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Old 19th February 2013, 04:51 PM   #431
loreliv is offline loreliv  Italy
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Quote:
Originally Posted by Joe Rasmussen View Post
I know where you are coming from. But the Sabre DAC is different from any other DAC, not just that it can be used in both modes - but arguably sounds best in Current mode IMO.

If you go back through the posts, see the ones that discusses the lighter tonal balance of the Sabre DAC is Voltage mode.

If you want to use Voltage, then transformer is the way to go. Many have heard me say that many times over, that with a differential voltage output where any DC offset will not be seen by the Primary of the transformer. But the Sabre DAC is not a conventional Voltage DAC.

The Sabre DAC has a much higher output Z than is usual for a Voltage DAC and hence there is reason to point to it as the cause of the light tonal balance when used as such. We need to reduce that Z and also force the DAC into current.

So, Voltage mode, use:

Click the image to open in full size.

The two resistors force the Sabre DAC into 3.14mA current offset while reducing offset voltage from 1.65V to about 1V. The output will be 1.3V RMS.

But how could this be applied to using Tubes and Current mode.

Pretty much all the post-DAC Tube designs I have seen avoid full-on Current mode. But with the Sabre DAC there is and opportunity if employing above suggestion repeated here:

Click the image to open in full size.

We can force the Sabre DAC into Current mode by pulling it virtually down to 0V DC and then get an offset current of 8mA. Using the same 1:1 transformer, it now opens up the way to use Current mode with Tubes.

So the above example shows how it can be done.

The point is that the Sabre DAC has flexibilities in the way that no other DAC has and using it in Plain Vanilla Voltage mode can be avoided as IMO it gives worst performance.

Cheers, Joe R.


hello all
I get disturb ....
I want to use the transformer jensen jt 11 EMCF with my buffalo dac II, but did not find in europe tx2575 resistance to 330R, but only, 270R or 390R, which recommended to take?
or is it better to buy other resistors 330R,?
thanks for the advice, greetings Loredana
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Old 19th February 2013, 07:58 PM   #432
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Quote:
Originally Posted by loreliv View Post
or is it better to buy other resistors 330R,?
If you got 270R, then use that. The output will be slightly lower.
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Old 1st March 2013, 09:50 AM   #433
mars2 is offline mars2  Switzerland
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Just recognized a few days ago, that this tread, which I followed some time ago with great interest, still exists and continues.

Me too, I took the "transformer-road" with forced current output.
I`m just listening to an 0.6ohm handwound silver-wire I/V-resistor, followed by a Lundahl LL1933 MC-stepup and a tube stage.

Sounds absolutly phantastic...never heard any DAC playing like this!

Have still a slight hum problem, which is due to the breadboard buildup of the output sage, I hope. Think, that I also opened up a whole bag of snakes because of the separate supplies (9 all together) of the buffalo and tube stage (sorry Russ and Brian I really had to do it.. and thanks specially to you Russ, Brian, Joe Rasmussen and others for pointing out tireless, that current mode is the way to go and starts under 1ohm I/V).

@rolls: do you have any problem with your silver resistors picking up noise? Maybe I have to shield them with some mu-metal cases.

P.S. Question: What do we have when anyone can afford buying the new silver Lundahl LL1933Ag and combines this one with an extra piece of silver wire?

The long time sought-after "purely passive silver bullet" !!!
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Old 1st March 2013, 12:15 PM   #434
mars2 is offline mars2  Switzerland
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I meant if someone can afford buying all this silver of course.
That anyone could afford it is a "Freudian slip" and my wishful thinking!
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Old 4th March 2013, 04:02 PM   #435
Coris is offline Coris  Norway
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Originally Posted by mars2 View Post
Just recognized a few days ago, that this tread, which I followed some time ago with great interest, still exists and continues.

Me too, I took the "transformer-road" with forced current output.
I`m just listening to an 0.6ohm handwound silver-wire I/V-resistor, followed by a Lundahl LL1933 MC-stepup and a tube stage.

Sounds absolutly phantastic...never heard any DAC playing like this!

Have still a slight hum problem, which is due to the breadboard buildup of the output sage, I hope. Think, that I also opened up a whole bag of snakes because of the separate supplies (9 all together) of the buffalo and tube stage (sorry Russ and Brian I really had to do it.. and thanks specially to you Russ, Brian, Joe Rasmussen and others for pointing out tireless, that current mode is the way to go and starts under 1ohm I/V).

