Basics on transformer-coupling dacs ?

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Looking for basic guidelines regarding use of a Transformer in the *output position* of a given DA converter... I'm interested in modding a specific Dac, but I find I don't quite have a grasp of the names of things, the relevant values, etc ..

There are lots of posts about specific implementations, but here are 5 generic questions I hope to get some information about ....

* What information is critical --about the Dac--- in order to specify an appropriate transformer ? Output impedance, voltage, what is the important info to know ?

* This one for beginners, like me -- What, exactly, is the name of this transformer-- Interstage ? Line-level output (preamp out) ? Isolation ? Matching ? I see posts recommending all sorts of different tx types in the output position of typical Dacs; is this a case where the specs tell the tale and the name of the thing can vary ?

* What are the minimum values & info you need to find an appropriate audio transformer in a manufacturer's catalog and have it match the output of your dac ?

* In most cases the pre-existing output cap is removed and the transformer is wired into it's place. Anything non-intuitive about that, any exceptions, or "don'ts" -that apply ?

* Once a transformer is in place, I've seen posts discussing adding a loading resistor (on the secondaries, if I recall) to trim values... rules & guidelines there ? And is there any consideration necessary for the downstream linestage that will be driven by the Dac ? (or unnecessary, if a standard linestage...)

Okay, that's a lot -- guess I'm basically asking for a FAQ on tx-coupled-dac-output. Please presume a standard 2V dac output signal, and thanks for any of the requested info.

intermitten t
 
The first thing you have to do is pick a DAC chip, there is no standard solution because they are all different. Is the output current out or voltage out. What output level do you have to work with. Is it a single ended output or differential output. Does it have a DC component you have to deal with. Yes, some are easy to deal with, some are not, so generic questions and answers are difficult.
 
Thanks, here's a simple Q: in the context of the circuitry of a Dac, the output tranformer is referred to as an I/V transformer, current-to-voltage transformer.

What is it called in the pages of the transformer catalog ? (again, I'm a beginner at this)-- Is it an interstage, output, matching, transformer ? I don't see I/V listed as a type. Forgive this for being extreme novice question, but that's where I'm starting...
 
My interest is in substituting appropriate output transformers-- replacing output coupling-caps--- in a Teradak Nos Chameleon that I just got. It's chip complement is 16 paralleling TDA1543, Philips manufactured. Output is redbook standard 2v rms, single-ended, and-- that's all I see in terms of the output stage of the dac...

So am I just after some kind of high-spec, line-level, matching audio transformer that has good freq response figures ? Should it be the default 6oo : 6oo type ? Core type... ?

And I'm interested in shielding, too, since it would be entirely appropriate to fit this inside the enclosure of the Chameleon. (these are built to mod & so have lots of room to accommodate varying kinds of coupling strategies, etc).
Since size is relevant, something in the Lundahl or Sowter ranges seems to make sense.
But there are so many choices......

That's about what I know on the specifics...
Thanks for any pertinent info, whether generic or specific.
 
FWIW, I have built a DDDAC with 60 TDA1543's in parallell and used Lundahl LL1676's as output transformers in a parafeed arrangement. I kept the I/V resistors in place and connected a cap between the two primaries of the transformer. This option give me the chance to use both SE and balanced cables. I really like the sound of this DAC.

Geir
 
The loadresistor is 36 Ohm as per Doedes instructions. (180 Ohm/ dacboards) I have no clue what output impedance it has. I'm just thinkering and has implementied an idea I've had for a long time. The transformers are connected in a 1:2 configuration. Per Lundahl advised against connecting the secondaries in parallell. This gives me a little bit high output voltage, but my preamp doesn't seem to mind.

Geir
 
When used as an input transformer they recommend a source impedance of 600 Ohm and load impedance of 10KOhm.
I didn't think much about that because I used it mostly to be able to use balanced cables and thought that when used in a parafeedconfiguration that would be irrelevant. The loadresistor is placed across the primaries and not the secondaries as I've seen in other implementations.

Geir
 
-- guess I'm basically asking for a FAQ on tx-coupled-dac-output. Please presume a standard 2V dac output signal, and thanks for any of the requested info.

intermitten t

I guess my question is, if you don't know much about this, what made you decide to pursue it? Not criticizing, just asking.
I think this forum's Steve Eddy is a big transformer fan. You might want to search around for some of his posts.
 
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I guess my question is, if you don't know much about this, what made you decide to pursue it? Not criticizing, just asking.
I think this forum's Steve Eddy is a big transformer fan. You might want to search around for some of his posts.

Why not pursue.. ? Reading-up, learning, looking into new approaches, asking questions, doing mods, etc.. uhm, isn't that the theme of this board ?

What strikes me across all the different 'neighborhoods' of audio, whether moving-coil-stepups, tube-amp-outputs, etc --- is that a properly calculated Tx is often worlds better than other approaches. This is from listening; in reference to tx-coupling dac outputs, as you remark, no, I don't know much, but I notice it's not a completely unknown or undiscovered strategy.

So thanks, I'll try searching some SEddy posts.
 
My friend is going to mod my Lector cd player with the Superclock 4 and transformer coupling with Lundhal transformers. I am dropping it off to him today, I will post my impressions of what has happened to the sound.

He has turned me on to transformer coupling, he does not like caps, his preamp is transformer coupled 26 tubes and my God that thing is glorious!.
Also Reference Audio Mods is now doing mods that include transformer coupling with either copper or silver transformers. He uses Audio Consulting transformers, which may be his own brand.

There definitely is something to transformer coupling that I love, of course all the transformers I have heard used in this way were either, Tango or Black Art, all very high end trannies, cheap trannies might do more harm than good. All I know is that I was a changed man when I heard what transformer coupling does!


Mike
 
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