Power Isolation Transformer

wg_ski

Member
2007-10-10 5:21 pm
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.
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
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...
 

Attachments

  • IMG_7972 (2).JPG
    IMG_7972 (2).JPG
    513.2 KB · Views: 245
  • IMG_8024.JPG
    IMG_8024.JPG
    583.5 KB · Views: 238
  • IMG_8690.JPG
    IMG_8690.JPG
    402.2 KB · Views: 242
  • IMG_8689.jpg
    IMG_8689.jpg
    911.7 KB · Views: 241
  • IMG_1199.jpg
    IMG_1199.jpg
    977.4 KB · Views: 240
  • IMG_1198.jpg
    IMG_1198.jpg
    984.4 KB · Views: 92
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.
 

Attachments

  • 749.1202.PDF
    369.8 KB · Views: 44
Last edited:
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:
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.
 
Would the possible “worse performance” be because of no electrostatic shield?
No. Perhaps if you google toroidal power transformers and DC issues, and also on hum/coupling between power transformers and wiring and sensitive parts of amplifier circuits.

Are you trying to 'design in' some mains filtering because you are having existing problems with your previously designed gear? It is good to elaborate on why you have this 'need', as sometimes posters seem to have a solution in mind when there is no problem.
 
I have experience with a very large toroidal line isolation transformer I think rated 10kVA (it's in an inaccessible position now to read the tag) ~16" diameter ~3.5" high ~66 lbs designed for 60Hz line (US). Subjectively very effective in reducing line noise in an audio system. It was so effective with improving sound quality, I picked up a few for friends and family. All are very pleased with the improvement, and continue to use them, and transport them when moving. I still have a couple available. If interest, I can post over in the marketplace.
 
Last edited:
Correction to the post above. Rating is 3KVA 60Hz 120V primary/secondary 80 deg C rise, Insulation class F (which is 180 deg C), leakage 10 microamps max. Manufactured by Electromagnetic Industries 541-1-1, similar in appearance to the green one on eBay auction. Small fraction of $.
 
Last edited:
Subjectively very effective in reducing line noise in an audio system. It was so effective with improving sound quality, I picked up a few for friends and family. All are very pleased with the improvement, and continue to use them, and transport them when moving. I still have a couple available. If interest, I can post over in the marketplace.
Your post sure reads like Publicity and guess should have been posted straight in the sales section.