isolation transformer vs line conditioner

The transformers I was talking about were used in power converter applications - granted they were mostly nonlinear applications such as resonant topologies and voltage source inverters but it is still clear to see what impact is on the the waveform. Transformer design is very complex - much more so that I made it seem in my over-simplified general comment above. I agree in some instances, you can get the input very close to the output but in general, the B-H curve of a transformer is totally nonlinear. There are some very linear cores but they are more often than not only inductors - similar to McIntosh's autoformer where the action is self-inductive. My comment didn't apply to that but rather complete transformers with a ferrite core, primary, and secondary. In this case, you are at the mercy of the B-H characteristics which are far from linear unless you operate in a very specific range but that never happens when you are talking AC voltage of course. Many of the commercial isolation transformers are undersized and so you run too close to the saturation region where the flux density starts to level off (i.e., nonlinear). Oversizing the transformer costs lots of $$$ and we all know that engineers are forced by the bean counters to keep cost in check - this means you don't add any more core than is absolutely necessary. If the end result is for electrical equipment in a medical lab, the core WILL NOT BE OPERATING LINEARLY because it will be made as small, light, and cheap as possible. It will be just fine for electrical equipment but not necessarily for human ears. Some audiophile companies may do it right but again, I would check it in the lab before betting my life on it.

Having said this, some people may actually like a nonlinear sound eventhough it is totally inaccurate from a strict electrical sense. One more example of "if you like it, keep it." All I am saying is you need to be careful when using a transformer. It isn't a simple thing.

I looked for the waveforms I was talking about but couldn't locate them off hand (we may not have even saved them). There are many examples online about it if you are interested. I will look for a good example and paste the link. The problem we were having was that the slope of the B-H curve changes depending on the direction of the applied voltage becuse that little bit of loss results in "fattening" of the curve which makes the slope different no matter how linear you make it. This is a problem.

Finally, be sure you realize that an autotransformer is NOT the same as a transformer. The two words are not interchangeable. Arthur

An autoformer is simply an impedance matching device, whereas a transformer can be both a power transfer device and / or an impedance matching device. Then again, anything that alters impedance WILL alter power transfer to some extent, so one can generalize that they have similar purposes regardless of how they are used or designed. Obviously, one needs to choose a product suitable for their specific needs.

As to the core sizes of iso's, i've commented on this extensively in the past and even in this thread. Hence my recommendation to utilize transformers that are rated well above and beyond the necessary amount of power consumed. Larger cores will also help to stabilize the magnetic flux, increasing the efficiency and reducing non-linearities in the power transfer curve. They will also lower self-induced noise prior to saturation and maintain a lower impedance, allowing for better transient response. All of this adds up to increased linearities and better performance for the end user.

Out of curiosity, were the iso's that you were using / performing the testing on toroidal or "iron core" based? This makes a HUGE difference for multiple reasons. I've also mentioned this many times in past threads.

Outside of that, designing a transformer for one specific purpose is much easier than taking a "universal" product and making it work for your specific application. The fact that the units that you were studying were used in non-linear applications i.e. voltage inverters ( very "dirty" to start with in most designs ) etc.. may have tainted your opinions of what can be done and is possible in other areas of transformer operation. Given that we are looking for maximum linear power transfer at one specific frequency with attenuation increasing as frequency rises, the transfer function of an iso transformer IS "non-linear" by very design. The key here is to find one that was designed for this very specific purpose with suitable traits, hence my recommendations of specific brands and styles while avoiding those that we know are less than optimal. Sean
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We are senior electrical engineering PhD students. We know the difference between dirty and clean waveforms.

The cores were custom nickel and molybdenum alloy EE cores which are already much better than most commercial-grade transformers. Toroids are terrible for isolation transformers and so aren't used for that purpose.

Keep in mind too that with any power conditioning, the impact on the sound is largely dependant on the quality of the components' power supplies. Arthur

"Toroids are terrible for isolation transformers and so aren't used for that purpose."

The BPT products use toroids.

"We are senior electrical engineering PhD students. We know the difference between dirty and clean waveforms."

I would hope so, but then again, that's why i asked. The mass majority of inverters on the market aren't typically known for being "clean" sources of power. Hence, a distorted waveform in would equal a distorted waveform out. That is, IF the transformer was actually "linear" in operation. I had no idea where you were coming from or what you were basing your comments on, hence the need for clarification.

"The cores were custom nickel and molybdenum alloy EE cores which are already much better than most commercial-grade transformers. Toroids are terrible for isolation transformers and so aren't used for that purpose."

There are TONS of isolation transformers on the market that are of a toroidal design, but thanks for confirming what i've been saying for several years now. Many of the various "computer grade" or "commercial grade" iso's that come in cute little cabinets are toroidal. In fact, most all newer gear uses a toroidal based power supply because it is FAR cheaper to make, FAR cheaper to ship ( less weight ), FAR cheaper to house ( less weight means less rugged chassis ), etc... Only problem is, they allow GOBS more line noise into the componentry and typically saturate much faster than a well built "iron core" transformer.

The fact that audiophiles have been led to believe that toroidals are "superior" is strictly the marketing department pumping out snake oil by the gallons. The only things that toroidals are superior at is generating a profit margin and they "may" be better at reducing stray magnetic fields. This will depend on the construction of the "old school" iron core transformer though.

"Keep in mind too that with any power conditioning, the impact on the sound is largely dependant on the quality of the components' power supplies."

I agree as stated in the above response. On top of that, most power supplies are lacking, hence the great variance in power cord effectiveness from component to component. Some components make use of much better power supply design and parts selection and others make use of parts that "get the job done". There's a big difference in performance levels between the two. Sean
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