About the Jensen DIY DI...

[inverseroom]

...can I use a TM018 instead of the Jensen transformer? I'm planning to put some heavily effected geetar directly into my mixer for my little electronic duo, so I don't really care how "guitarey" it sounds...at any rate, I'm not familiar with the technology of transformers, and I happen to have a couple of these TM018's lying around.

[ulriggribbons]

Hey there,

It might be helpful to include a link to the schematic your discussing, and the specs on the transformer (have never heard of the TM018).

Regards

ju

[inverseroom]

OK, cool. TM018 specs (pdf alert!):

http://www.mouser.com/catalog/specsheets/164267.pdf

Jensen DI schem (another pdf):

http://www.jensen-transformers.com/as/as066.pdf

[ulriggribbons]

Next question is what TM018 you have.

The mouser spec sheet has about a dozen part numbers.

You're looking for something that matches the rough characteristics of the JT DBE used in the jensen schematic, which is 200k:1.5k (12:1)

On the spec sheet you posted from mouser above, about the closest match is the 42TM117 50K:1K(8.7:1), which may get you in the ballpark.

The gist of it is you have a high impedence device ( your guitar/bass), and a low impedence input (mic input), so you're looking for a transformer to do the conversion for you

Someone correct my eyes if I've gone astray =)

Regards

ju

[edanderson]

the tm018 as listed on the pdf data sheet is a 10k:10k center-tapped transformer -- not ideal for this application. you could try connecting your guitar to pins 1 (tip) and 3 (sleeve), and pins 4 (pin 2 XLR) and 5 (pin 3 and 1 XLR) to your mixer input. you can skip everything else in the jensen note; i would not expect it to sound "good" but it might actually work fine for your stated purpose. experiment with a 10k pot across pins 4 and 5; if you find a value you like, measure the resistance and replace it with a resistor.

if you want something cheap that will work (but also not sound great), go to radioshack and get part number 274-017 for $15. note that they put the word "pro" in quotes in the description. and hey, you don't even have to build a case.

for a bit more money at $20, you could buy an oep a262a3e transformer (newark order number 06WX2808) which would sound good for a passive DI. takes a while to get here from england tho.

if you ever really want to make a jensen-style di box, you can get a cinemag CM-DBX for less money than the JT-DB; it sounds as good.

also not expensive, but more complicated, would be to build the hamptone JFET circuit (as seen in tapeop magazine!!!), and slap a $12 edcor XSM600/600 on the output.

ed

[ulriggribbons]

ah, I knew I wasn't readin it right =)

I would recommend the last of the above options

http://www.shinybox.com/product_info.php?products_id=37

That's exactly the Hamptone JFET amp block with a 1K pot hanging off the output, driving a 1:1 output transformer.

On the input side, strap a 10M resistor between input and ground. This was recommended by buttachunk over at the group diy board.


Loverly =)

ju

[inverseroom]

I actually have a Hamptone JFET, I built it a few months ago. Believe me, I don't need a DI for my studio anymore! I just wanted to build something into a Hammond box that I could haul along with me on gigs.

I may just buy a plain-jane Rolls DI for this purpose...it doesn't have to sound fantastic, just reasonable.

Now I'm off to find a transformer FAQ...

[ulriggribbons]

A transformer faq.

You'll want to read this. Written by a legend in tranformer info =)

http://www.prodigy-pro.com/forum/viewtopic.php?t=467

Regards

ju