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Sunday, October 15, 2017

Isolation transformer effectiveness

Many had asked us, you have so many types of isolation transformers, which should I choose? 

Instead of repeating ourselves again and again (not that we're not willing to, but just to save everyone, and our time), here goes the effectiveness rating, from our perspective, from low (bad) to high (good), with some comments:
  1. Toroid isolation transformer (for HT, audio OK too but not warm and clean as C or EI)
    1. Up to 3.5KVA for highest grade toroid core (other grades with higher KVA are available but not recommended)
    2. >3.5KVA, go for parallel toroid for lower impedance 
  2. C core isolation transformer (for audio and HT) 
    1. Up to 1KVA (bigger size, can be custom made, up to 3KVA)
  3. EI isolation transformer (for audio and HT)
    1. Up to 3KVA
  4. C core ultra isolation transformer (for audio and HT)
    1. Up to 1KVA (bigger size, can be custom made, up to 3KVA)
  5. EI ultra isolation transformer (for audio and HT) 
    1. Up to 3KVA
Some articles about ultra isolation - article 1, article 2

OCC copper magnet wires (Ohno Continuous Cast) transformers are available for #2 to #5. OCC comes with a hefty price tag though. 

Benefits of OCC - lower DCR, better dynamics and clarity. We often use OCC for our output transformers, but for true audiophiles, those that hear a difference with high grade power cords, this is definitely better, and higher ROI compared to using OCC based power cords. 

Options:
* Balance or single ended outputs
* Multiple-taps isolation (explanation below) 
* Potting/frame
* Multiple shielding (electrostatic, primary/secondary, secondary/secondary
* Can be made as power transformers with isolation/ultra-isolation for SS and tube amplifiers

Multitap-isolation? 

What is multitap-isolation? Normal isolation transformers have only 1 single set of outputs, say:

- Primary: 0-240V-G
- Secondary: 120V-0-120V (balanced)

Multitap-isolation is as follow:

- Primary: 0-240V-G
- Secondary 1: 120V-0-120V (balanced, isolated/shielded from 2/3)
- Secondary 2: 120V-0-120V (balanced, isolated/shielded from 1/3)

- Secondary 3: 120V-0-120V (balanced, isolated/shielded from 1/2)

This way, instead of having multiple gears connected to a single secondary, each output is connected to 1 set of secondary to make 3 sets of ISOLATED outputs. This way, the CDP, tube preamp, and DAC (for example), are isolated from one another as they are connected to different secondary windings instead of connected altogether in a normal isolation transformer unit where all the outputs are connected to a SINGLE secondary. 

This is a MUCH better isolation scheme than normal paralleled output on-the-shelf isolation transformer unit. Yet, it is more cost effective than having 3 units of separate isolation transformer, which is the ultimate way one should do it, eventually perhaps.

Go go go, custom made audio!

J&K Audio Design
10/15/2017


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