Off the shelf double-shielded transformer - Page 1
Forum section: electronics / projects

author: ezalys
author_rank: Frequent Contributor
timestamp: March 20, 2022, 01:04:38 am
content: Is there anywhere that sells a double-faraday-shielded 120V -> +15/-15 transformer? 100 mA current minimum on both rails, ideally 200 mA or more. I'm working on an application that's particularly sensitive to common mode noise.

author: bdunham7
author_rank: Super Contributor
timestamp: March 20, 2022, 02:05:25 am
content: I'm not sure what 'double Faraday shielding' would look like on a mains transformer, but the if you want low capacitive coupling and low common mode noise you might look at R-core transformers.https://www.ebay.com/itm/222539735477

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 20, 2022, 04:06:27 am
content: Most likely you'll have to custom engineer a solution.

author: jonpaul
author_rank: Super Contributor
timestamp: March 20, 2022, 08:43:04 am
content: Hello: Ebay Chinese lot NOT shieled but has external shading band to reduce mains H filed radiation.Torids and R type are worst on isolation C due to geometry.Check the stock transformer houses like CoilCraft, Signal Transformer, Renco in USA for a SINGLE shielded (Faraday Shield) NOT "double shielded"Only costly instruments like seismographs need double or triple faraday shields.In HiFi it makes no difference and the CM noise burden is not great and the design of the audio ckt should have good PSRR and CMRRSee the excellent app notes of the late and great Deane JENSENhttps://www.jensen-transformers.com/application-notes/Bon chanceJon

author: ezalys
author_rank: Frequent Contributor
timestamp: March 20, 2022, 02:28:29 pm
content: I've managed to find plenty of split bobbin transformers without faraday shields, and plenty of toroidal transformers with faraday shields, but no split bobbin transformers with faraday shields! Super frustrating.

author: jonpaul
author_rank: Super Contributor
timestamp: March 20, 2022, 05:40:17 pm
content: Hello again ezalysReason for the availability is little market for faraday shield in commodity split bobbin transformers.Can you precice your exact application, give a schema or block, to better understand the requirement for Faraday shield single or double?Since the chassis to line and secondary stray C is ~> 10 pF the shield is not effective in most situations.Very sensitive instruments may benefit but doubt if any difference in hifi, ADC, DAC, consumer audio stuffJon

author: djerickson
author_rank: Regular Contributor
timestamp: May 26, 2022, 02:05:59 pm
content: I'm with ezalys 100%. Virtually every high-end, isolated instrument uses a multiply (dual or triple) shielded power transformer to reduce AC leakage currents. I wonder about high-end audio equipment. If you design your own transformers and have them built by a transformer manufacturer, getting shields is no big deal. But no off-the shelf transformers have quality shielding. This leaves us DIY types hanging.I'd love to see some papers, articles, web sites, videos, etc. on how to fabricate AC and/or switching shielded transformers.I use a medical-grade, shielded toroid on my DIY-SMU project and the AC leakage currents are about 10-20uA. Not great.Davehttp://www.djerickson.com/diy-smu