Sorry for the late reply, didn’t see the notification.
The decisions on the various transformers goes something like this:
Will you be installing a dedicated circuit? If yes, you can get the transformer that is hard wired into the circuit. You simply have to calculate your power requirements and buy the right size. Then from the fuse board a wire goes into one side of the transformer (primary) and out (secondary) to your line of sockets. A radial circuit this will be and you can have as many sockets as you’d like.
If That is impractical you can add it onto your ring main and create a spur and then have you radial sockets coming off the secondary as described above.
These transformers work by removing the earth link, in effect making it an earth free circuit. It gets around the danger of not having earthing by using and rcd. How that works is not something I can explain on my iPad.
The separation (or isolation, hence the term isolation transformer) allows our equipment to be at equi (equal) potential. We also do this with analogue interconnects through balanced xlr cables for example.
If you are just going to be plugging a few things in, airlink also makes the transformer with sockets in it. Same principle as above but a simplified plug and play solution.
The other decisions are if you want the supply filtered. The idea is good, but the more you filter the more it impacts the sound. It is a compromise. They are designed for situations where the supply is particularly dirty. It is more prevalent in America and Australia, but in U.K. we are fortunate to have a decent supply. If you lived on an estate next to an industrial estate with lots of high loads and plenty of heavy industrial machinery, then filters can help.
It’s very much the same as TV (and audio) processing. We want DSP turned off as much as possible to get the purest sound/picture but in some cases, like dodgy SD cable broadcasts we have to turn on some processing to improve the overal picture.
Other factors to consider is voltage stepping. Again in US in particular the voltage can fluctuate. So you can have transformers that step-up or step-down the voltage. Again it’s not something that really happens in U.K. Equipment is designed to work in a voltage range and as long as your supply is in that range you’ll be fine. Because of European harmonisation our voltage is 230V.
The one thing you do want it to have is surge protection. This protects your equipment if there is lightning or a power cut and when it gets turned back on there can be some serious surges. If you imagine turning your entire house on at the same time, there is a big load all at once. Well multiply that 1000 times when the supply authority turn their transformers back on for every house and business on the same supply as you and it’s clear to see you don’t want that hitting your sensitive equipment.
So tell me what sort of installation you want I can can help advise on the right transformer for you.
At the end of the day you are trying to create a clean and stable circuit. Stuff that have large inductive loads like household appliances (fridges in particular) will affect your circuit. That is why you want your sound equipment circuit to be separate. Ultimately how you achieve that is up to the individual. For me, I created a new circuit and hardwired in an isolation transformer.