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Old 11th December 2012, 05:40 AM   #391
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So there is no doubt, I have amended your diagram, so it should look like this:
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Old 11th December 2012, 10:55 AM   #392
rolls is offline rolls  Switzerland
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Thanks.
I suspect that using a step-up transformer with 1K on the Primary is not so good because the source Z of the DAC is way too high into the Primary.
Cheers, Joe
Who is the blame? I am using 1.2 Ohm, probably you misread my post??!!
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Old 11th December 2012, 11:18 AM   #393
rolls is offline rolls  Switzerland
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Yes, in my opinion that is what will get you the max results. It does two things, converts DC voltage offset to current offset, and creates the lowest impedance possible (our topic is Txs) into the Primary.
Cheers, Joe
There must be something in this grounding schema, that prevents people from doing/believing it, so they still ask about it.
I have thought about and would explain it this way:
Without grounding the mid point, it is for me like a class B amplifier. There is no current, when there is no sound. More loudness means more current, so the dac bounces between more voltage mode (loudness low) and more current mode (loudness high).
When grounding the midpoint, we have a class a situation, there is always a current flow.
I want to stress again, that the dac in current and hopefully passive mode sounds extremly well and can only be compared to the very best, i.e. Meitner. Best power supply is mandatory, I use LipoFe/NimH cells without any regs.
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Old 12th December 2012, 11:01 AM   #394
Ciu is offline Ciu  France
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There must be something in this grounding schema, that prevents people from doing/believing it, so they still ask about it.

When grounding the midpoint, we have a class a situation, there is always a current flow.
.
Hello Rolls !

If there is always current in primary, can use any transformer without gap ?
Untill now, I was using Jensen JT-11-emcf without grounding , with 6 ohms I/V from +- ess9018 output and tube stage 50x gain.
Thanks
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Old 12th December 2012, 11:43 AM   #395
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rolls means current flow that appears on DAC-resister-GND (not on primary)
Right?
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Old 12th December 2012, 02:55 PM   #396
rolls is offline rolls  Switzerland
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rolls means current flow that appears on DAC-resister-GND (not on primary)
Right?
Yes, current can just flow to ground, because there is the same tiny voltage on either side. Very thin wire is the best I/V resistor.
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Old 12th December 2012, 07:40 PM   #397
chaos is offline chaos  Austria
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i also want to thank mr. rasmussen! i listened for some months with a s&b tx103, 1:10, 2x 25R to ground. sounded very nice, but last week i changed to 1:5, 2x 1R to ground followed by a choke loaded 5842(130v, 15ma), choke input psu, superreg and i could not believe it. just fantastic:-))))))
will change the resistors to tx2575, cap to duelund.....nothing will beat this;-)
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Old 12th December 2012, 08:15 PM   #398
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Quote:
Originally Posted by rolls View Post
There must be something in this grounding schema, that prevents people from doing/believing it, so they still ask about it.
Maybe because this is a trick you can only do with Sabre DAC where you have a DAC with a 'voltage' offset. Try that with any of the other 'voltage' DACs or even 'current' DACs, and you will likely cause near instant damage.
You can do it with 'current' DACs like Burr-Brown 1792,1794,1796 DACs, as these have only a current offset (not a problem to deal with) and no voltage offset (much more tricky) and can be brought straight to Ground anyway.


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When grounding the midpoint, we have a class a situation, there is always a current flow.
When you have an output device, whether Fet or BiPolar, if you increase the current or 'bias' you also get higher transconductance and that should improve linearity. This is also a fact in Class A circuits, whether gain stages or buffers. So in this case it affects an internal change within the DAC by pulling out external current (again trading offset voltage to create offset current). But I believe there are a number of factors here, but this is an important one IMO.

Cheers, Joe
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Old 12th December 2012, 08:21 PM   #399
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Quote:
Originally Posted by chaos View Post
i also want to thank mr. rasmussen! i listened for some months with a s&b tx103, 1:10, 2x 25R to ground. sounded very nice, but last week i changed to 1:5, 2x 1R to ground... and i could not believe it. just fantastic:-))))))
I have been preaching this for near two years, and In think the penny is starting to sink in. I would not want to run the ES9018 any other way, it's needs to be pulled to a literal ground rather than a virtual one using the lowest value possible, as low as you can get away with.

Cheers, Joe
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Old 12th December 2012, 09:50 PM   #400
chaos is offline chaos  Austria
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.....using the lowest value possible, as low as you can get away with.

Cheers, Joe

so you think it would make sense to use the transformer in 1:20 and just take a wirewrap wire which would give me around 0,25R with a lenght of about 2,5"?
at least the transformer was made for voltages like this

cheers,klaus
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