Transformers: Auto- vs. Isolating

Excellent response Gs. I would only add that there are vast differences in quality between various isolation transformers. As a general rule, "old school" heavy iron transformers work better than toroidals for this purpose. With that in mind though, some "iron core" transformers are much better than others at isolation due to the way that they are wound and internal capacitance. The lower the internal capacitance, the less coupling / better isolation. Besides that, you want to look for transformers with the biggest cores, as this reduces the effects of saturation and hysterisis distortion.

I went overkill and have the dedicated AC system isolated at the A/V breaker box and then isolated again at component level as needed. I did this using smaller individual iso transformers near the gear. This keeps the AC from other parts of the house and the outside lines from feeding into my audio & video systems and the secondary transformers at component level keep the AC noise generated within the components from flowing back into the system and polluting other components on the same line. As such, they are filtered from both inside and outside the system.

I am currently working on a similar system for my Dad. Luckily, he just has one combo 2 channel / HT system : ) Sean
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PS... Yes, i am finally beginning to realize that i am insane.

Any type of power conditioner or treatment can make an amp sound "slower" by limiting the amount of current available to the device as it is needed. In order to avoid this, select a device that is capable of providing at least 30% - 60% more power at any given time than what the device would draw under full load. As such, if you had an amp that is capable of drawing 8 amps continuous, you would want a device that could supply at least 12 - 15 amps continuous. Since ratings from manufacturers are "fudged" so many times, the more headroom that you can provide in terms of current capacity on the "filtering device", the less likely it is to impact the "apparent speed" of the device connected to it. Too many people try to draw too hard on a steady state basis from various filters or transformers and the distortion that they produce in such cases is passed on into the audio system. By keeping the load on the transformer or filter well below capacity at any given time, those distortions and current limiting are removed from the picture or at least drastically reduced. Sean
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Dmitry: Those are not isolation transformers. They are voltage converters and there is a BIG difference. For one thing a "decent" 1.5KVA isolation transformer will weigh at least ( at the bare minimum ) 30 lbs by itself. I'm talking about just a transformer with no case or chassis weight added. The more "plates" in a transformer, the more it will weigh and the less likely it is to saturate under heavy loads. As a case in point, the 3.0 KVA transformers that i'm using weigh over 100 lbs apiece. This is bigger / heavier than some 5.0 KVA units that i've seen.

While there is more to finding a good isolation transformer than just sheer weight, it is a good starting point. The other major factor would be the internal capacitance rating ( a lower number is better like .00X ) and that of the rate of attenuation ( lower is better here too with -126 being better than -80 etc... ).

What are you trying to do and what country are you located in ? If outside of the USA, what voltage and frequency does your AC system run on ? Sean
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