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Power Isolation Transformer
Power Isolation Transformer
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Old 17th January 2020, 10:56 PM   #1
Diyengineer is offline Diyengineer  United States
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Default Power Isolation Transformer

Hi,

Are there any opinions on using power isolation transformers, either toroid or EI type, in a amplifier build? I’ve read some people say there’s some difference and that some say there’s none.

Not sure if there would be any benefit to using one.

Thanks
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Old 17th January 2020, 11:43 PM   #2
trobbins is offline trobbins  Australia
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What have you read and can you summarise what you appreciate are benefits and if you understand why they are benefits?

I assume you are talking about an external transformer from your amplifier build (and that your amplifier build would include an internal power transformer)?
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Old 17th January 2020, 11:46 PM   #3
wg_ski is offline wg_ski  United States
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The biggest “problem” is the 120 volt non-center-tapped secondary. If you’re building solid state, that limits you to a single 160-ish volt supply which means a very large capacitor coupled or even larger bridged amplifier. If that floats your boat, it will work fine. Smaller trafos work quite well to build tube amps, either running off 160 or so Volts or 320 with a doubler.

A 240 to 240CT (120-0-120) may be operated from 120 volts to give 60-0-60 or +/-84 V. You do not get full power rating, as you are limited by secondary current. You end up with a lot of magnetic headroom and it runs very quiet. I have several amps with these in them. While I would never pay full price for a transformer to be used this way, if you find one cheap it’s a good choice. A 1 to 2 KVA makes a nice 250W/ch amp.

I just bought two 110 to 480v 900VA EI core from Skycraft. Both slightly different but equally useable. Not your typical isolation transformer, but in the same general family. Makes 650 volt B+. Can run a lot of KT88s (or sweep tubes) with those.
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Old 18th January 2020, 12:06 AM   #4
TonyTecson is offline TonyTecson  Philippines
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Location: Maybunga, Pasig City
did it three years in a row 2016, 2017, 2018.....
rated at least 1000 volt- amperes,
240 volt primary to 240 volt secondary,
we used them in audio shows at the Dusit Thani Hotel, a downtown hotel...
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Old 18th January 2020, 02:15 AM   #5
Diyengineer is offline Diyengineer  United States
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I’ve attached a datasheet for the type of transformer I’m referring to. I read that these will potentially filter out EMI and harmonics that might exist on the line power coming in. This would also be installed internally on an amp build.

From what I could find on the subject in some older posts on different forums, a couple people said they make some improvement, and some claimed no real difference.
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Last edited by Diyengineer; 18th January 2020 at 02:18 AM.
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Old 18th January 2020, 02:45 AM   #6
carlthess40 is online now carlthess40  United States
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Maybe this will help people see the file easier
Adjustments.jpg
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Old 18th January 2020, 03:06 AM   #7
wg_ski is offline wg_ski  United States
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Ok, using it for power conditioning as opposed to using one *as* the power transformer. It can make a LOT of improvement if you have noisy corrupt grid power. Covers a multitude of sins.
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Old 18th January 2020, 03:59 AM   #8
AllenB is offline AllenB  Australia
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Power Isolation Transformer
Quote:
Originally Posted by Diyengineer View Post
these will potentially filter out EMI and harmonics
It could be said that an EI would do this even better. Not that it couldn't be taken care of either way.
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Old 18th January 2020, 05:26 AM   #9
trobbins is offline trobbins  Australia
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diy, what power supply are you using in your amp build? Will it include a power transformer similar to what you have linked to?

I'd anticipate you won't get any benefit from 'building in' that extra transformer, and it is quite likely that you will get noticeably worse performance due to causes such as mains DC overloading your toroidal transformer, and stray hum and noise coupling in to your amp circuit from the extra transformer due to its location and wiring.

Note that that particular toroidal transformer does not include an electrostatic shield between primary and secondary windings.

Last edited by trobbins; 18th January 2020 at 05:28 AM.
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Old 18th January 2020, 10:49 AM   #10
Diyengineer is offline Diyengineer  United States
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Quote:
Originally Posted by trobbins View Post
I'd anticipate you won't get any benefit from 'building in' that extra transformer, and it is quite likely that you will get noticeably worse performance due to causes such as mains DC overloading your toroidal transformer, and stray hum and noise coupling in to your amp circuit from the extra transformer due to its location and wiring.

Note that that particular toroidal transformer does not include an electrostatic shield between primary and secondary windings.
Would the possible “worse performance” be because of no electrostatic shield? That company also makes toroids with electrostatic shields for a few bucks more.

Also note, I’m just trying to get a general consensus on designing in some power conditioning into an amp or preamp itself. Other than just using a filtered IEC and such. Thanks guys.
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