Hello everybody! I'm trying to build a passive DI box, but I need to clear some things up first. So here's my plan: guitar line goes into a step-down transformer, into a mic pre. Simple enough? But what input impedance do I need on the transformer? I know for an op amp, or a transistor, I would want the highest impedance possible, as these don't need the voltage transfer, so much as current. But what about a Xformer? Wouldn't I want it to match the guitar so I could get the maximum voltage transfer? But I've seen a lot of people recommend a 200K input impedance, which is way up there! Wouldn't this give me a thin, trebly sound? But if I match them, I'll lose half my guitar signal! I already ordered the transformer when I thought I had to match them, it's 65K. But this can be adjusted, sort of, by running a pot in series or parallel with it to change what the resistance looks like to the guitar. But I saw a list of different pickup specs and their impedances at various frequencies change drastically! Like 8K for low frequencies, 80K for high frequencies! So if I do match them, or not, which of these frequencies do I consider the "guitar impedance? As you can see, I'm pretty confused, and the time has come to ask for some guidance. So could somebody please tell me what the input impedance should really be on a DI, and why?
Thanks!!
A good place to find good examples is Jensen site
http://www.jensen-transformers.com/as/as013.pdf
http://www.jensen-transformers.com/as/as066.pdf
http://www.jensen-transformers.com/as/as097.pdf
The,by looking at the specs of the tranformers, you will learn a lot.
More good reading:
http://psbg.emusician.com/ar/emusic_going_direct/
Gilles