DI'ing a 100V line

[timd]

I might need to get audio back out of a 100V line system, back down to line level. Canford make a box that does it, which looks a lot like a passive DI with a variable attenuator. Is it that simple? I've got some decent passive DIs with attenuation of 40dB (fag packet calculation says 100V attenuated 40dB comes out 1V, so line-ish level) and ground lift - is that a possible and safe approach? It's also worth noting that the two systems will be on separate mains supplies, does that make a DI box an inappropriate solution in this case, regardless of DI boxes?

[MarkPAman]

I might be tempted to feed my DI box from a 100V line transformer, like this one, for instance

[DrV]

I might need to get audio back out of a 100V line system, back down to line level. Canford make a box that does it, which looks a lot like a passive DI with a variable attenuator. Is it that simple? I've got some decent passive DIs with attenuation of 40dB (fag packet calculation says 100V attenuated 40dB comes out 1V, so line-ish level) and ground lift - is that a possible and safe approach? It's also worth noting that the two systems will be on separate mains supplies, does that make a DI box an inappropriate solution in this case, regardless of DI boxes?

 

I would do it by putting a 100v line transformer first and using the output of that to provide something a bit more user friendly and then use a resistive potential divider to get the level you need. This would have the advantage of being fully isolated - typically on a 100v system you would not know which was the hot and which was the ground wire.

 

Dave

 

E2A Mark got there first!

[timsabre]

If you use a transformer di with earth lift, padded down, that is not really any different to using a 100v transformer. It doesn't matter which is hot or ground on the 100v side as the di completely isolates it.

[MarkPAman]

True.

 

But, it's probably not be a very good idea to have 100V on a jack plug, which could easily get shorted out, or plugged into the wrong hole.

 

Also, I'm not convinced that 40dB is a big enough drop. I guess it all depends on what it is that you're plugging into and how hard the 100V system is being driven.

[Chris Beesley]

Monacor offer a box called the PATL100 which gives you a balanced line from 100V. Its a touch pricey though.