Difference Between A DI w/ Ground Lift and an Isolation Transformer

[wheresgrant3]

I'm a keyboard player in a cover band and my setup is pretty self contained. 3-4 synths running into a stereo line mixer into an active DI (Samson). For most rooms the DI is suitable, and the ground lift seem to lift the 'hum' from my gear as it's delivered to the FOH mixer. However there are rare occasions where I can't remove the hum. I invested in a passive stereo isolation transformer (ART)and the results have been great. What I find is that some rooms the Active DI works better, and others the IT works better.

 

My question is what's the basic difference?

[dboomer]

With a transformer in place you break the direct electrical connection. You go from electricity to magnetic then back to electric. Active DI may or may not have transformers (usually not). They are usually just impedance correcting devices that send out a balanced signal in which case they directly connect the two pieces. The transformer can protect against shock hazards. As to which sounds best it could go either way.

[agedhorse]

A passive DI would include an isolation transformer.

 

A DI typically has a 6:1 or higher step-down ratio going from high to low impedance. It will also provide isolation.

 

An "isolation" transformer generally has a 1:1 ratio, and may have additional electrostatic shields internal to the transformer. They are available in line or mic level.

 

An active DI may or may not have a transformer, and if operated on phantom power may not isolate as well from ground loops.