The Use of 1:1 Input Transformers in Linestages

[mach1]

In schematics I have often seen 1:1 input transformers employed on the inputs of linestages to provide a degree of galvanic isolation. The use of this topology is generally recommended by its proponents on sonic grounds, and several reasons have been proposed for its employment, including:

• ground loop hum rejection
• the isolation conferred on a multi-source system with multiple grounds
• common mode rejection in a noisy electromagnetic environment
• the inherent bandwidth limiting associated with transformer coupling

My question is: if you don’t have ground loop issues, employ a multi-source system, live in a noisy electromagnetic environment or require bandwidth limiting are there any sonic advantages conferred by this topology ?

My gut feeling has always been that adding extra devices to the signal chain can only detract from the overall sound, and that there would have to be a considerable influence from one or more of the factors listed above to justify their use. Opinions please

[SY]

It would probably confer minimal advantage in that situation. But, like me, you might be surprised at how not-quiet your quiet environment is, especially with the advent of CFL lighting.

[EC8010]

One of the worst offenders for mains noise near audio equipment is ... ... audio equipment. It's all those capacitor input power supplies and saturating mains transformers. And you'd be amazed how difficult it is to get an active crossover system free of buzz. Input transformers can really help.

And here's the current waveform for a 9W compact fluorescent lamp...