Old 31st December 2002, 03:34 PM   #1
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Smile Isolation Transformer Use???

Hello,

I have come across a Hammond 500va isolation transformer. I do not truly understand the function of it.

Can it be used for audio gear? and will it improve sound and why?

Any experiences with isolation transformers would be appreciated.

Thanks

KevinLee
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Old 31st December 2002, 04:11 PM   #2
sam9 is offline sam9  United States
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Default Bench safety

If it is what I think it is, it is used when working on electronic equipment when the the design of the equipment is such that the mains current isused directly. I.e., the equipment being worked on has no transformer of it's own. Working on such a piece of equipment is hazardous because anything you couch is directly connected to the mains voltage. This is rare in currently maufactured audio gear, but I understand it was common in the past, especially with regard to old radios and TV's. (New TV's may still be like this -- I'm not familiar with their insides.)

Thus is is a piece of safety equipment that should be used in the circumstances described.

However, it posses a danger if misused, namely by plugging test equipment into one. Never, plug test equipment especially scopes in to an isolation transformer as there will be no ground (it will be "floated"). I once worked at a place where this was such a strong rule, doing so was a first time firing offence.
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Old 31st December 2002, 08:47 PM   #3
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An isolation transformer is used to remove the DC ground connection to the AC power supply lines. It is simply a 1:1 transformer (usually same output voltage as input voltage). These are used when working on AC/DC type radios and TVs Which have no transformer and therefore can have a "hot" chassis depending on how you plug them in to the power outlet on the wall. In this situation, the isolation transformer is used to protect the technician doing the work. Without the transformer, if he were to simultaneously touch a "hot" chassis and a grounded piece of test equipment, he would receive a nasty shock.

Isolation transformers are also used on test equipment when you need to make a measurement that is not referenced to ground. Sometimes a circuit has a DC bias on the "ground" side and if you connect the ground of a scope probe to it, it will short the DC supply and maybe damage or destroy the circuit under test. It will certainly screw up the measurement. If you plug the scope into an isolation transformer, you break the DC connection from scope ground back to AC power system ground, and the measurement can be made safely.

NEVER use a variac in place of an isolation transformer. They are autotransformers and provide NO isolation from the AC power system at all.

MR
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Old 1st January 2003, 08:20 AM   #4
Duo is offline Duo  Canada
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I use a 5000va isolation trannie for my whole audio system. It actually improves the sound a lot and I have little trouble with ground loops as well. Depending on what you want to do, you might try your hammond on a cd transport or any amplifier that draws under 500W from the transformer. The design of an ac isolation transformer is quite effective in absorbing high frequency transients in the ac line and thus may clean up the noise floor on your system. If you had a saturation core transformer, it would do an even more effective job of eliminating noise and it would also regulate the voltage during surges and brownouts. These saturation transformers are, however, difficult to find, especially if you want one capable of high power.

Experiment a bit and see what you like most about your hammond, perhaps you'll find just the perfect piece of audio equipment to use it with.
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Old 1st January 2003, 08:57 AM   #5
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Quote:
Originally posted by MRehorst
Isolation transformers are also used on test equipment when you need to make a measurement that is not referenced to ground. Sometimes a circuit has a DC bias on the "ground" side and if you connect the ground of a scope probe to it, it will short the DC supply and maybe damage or destroy the circuit under test. It will certainly screw up the measurement. If you plug the scope into an isolation transformer, you break the DC connection from scope ground back to AC power system ground, and the measurement can be made safely.
This can be a very dangerous practice as you may find that the scope is suddenly floating thousands of volts above ground. DO NOT attempt this unless you are suitably qualified and understand all of the risks involved.
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Old 1st January 2003, 10:04 AM   #6
Duo is offline Duo  Canada
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It is very true that using test equipment on an isolation tranny can be quite dangerous if done improperly. It really depends on what you are trying to do. It seems that in the case of audio equipment, there aren't many risks as long as proper grounding and isolating schemes are employed. I found that with my iso tranny in place, there were less dangerous voltage potentials from ground to certain points in general equipment. This may not apply though when things like scope leads are left to float.
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Old 1st January 2003, 02:28 PM   #7
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Quote:
Originally posted by Duo
I use a 5000va isolation trannie for my whole audio system. It actually improves the sound a lot and I have little trouble with ground loops as well. Depending on what you want to do, you might try your hammond on a cd transport or any amplifier that draws under 500W from the transformer. The design of an ac isolation transformer is quite effective in absorbing high frequency transients in the ac line and thus may clean up the noise floor on your system. If you had a saturation core transformer, it would do an even more effective job of eliminating noise and it would also regulate the voltage during surges and brownouts. These saturation transformers are, however, difficult to find, especially if you want one capable of high power.

Experiment a bit and see what you like most about your hammond, perhaps you'll find just the perfect piece of audio equipment to use it with.
Try it on the digital gear first, esp if it's an EI core, as the limited bandwidth of most EI trannies will reduce the amount of rubbish being returned to the mains sytem in your house by your digital components, which can get back into other components.

One of the best investments you can make is to buy a big surplus 5kVA+ iso trans (try metal recycler) and have your entire system run through it from the main fusebox (check local regulations, and get an electrician to wire it up). Cost might only be a couple of hundred bucks total. Having done the tests and seen the difference in the mains spectrum, bith with and without a big iso trans on an HP spectrum analyser, its a hell of a good investment.

Cheers
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Old 1st January 2003, 05:35 PM   #8
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Default Floating test equipment.

Quote:
Originally posted by AudioFreak


This can be a very dangerous practice as you may find that the scope is suddenly floating thousands of volts above ground. DO NOT attempt this unless you are suitably qualified and understand all of the risks involved.
Well, this is done as needed. I've done it myself from time to time. However, you need to be aware of the risks involved.

Usually when floating test equipment, it best to measure the level of float voltage before you start, unless you know what it is. Somewhere on tektronix web site, they specify you can float scopes by +- 30V. (This is probably because 30V is considered safe). However, if done carefully, higher voltages can be floated. Usually, the equipment can be isolated, and then use the test equipment ground to move the ground potential where ever it is needed. Again, you need to be careful.

Also keep in mind that sometimes even an isolation transformer isn't enough. TV picture tubes usually run around 25 kilo volts. If your transformer is rated for 2kV isolation, it is possible for the 25kV to actually blow through the isolastion transformer. Most transformers are only rated for a couple of KV isolation. So there are still risks involved. (However, you shouldn't really be measuring the 25Kv with a scope anyway )

FYI, Most modern TV tubes are also the capacitor used for filtering the flyback, and even when off can be charged to 25kV. Make sure the tube is discharged before removing the high voltage lead.

The bottom line when working on with ANY electrical equipment is if you don't know, don't!

-Dan
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Old 4th January 2003, 03:54 AM   #9
wheezer is offline wheezer  United States
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I would check with Hammond and find out the winding ratio and the number of primary and secondary windings.
If it's at least 1:1, it's great for audio gear!
As Brett suggests, try it on the grungy stuff, DIGITAL.
Do not connect the CT. This defeats the purpose of Isolation.
THEN, providing it's an EI, if it has dual primaries and dual secondaries, wire it up in Balanced Power for some real improvement.
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Old 4th January 2003, 04:12 AM   #10
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Wheezer,

I am very interested in your comments!.

The transformer in question is a Hammond 171E. I could not tell from the website if it has dual primary & secondaries.

Any help would be appreciated on how to determine this, and also how to wire it for balanced power if it can be done.

Cheers

KevinLee
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