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Old 11th August 2010, 07:30 PM   #11
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Sure they are, JT 11-DMCF or DMPC. The 2nd is PCB mount, one of their best units. $80
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Old 12th August 2010, 07:36 AM   #12
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It seems a good polivalent transfo, very suitable for experimenting and using in different configurations... claims to try mantaining input impedance as low as possible, for this application it might be seven times higher than the nominal 680 Ohms, so the result is not predecible unless tested.

Link to Jensen JT 11-DMxx datasheet
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Old 12th August 2010, 11:13 AM   #13
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You might want to download the Jensen article by Bill Whitlock about audio transformers and read it a few times. It will help you wade through the choices and give you a better perspective.

The dac chip will never see a 680ohm load until you get below the threshhold where inductance affects the low freq.cutoff more than the reflected impedance does.

The chip probably has a source impedance around 500 ohms, going by the general rule of the 10/1 ratio of rated load to source. The trafo will just reflect the secondary load until you approach the area where the trafo inductance dominates the perceived chip load, and that will be in the subsonic range below 20hz. When the source impedance equals the perceived load impedance you have a 3db voltage loss, and as the load impedance decreases at lower frequencies the losses become much greater. That is why you want a lot of inductance, the more you have, the lower the low freq cutoff will be.

As long as you are transferring voltage, not power, the lower the source, the better. Power transfer involves impedance matching, but that's not what we are doing here.
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Old 13th August 2010, 12:33 PM   #14
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Quote:
Originally Posted by Bill Fuss View Post
As long as you are transferring voltage, not power, the lower the source, the better. Power transfer involves impedance matching, but that's not what we are doing here.
Bill, you're THE master

Some time ago I read about speaker impedances and why they might match with amplifier. Few days ago I read about line level and they told that line input and output impedances might be far from being similar. It drove me confused because it was absolutely opposite to what said about speakers and amplifiers.

Thanks to your explanation I know that when dealing with speakers (power) impedances must match and why they don't do it when transfering voltage.
It could seem a fool thing for an electronics engineer, but I am only a computer scientist trying to self-learn electronics, this kind of help is really very appreciated.
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Old 13th August 2010, 02:01 PM   #15
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Thank You both

Gary, for asking the question

Bill, for answering it, and leading me to the Jensen/Whitlock chapter

I'm soon to buy transformers for this purpose (a different dac). Bud Purvine of O/Netics has provided useful recommendations
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Old 13th August 2010, 02:44 PM   #16
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Thanks Ed for participating on this thread. I hope we could collaborate since it seems both you and me are pursuing the same -or very similar- target. Just one question Ed: different DAC but sigma/delta output, or different DAC with voltage/current output?

I'm sure the ideas from this thread will be very useful for the tweaking community. Thanks all.

I add the link to the article about transfos pointed by Bill: Audio Transformers by Bill Whitlock

Last edited by GaryKrant; 13th August 2010 at 02:49 PM.
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Old 14th August 2010, 11:56 AM   #17
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Quote:
Originally Posted by GaryKrant View Post
Bill, you're THE master

Some time ago I read about speaker impedances and why they might match with amplifier. Few days ago I read about line level and they told that line input and output impedances might be far from being similar. It drove me confused because it was absolutely opposite to what said about speakers and amplifiers.

Thanks to your explanation I know that when dealing with speakers (power) impedances must match and why they don't do it when transfering voltage.
It could seem a fool thing for an electronics engineer, but I am only a computer scientist trying to self-learn electronics, this kind of help is really very appreciated.
I'm sure no master, by any stretch. A guy like Bud Purvine IS a master. I'm not exactly technically accurate in my ramblings, just trying to be helpful.
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Old 14th August 2010, 01:48 PM   #18
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Quote:
Gary asked the question:
...different DAC but sigma/delta output, or different DAC with voltage/current output?
...and it was as if I had run into the door jamb. I think the latter...

You illuminate another area I don't know enough about. When I am confronted by my own lack of knowledge I retreat to (or go find) the references to help me along the way.

I try to improve the singular elements of my system. In this case the cd player/dac. I have the shigaclone, I need the dac.

Last edited by Ed LaFontaine; 14th August 2010 at 01:52 PM.
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Old 15th August 2010, 05:23 PM   #19
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Ok, you mean DAC as a device while I mean DAC as a substage on a CD player. Have you considered any approach? I'm not very experienced in that matter but I remember Lukas Ficus (from Lampizator) combining a Wolfson test board with a tubed output and saying it was the best DAC he had heard is his life.

The link: WolfsonWM8742DAC

Anyway I'm interested in building a decent DAC (as device, not as player stage) since I've decided moving, after finishing this project, from CD players / transports to a WiFi or memory card based transport.
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Old 15th August 2010, 07:12 PM   #20
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You might find this interesting. Decware is now selling their version of the Ebay Chinese upsampling CS4398 dac board installed in a cheap case, for $875. I have had 2 of these boards for quite some time using output trafos with both. They cost $90 on Ebay and they are quite well built and sound excellent with trafos.
Decware has a lot of nerve, but proves a lot of the Chinese stuff is quite good. I have one built into a Redbook player and feed the other with an SB3.
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