Hi Gurus,
I am working on a bit of a left field project. I have the need to interface the audio to and from a piece of software on a laptop to a radio transceiver.
Now it's a given that the computer uses a switchmode power supply and the radio a linear power supply. this means there is a rather good chance of quite varied ground potentials between the two devices.
To protect both I ideally need to isolate the two and the simplest way (I thought) is to put a couple of 1:1 transformers in the audio circuits. A bit like a passive DI without the impedance change. So this was done. Strangely this simple thing has been very difficult to get working. Faulty components and very low signals have plagued the project. To add a further complication I used to borrow test kit from work to investigate this sort of thing (CRO, signal generator, spectrum analyser, etc) but where I work these days doesn't use that sort of gear.
Anyhoo, after a few frustrating days of dicking around with a very simple circuit and getting stymied in every direction I was about to give up when I spied my little Behringer 3 channel mixer. I cobbled some leads up and bingo audio now flows in both directions and radio happily sends its messages out into the ether, well almost happily. The little mixer id quite susceptible to RF and chucks a wobbly every so often.
This situation has me wondering if a mixer would generally have galvanic isolation as a part of its design. I do wonder because of the existence of DI's.
Further, what types of USB interfaces are there for use with DAW's and the like?
Using the simple transformer isolation in front of the audio I/O of a simpler USB interface may overcome the low signal level issues I am facing.
The RF issues are something else I need to sort but getting a reliable interface is the first step.
In short, what USB interfaces are there for use with DAW's?
And what isolation would I expect to find in a little USB capable mixer, if any?
Cheers