Instrument (DI) feeding input transformer on a micpre

[dramadisease]

So I've been searching for an hour or so and i'm coming up short with trying to figure out the best way to do DI that feeds input transformer on a mic pre to use as one big DI. A while back Fred Forsell had a fet based circuit that Dan Kennedy designed that i think is what i'm looking for but it doesn't seem to be there anymore.

Has anyone done any expeirments on this topic? I know theres the JLM DI board out there, but i'm looking for a discrete option.

ideas?

thanks!
-bryan

 

[Jim50hertz]

http://web.telia.com/~u31617586/

 

[BradAvenson]

http://www.groupdiy.com/index.php?topic=14150&highlight=

I think this thread has what you are looking for: A clever circuit that dan put together to switch the DI to the input transformer when you plug into the jack.

 

[dramadisease]

yeah that was exactly what I wanted..

besides these 3 examples (Hansen, GR, Jensen) is there any other examples out there of this type of circuit?

Looks like its basically a gain buffer to low impedance driver, but GR grounds one side of the transformer and the Jensen circuit does a balancing conversion (as does the JLM DI)

I'm just trying to come up with my own way of doing the same thing really. Love the TRS jack used to switch the relay, very elegant.

-b

 

[BradAvenson]

If you are going to put this in the mic preamp box, balanced audio for 2-3 inches is a bit of an overkill. If you are making and external box then balanced is the way to go.

You can use any high impedance circuit for the DI part. Mainly I was pointing out the switching bit.

 

[dramadisease]

I really do like the switching in that circuit, I have to admit...

My aim in this is to make a utilitarian circuit that i can plop into all the rack jobs i have coming up, to allow a DI use with the racked up module.

example -> gotta do 2 calrec modules and 2 V676 next week - i want to add DI to them, but I don't want to be invasive to the module, so a DI that feeds the input transformer / input section seems to be the best method, as it would work on a variety of circuits.

Would that switching circuit still work ok with a transformerless module? (in other words, would grounding one side of a transformerless circuit damage it in any way?) I would think most units like that would have short protection, but i'm wondering about a prolonged short.

thanks brad!
-bryan

 

[mikep]

[quote author="dramadisease"]I really do like the switching in that circuit, I have to admit...[/quote]

yup. I came up with that same exact sensing/switching circuit independantly. what better proof-of-concept to see it in one of Dan's designs. I guess Im doing at least something right.

mike