Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Re: DI/O Jensen transformer mod...calling GaryB

Posted by Steve Eddy on March 13, 2002 at 18:48:47

In Reply to: Re: DI/O Jensen transformer mod...calling GaryB posted by Gary B on March 13, 2002 at 16:51:05:

I'd like to thank Steve Eddy and all the others for the interesting discussion.

Pleasure's mine. I've been using transformers for years and it's nice to see them starting to overcome the old stigma.

The line output transformers that Steve recommends are very good but may not be appropriate for this application. They are meant to be driven by a low source impedance which isn't really available in this case.

What are they actually being driven by in the case of the DI/O? If it's in the range of several hundred ohms or less, you'll be ok.

The impedance the line output transformers present back to the DAC chip is about 680 ohms according to the data sheets, while the DAC chip wants to see a minimum 1K ohm load.

That's because the testing was done for the worst case scenario driving a 600 ohm load impedance. The load it presents to the source depends on the load the transformer is driving. So if your preamp's input impedance is say, 10,000 ohms, the 11-DMCF will present a load to the DI/O of 10,080 ohms. In other words, whatever the load impedance is plus the 80 ohms total of primary and secondary DC resistance.

Transformers can be a bit confusing because they don't have an intrinsic impedance save for the DC resistances of their primary and secondary windings. What transformers do is reflect impedances based on the square of their turns ratio. Which for 1:1 output transformers is simply 1. So its output impedance will be the output impedance of the source plus 80 ohms and the input impedance it presents to the source will be the load impedance it's driving plus 80 ohms.

Additionally, they are physically large and don't fit inside the DI/O.

Yup. They are that alright. :)

The output of the DI/O is differential with no DC component, so the concerns over core saturation aren't really relevant.

Good. They're not using any coupling caps on the output are they?

Net: for this application, the Jensen JT-11P-1 is a good compromise for what I was trying to achieve. I've done this mod to my own DAC and in a friends DAC and it works very well.

Coolness. And of course that's all that counts. And please don't think that I was trying to imply that your particular solution was somehow inferior. Just that some seem to be a bit more concerned with objective critiera than others and just wanted to expand a bit on the issues involved so that people could make up their own minds which route to take depending on what their goals were.

se

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