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Old 17th June 2004, 08:29 PM   #1
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Default total newbie: transformer coupled digital out

Hello!
I'm new at this. I'm modifying my cheap Sony DVDP, used as transport->Monarchy's DIP upsampler->M-Audio moded superDAC.

I've been told that putting transformers on digital in/outs makes wonders. I've got two 1:1 mini-thoroids for this. The Sony's PCB seem very light to re-solder (?).

Any advices about which is the best way to implement this are welcome. Also if someone could post a simple wiring diagram I'll be indebted for life.

Thanks.
Mauricio.

PS: I also consider a thoroidal choke for PS.
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Old 24th June 2004, 02:09 AM   #2
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Never mind.
I did it already. It was easier than I thought.
For those interested: it sounds very clean and detailed. I used cheap RCA and slim wire (silver/copper). I blame those for a "cold" presentation, without much midrange-upperbass.
I'll upgrade connector/wire.

Those who are modding transports should try Tx at output.

Mauricio
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Old 24th June 2004, 05:11 AM   #3
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Default Wonders.....?

Well, it depends.....

They provide galvanic isolation, which helps.

But.....it is hard to get the output impedance right......especially if you are unable to build a zobel network for the transformer.

Most transformers sold for that purpose are inadequate.

Simple wiring diagram.......well, yes, I could draw one for you, but how it implemented is much more important. And that can not be easily drawn.

But a hint......

The impedance of the output has to match the impedance of both the receiver and the cable.

The impecance of a RCA jack is around 30+ ohms, which is too far off to yield excellent results. Yes, it will work, but you notice that you observed tonal qualities that you did not like.

Jocko
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Old 24th June 2004, 11:43 AM   #4
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Thanks Jocko.

I've been told that adding a second transformer at receiver's end (in this case Monarchy's DIP upsampler input) will bring better results, perhaps by attenuating this impedance mismatch?

Mauricio
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Old 24th June 2004, 02:38 PM   #5
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Default I use one at both ends......

But I think that I can safely say that it will not automatically improve impedance match. In fact, it will probably make it worse. Adding transformers can be tricky, even with good ones.

A now retired member does not believe in using them at the receive end. But if he were here, I am sure that he would agree on how difficult it is to find the right transformer for this application. A lot of what is written about them is incorrect, as it is mainly marketing nonsense.

But in brief.......

You want a transformer that has tight coupling. The nonsense that it has to be loose coupling to reduce the effects of noise is just that: noise and nonsense.

A transformer like that will have very high leakage inductance, and that leads to a "signature" on a TDR (the type of machine guys like me use to evaluate this stuff) that is difficult to eliminate. Which means that the impedance mismatch will be high.

Since the cores on any of these transformers.....even the lousy ones.....saturate very easliy, make sure that there is no DC component passing through them.

Jocko
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Old 25th June 2004, 04:46 AM   #6
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Is there a reason this paper, http://www.scientificonversion.com/Aespaper.PDF , recommends the usage of a 2:1 transformer on rx and a 1:2 on tx, instead of 1:1 on both? I guess it is for impedance matching since fig 18 shows their 1:2 transformer and the 300 to 75 ohm change and back?
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Old 25th June 2004, 05:17 AM   #7
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Default I think that I read that one a while ago......

Go ahead......(f it is the one that I am thinking of)......and hate me.

Can't agree with much that they say. I have tried their transformers, and I do not like any of them. Especially the 2:1 varieties. They all leave a nasty "signature" on my TDR, that can not be corrected for.

(The 2:1 ones have a split bobbin construction, and that means low coupling, and high leakage inductance. Yuk!)

Schott used to make the best ones, but they seem to be out of business. Seem is the key word, as I have had heard that they did respond to an e-mail query. About 6 months after it was made............ So who knows??

Right now, I am stuck using some cheap knock-off from Pulse Engineering. Kinda nasty, but I have ways to work around it.

Maybe if I have a week one day, I will try to 'splain it.

Jocko
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Old 11th March 2005, 08:37 PM   #8
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Default Re: I think that I read that one a while ago......

Quote:
Originally posted by Jocko Homo
Right now, I am stuck using some cheap knock-off from Pulse Engineering. Kinda nasty, but I have ways to work around it.

Maybe if I have a week one day, I will try to 'splain it.

Jocko [/B]
Digikey has a couple of transformers from Schott that seem to fit the bill; namely the Schott 22133 and 22160.

Schott 22133
Spec: http://www.schottcorp.com/products/p...s/67129600.PDF
Digikey part no: 470-1006-ND

Schott 22160
Spec: http://www.schottcorp.com/products/p...s/67128990.PDF
Digikey part no: 470-1004-ND

From reading previous posts, I gather that low leakage inductance is key, which suggests the 22160. What would your Zobel impedance network circuit look like with this one, Jocko, i.e. how big should the cap be?
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Old 14th March 2005, 11:53 PM   #9
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Anyone tried North Hills transformers ?

http://www.northhills-sp.com/wb-balun.html

I wonder or they are not better alternative for Scientific Conversion transformers.

I did not try them , are they good?
Regards
Martin
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