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Saturday, June 25, 2016

Isolation Transformer Bandwidth

How effective is isolation transformer? 

Not all isolation transformers are built the same, and hence the effectiveness of filtering noise varies significantly between design and implementations. It is the bandwidth that counts, or the limitation of the isolation transformer that filters the noise outside of the pass-band.

Benefits of isolation transformers – we have mentioned it several times. We are not going to repeat it here. What we have now is our continuous effort in seeking for perfection in each and every products.
For J&K followers, we believe they have already accustomed to our grading of transformers, from low level to high level. Every step one goes up the ladder, the quality and performance of the product is raised significantly. Do not be-little these grading. The end results – sonic improvements is substantial. Ignorant folks can still go on with their lives using low grade transformers, that’s their lost, your gain (Pun intended! LOL), especially important for those that make tube amplifiers for sale – to gain an edge over others.
Back to isolation transformers, even they have grades in terms of winding and core quality. An ideal isolation transformer is a bandwidth limited passive device. Passive as in it does not have any active circuitries with it. Isolation transformers last long too (almost indefinitely) if properly built and maintained (no accidents too). Bandwidth limited as in it does not pass signal (noises) below and above the pass-band, therefore filtering all those noises / interference / unwanted signals away. 
 Here are the specifications of how good isolation transformer should have:
  • Efficiency ~95%
  • Regulation ~5%
  • Common mode rejection ratio (CMRR) >= 120dB
  • Differential mode rejection ration (DMRR) 1kHz >= 30dB, 200kHz => 45dB
  • Primary – secondary capacitance ~0.006pF
  • Peak attenuation ~30dB 
Our power line should be only filled with 50-60Hz sine wave, which is the base frequency of electricity transmission. Due to various noises being generated by connected equipment on the same power line, as well as radiation from surrounds (radio signals, EMI/RFI, cellphone signals and etc), it is very, very polluted. They come in various forms and are riding on the 50-60Hz line into our audio system. Isolation transformer will effectively filter out all those unwanted noises. 

There are two types of noise - differential and common mode noise on the power line and both can be filtered by balance isolation transformer. Single ended isolation transformer can only filter differential mode noises.

A truly balanced isolation transformer will have 120dB of rejection at 100Hz! Less balance isolation (not fully balance on winding) will not work as good and as effective. 

Putting the numbers with dB might not look significant since dB is not something we work with every day. Let's convert it to gain and see how much noise and spikes attenuation can it actually get! 

40dB of attenuation means the noise is reduced by 100x! 

Hear the Unheard. Hear the Difference.
Only at J&K Audio Design

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