Some basics:

a) Isolation transformers are designed to protect users under some conditions, and *certain* types of equipment under *VERY* limited conditions. Those latter applications are primarily under hospital and research conditions where an isolated ground is not enough. Generally, RF-shielded rooms use isolation transformers in their power-supplies, for example. But, no equipment protects against deliberate stupidity or carelessness. If one inserts oneself into the circuit, one will be stung.

b) Voltage adjustment transformers tend to be as inexpensive as possible per-watt. A true isolation transformer would have very nearly twice as much conductor in it as a simple auto-transformer. Not t mention more core material as well - I am careful not to use 'copper' or 'iron', as very cheap devices will use neither.

c) Any unnecessary equipment adds a degree of unnecessary complexity - and with it an opportunity for error. I have a 110/220 step-up/down transformer purchased in Saudi Arabia with no markings at all. It came with a Euro/US adaptor that could plug into either side. So, I engraved "High Side" and "Low Side" on. Imagine me going the 'wrong way' in actual use. Not so bad going from 110 to 55 volts. But 220 - 440 V, not so good either.

If you need to step up/down, check the equipment. A surprising amount of vintage audio equipment has multi-tap primary transformers that might require only a simple change in wiring, and a surprising amount of modern consumer electronics have smart supplies that do it all automatically. Otherwise, a brand-name surge protector (with a downline equipment warranty) will be your best option to protect your equipment.

Peter Wieck
Melrose Park, PA