DIY Passive DI box transformer advice

[ojc123]

I don't pretend to be an electronics wiz although I've learned a few tricks over the years.

 

My student technicians (13-14 years old) are always looking out for new challenges and things to do. We recently repaired a simple DI box and they asked could they make one from scratch. A bit of Googling and other research suggests it's reasonably straightforward so we're planning to have a go purely for educational purposes not, at least in the first instance, to try make a cheap version.

 

I understand that we need a transformer. I also understand that good quality is necessary for proper use and I'm prepared to get some decent and some cheap transformers so we can compare and contrast their behaviour.

 

So far I think this might be ok for a decent one. Am I right?

 

If so, what I need to know is what specification of transformer to search for so we get the right type of less well manufactured transformer.

 

Thanks in advance.

 

PS If, in true Blue Room fashion, someone tells me that it's better to buy a super-duper-go-faster-zippity-do-da £1000 active DI box then they've entirely missed the point and will be ignored. Thanks again.

[DrV]

You might find it more informative if you try using something TOTALLY unsuitable like a mains transformer. The difference between a cheap and expensive 'suitable' part might be a bit subtle. Just a thought...

[ojc123]

You might find it more informative if you try using something TOTALLY unsuitable like a mains transformer. The difference between a cheap and expensive 'suitable' part might be a bit subtle. Just a thought...

Thanks for the suggestion. We may try a variety of unsuitable transformers as well.

What I need to know is what do I search for to get a suitable cheap transformer.

[timsabre]

Try "1:1 transformer" as a search term

[ojc123]

Try "1:1 transformer" as a search term

This is where the problem started. I'm getting 1:10, 1:12 and 1:1 from different sources.

The diagrams are effectively the same simple circuit. I assume that 1:10 would step down a lively line input for something like a synth but a 1:1 would not do that?

 

This one I linked to before was a 1:3:10.

[timsabre]

Um you might be right - to match the impedance correctly a 1:1 wouldn't be right - 1:10 ish is probably correct

The passive DI's I've seen use resistor dividers to adjust the signal level.

 

You could always buy a cheap passive DI to dismantle and analyse as part of the experiment...

[david.elsbury]

I've used the neutrik nte-1 1:1 transformers for projects and installs before, perfectly acceptable. I think because they ar so physically small they don't have a great bass response but that wasn't an issue for me

[Dave m]

http://www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_VARIOUS_7.html

More for specs than recommendation as they are possibly above buget

[ojc123]

You could always buy a cheap passive DI to dismantle and analyse as part of the experiment...

We have a broken one which we haven't repaired yet so we'll perhaps do that.

[Jivemaster]

RS Stock No. 123-7198 is a DI transformer by an OK brand at a fair price and the school may even have an RS account and buy one for you.

 

Other transformers from searching RS for Audio transformer and selecting brand OEP may offer other ideas.

[themadhippy]

Make em wind there own transformer

[alistermorton]

That's not a daft idea.

[ojc123]

Make em wind there own transformer

Might just do that too!

 

RS Stock No. 123-7198 is a DI transformer by an OK brand at a fair price and the school may even have an RS account and buy one for you.

Thanks. We do have an RS account. It's knowing what to search for is my problem. I'm on my way now.

[haymere]

Interested in this topic, because I am in the same place. Orchid active DI’s are brilliant but I am after some Passives & as I wire Electronic Control panels for a living this wouldn’t be hard. I would be interested if you ever took any photos of your results or noted any of your findings

[Brian]

Many years ago I built some clones of the EMO passive DI boxes. I should still have them somewhere in the store, I'll take a look and see what I can find.