@rolls: do you have any problem with your silver resistors picking up noise? Maybe I have to shield them with some mu-metal cases.

P.S. Question: What do we have when anyone can afford buying the new silver Lundahl LL1933Ag and combines this one with an extra piece of silver wire?

The long time sought-after "purely passive silver bullet" !!!
I just wonder how you made that resistor. You say "handwound", and I suppose is a wounded object. I think only that is unfortunate to have a such coil in that place... It should be an non inductive resistor, or it should be wounded in a special way to prevent parasitic inductance in the resistor.
I also think that it should be a slight small one resistor in that place...
As bigger is, as better act as an antenna for noises.
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Old 4th March 2013, 07:41 PM   #436
rolls is offline rolls  Switzerland
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mars2:
I have not any problems with noise, my "resistor" is about 1.1Ohms, end to end. Exact value is not important, I took a ruler , not an Ohmmeter.
Coris: If the wire is very thin, there is no need to wind it, and the sound is even better.
Mine is a piece of copper wire, 0.07mm, about 25cm long.
I have yet to buy a piece of Silver.
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Old 5th March 2013, 06:46 AM   #437
mars2 is offline mars2  Switzerland
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@Coris: I took wooden sticks of not quite 13mm diameter and tightly wound 0.2mm pure silver wire around it (36 turns). They should measure around 0.6 0hms, what they actually do.
Me too, I took a ruler for cutting them to the same lenghts, my ohmmeter isn`t that precise.
At least, they were dipped into beeswax for fixing the whole things.
You`re absolutely right, Coris. Having such coils in that place makes me thinking. They could really act as antennas and are too big (maybe I`d better used them as metal detectors).
Since there wasn`t enough space on each stick, I had to split them in two coils per side. Wish I could wind them at least bifilar for some inductive compensation.
But maybe a good shielding could straighten things out.

@rolls: I suppose, that your wire is straight or bended a little bit. So you shouldn`t have that problems. But how will you put it into an enclosure?
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Last edited by mars2; 5th March 2013 at 07:13 AM.
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Old 5th March 2013, 11:40 AM   #438
rolls is offline rolls  Switzerland
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Originally Posted by mars2 View Post
@rolls: I suppose, that your wire is straight or bended a little bit. So you shouldn`t have that problems. But how will you put it into an enclosure?
My solution is very untidy:
I have soldered the wires to the solder pins of the transformers.
These are in a wooden case on their own. I have soldered the earth wire to the midpoint, and fixed the joint to the wood with tape.
The wires are laying around the transformer.
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Old 5th March 2013, 10:19 PM   #439
mars2 is offline mars2  Switzerland
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Since I didn`t plan to build a receiver, Coris and you rolls speak from good sound with your copper solution, I was thinking about it.
I can`t live with that amount of hum and really tried a lot of different grounding schemes in the past (supplies noise is negligible), without getting things better...

So, early in this morning I went to my favorite electronic distribution store, where they still have a stock of different copper wire. I bought some 0.04mm. 5cm of this one will have around 0.7R.
This thing is tiny and thin like a hair. Wrapped that around a piece of printed circuit board (yes, that`s not really necessary, but easier for me to install in my nearly full populated enclosures, where space gets scarce) and soldered them in.

Et voilą! Ready are the new copper I/V-resistors (uuufffhhh...).

Powering things up and...yeah - near dead silence!!!

After a run-in period the music is there: smooth but detailed, sharp contoured but nevertheless colorful and warm. The instruments are exactly placed in the room and detectable...all together an impressive sound-picture of my records resp. files, as before.
Maybe there`s slightly less glare now, for some smoother sound with more silence in the background.

Somebody like me, who can`t afford silver stepups shouldn`t go for silver I/V resistors.
There`s more coherence now with my "purely passive copper bullet"
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Old 5th March 2013, 11:57 PM   #440
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Me too, I took the "transformer-road" with forced current output.
I`m just listening to an 0.6ohm handwound silver-wire I/V-resistor, followed by a Lundahl LL1933 MC-stepup and a tube stage.
Are you using the Lundahl transformers in 1:8 or 1:16 and can you please tell us what kind of tube output stage you have?
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