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Old 24th November 2011, 11:41 AM   #231
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Originally Posted by Joe Rasmussen View Post
Three points, you miss out on the better performance using both phases; you need a coupling capacitor; and you only get 1V output when using ES9018 in stereo mode.
Cheers, Joe R.
Better performance when using long cables, when short cable to SE amp input no difference.
I'm not using stereo, 4 single channels not paralleled. I don't know if I require 2V RMS, but with current output 50% of signal level is more than enough for me.
What does it mean 1:10 transformer prim-sec ratio? What kind of core shall it have, it's wattage, how many turns, what wire?
Have you mentioned voltage output in your schematic? Why should we increase input resistance of the primary with those 195R resistors? Does lower input resistance worse in case of current output?
I this is differential conversion, GND return shall be taken directly from ES9018 out? If I have SE amp, can this transformer convert differential current output to SE voltage output?
Regards.
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Old 24th November 2011, 12:13 PM   #232
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Originally Posted by AndriyOL View Post
Better performance when using long cables, when short cable to SE amp input no difference.
Sorry, but this is completely incorrect. the reason is that all of the stuff that is common mode and designed to be rejected by I/V stage will simply pass right through unfiltered.

You will never get the most out of the DAC this way. Both THD and DNR will suffer greatly, and the noise floor will be much higher.
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Old 24th November 2011, 12:27 PM   #233
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In my opinion it is simply is not possible to run directly (even with resistors) into *any* transformer and keep the DAC in "current mode". This is because I would never consider anything more than 1ohm seeing a 195ohm source impedance as approximating an infinite impedance ratio. Your still modulating the outputs of the DACs far more than is desirable even at 5-10 ohms. It is about ratios. 195R Is low output impedance. So to make 195R look like a current source the load has to be an incredibly small impedance. I am sorry to say this but even 2 ohms in not small when looked at in those terms. That ratio is only ~100. Certainly not large enough.

On a personal note - having listened to the ES9008/12/18 for as long or longer than anybody on earth (well other than possibly Dustin and crew) I can say emphatically that I absolutely hear a difference when the DAC is loaded into a virtual ground as apposed to even a smallish resistance (2-10 ohms). Very subtle but it does lose something in my opinion. I have heard hundreds of output stages on the Sabre and designed quite a few (only some of them make it onto these pages).

The bottom line is you absolutely shouldn't choose to use transformers because you want current mode. You simply can't get it. Choose them because you like the way they sound! It is the same argument for tubes. It is perfectly OK to prefer any output stage on the basis of things that go beyond ideal measurements and extend to taste.

Now I do think the smaller the impedance the better, this of course extends to transformers, but you are *always* going to be using the DAC like a voltage source when using transformers. There is nothing wrong with that.

Happy Thanks Giving to all!

Cheers!
Russ
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Last edited by Russ White; 24th November 2011 at 12:33 PM.
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Old 24th November 2011, 10:40 PM   #234
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Quote:
Originally Posted by Russ White View Post
In my opinion it is simply is not possible to run directly (even with resistors) into *any* transformer and keep the DAC in "current mode". This is because I would never consider anything more than 1ohm seeing a 195ohm source impedance as approximating an infinite impedance ratio.
Absolutely agree with that, it virtually has to see zero Ohms and indeed IF zero Ohms then, and only then, would you achieve infinite ratio.

So those resistors and their values are about compromises and the degree to which we make those and what the benefits are. If you want to use transformers, then it will never be true current mode. No question about that.

Joe R.
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Old 24th November 2011, 11:36 PM   #235
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Originally Posted by AndriyOL View Post
What does it mean 1:10 transformer prim-sec ratio? What kind of core shall it have, it's wattage, how many turns, what wire?
That is up to you. I suggest that you buy a suitable transformer like maybe Sowter Type 9545 DAC INTERFACE TRANSFORMER.


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Why should we increase input resistance of the primary with those 195R resistors? Does lower input resistance worse in case of current output?
No, there are no added 195R resistors, these represents the internal impedance of the ES9018 when used in Stereo mode.

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Originally Posted by AndriyOL View Post
I this is differential conversion, GND return shall be taken directly from ES9018 out? If I have SE amp, can this transformer convert differential current output to SE voltage output?
Regards.
That is pretty much the idea. Works both balanced and unbalanced. If unbalanced, use a floating RCA and let the Interconnect provide the grounding at the preamp end. That way you get galvanic isolation even if unbalanced - the two grounds will be kept separate.

Cheers, Joe R.
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Old 25th November 2011, 04:36 PM   #236
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That is pretty much the idea. Works both balanced and unbalanced. If unbalanced, use a floating RCA and let the Interconnect provide the grounding at the preamp end. That way you get galvanic isolation even if unbalanced - the two grounds will be kept separate.
Could you please elaborate this in a schematic.
Thanks.
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Old 28th November 2011, 09:24 AM   #237
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Default 1.3 Vrms !!

Hello

nobody answered the question: with C configuration is really 1.3Vrms sufficient to drive any preamp?

Pierre
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Old 28th November 2011, 11:25 AM   #238
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Hello

nobody answered the question: with C configuration is really 1.3V rms sufficient to drive any preamp?

Pierre
For sure. Those who use so-called passive preamps may find -4dB noticeable, but use any proper preamp and -4dB is nothing to worry about.

Cheers, Joe R.
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Old 29th November 2011, 12:15 AM   #239
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In my opinion it is simply is not possible to run directly (even with resistors) into *any* transformer and keep the DAC in "current mode". This is because I would never consider anything more than 1ohm seeing a 195ohm source impedance as approximating an infinite impedance ratio.

Now I do think the smaller the impedance the better, this of course extends to transformers, but you are *always* going to be using the DAC like a voltage source when using transformers.

Russ
Who says you can't use a transformer in 'current mode' ?

Do a search on "zero field transfomer".

There are various implementations and I've even cooked up some of my own
sans opamp. With mixed feedback you can make the IP Z whatever you like.
Without it, just use a very low winding resistance transformer.

T
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Old 29th November 2011, 11:52 AM   #240
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Originally Posted by Terry Demol View Post

Who says you can't use a transformer in 'current mode' ?

Do a search on "zero field transfomer".
Hi Terry

Shows you can do a lot with feedback. But as a wise man once said "all things may be possible, even lawful, but not all things are advantageous." Seems the guy's name was Saul or Paul or something.

Come around and listen to the Oppo 95 here, puts a smile on my face. Need two clocks though, makes a real difference.

Cheers, Joe R.
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