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Old 21st January 2013, 09:38 PM   #411
chaos is offline chaos  Austria
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@ rolls: silver, copper...there is small difference. i use it for fine-tuning. but right now i wait for my plate chokes...many m of copper
what i dont know, does it make sense to go really low with the value of the I/V resistor? lower than 0,5R? down to 0,125R?
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Old 22nd January 2013, 01:04 PM   #412
rolls is offline rolls  Switzerland
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Quote:
Originally Posted by RollE2k View Post
Have ANYBODY tried running dual mono Buffalo/ES9018's with step-up transformers?
I'm thinking this would be the best of two worlds. since you would have approx 32mA per channel it would be possible to load each phase <1R, and since the output impedance would be so low, it would be possible to run 1:32 transformer.
It is not the best of two worlds:
- With lower input impedance, there is lower output impedance, correct, but useless. If you have an active gain stage with lets say the "official" 47k, there is no benefit of a lower output impedance.
- An important part of this thread is about lowering the resistance seen by the dac, but this is true only if we mean the same amount of parallel dacs. Normally we mean the output of 4 parallel dacs in the Sabre chip. So we should not speak of resistance any more if we change the number of dacs. We should speak of the real important parameter: Output voltage of the parallel dacs in current mode. It should be as low as possible as well, but now we see what happens, if we use a board in mono mode:
Output current is doubled, resistance is divided by 2, output voltage is the same! So in mono mod you must lower the resistance just to keep the same output voltage!
There is only one reason to use 2 chips in mono mode:
Because more dacs are involved, THD is lower, and it sounds better,
but we have yet to ask people, who have done it.
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Old 22nd January 2013, 02:35 PM   #413
RollE2k is offline RollE2k  Sweden
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Well of course, i know that the important part is to get the dac-chips in "current-mode" which is why, in dual mono, i will get twice the current (and hence twice the voltage output with same loading). Also, lower output impedance, makes it possible to use higher step-up ratio on transformer without having many K-ohm output impedance.

So why is say "best of two worlds", is because at least on paper - for my application, this would mean that i could lower the loading of dac-output, while i still get lower output impedance from the transformers and at the same time higher output level.

Anyway, will be interesting to see how it sounds for chaos if he tries lower loading with step-ups.
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Old 22nd January 2013, 03:22 PM   #414
rolls is offline rolls  Switzerland
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Quote:
Originally Posted by RollE2k View Post
Well of course, i know that the important part is to get the dac-chips in "current-mode" which is why, in dual mono, i will get twice the current (and hence twice the voltage output with same loading). Also, lower output impedance, makes it possible to use higher step-up ratio on transformer without having many K-ohm output impedance.

.
Sorry, but you miss the point: If you load the mono dac with the same resistor, the voltage doubles, and that is worse for the sound!
Zero voltage means perfect current mode, full voltage means obviously voltage mode.
I have yet to find the point where current mode audibly worsens,
at the moment I have about 0.55R per side, stereo dac, must be totally around 6mVrms.
And even with a higher step up ratio output res would still be lower than 47k.
I have seen that you have been trying hard to find the best solutions for the Buffalo dac. I am interested to learn, how you use it at the moment, I mean which power supply, transformer and/or active stage.
Sharing experiences is a valuable part of a thread.

I have already posted my implementation above, still no active gain stage at the moment.
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Old 22nd January 2013, 04:47 PM   #415
rolls is offline rolls  Switzerland
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Quote:
Originally Posted by chaos View Post
@ rolls: silver, copper...there is small difference. i use it for fine-tuning. but right now i wait for my plate chokes...many m of copper
what i dont know, does it make sense to go really low with the value of the I/V resistor? lower than 0,5R? down to 0,125R?
You have a good implementation to experiment with different resistors, because your tube stage has high input resistance, so you could play with different resistors. I can not do this at the moment, because I have no active stage, higher would mean to high on the secondary for the TVC, and lower would mean too low even for the horn. I tried 2.2 Ohm, was not so good, but the reason could have been "leaving current mode" or secondary impedance too high.
If you take thin wire, it costs you nearly nothing, and the sound is still better than even a Texas, and we should grasp the chance to use wire, it is only possible with very low values. Cut a length, fold it in the middle to solder to an earthpoint. If you still want the Texas, you can find the critical point with wire and then buy a Texas. There is just one drawback I noticed even or especially with thin wire: You need at least 20 hours burn in. This would mean soldering very thin wire, playing a CD for 20 hours, listen seriously, ....
Lets solve the big question: where is the border, where does current mode becomes audibly worse?
I have yet to decide to build an active stage after the 1:25 transformer. It sounds extremly smooth yet detailed, in front of me,
without all the artifacts of the mains, regulators.
Nevertheless I could need a bit more power, actually my dac has to drive a transformer, a TVC, 2 interconnects and the power amp, could be too much for the tiny chip.
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Old 22nd January 2013, 05:06 PM   #416
RollE2k is offline RollE2k  Sweden
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Well, i didn't think about it that way. So probably the only better thing when running step-up and dual mono is that you could go for a higher step-up ratio with the lower loading of the dac in my case. (to get higher signal level).

Well, i don't own the dac yet - i'm the kind of guy who try to learn before buying.
But i will feed the dac with SSLV1.1, and i'm thinking about getting Ian's FIFO, but not shure about that yet. The problem for me is room, so i'll have to decide between active gain stage or FIFO/reclocker.

All, this will be built into my line-stage case, where i have approx 11,5dB gain - and i would like to have 2.0 - 2.5vRMS out from the line stage.
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Old 22nd January 2013, 07:29 PM   #417
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I don't read this thread much, but I did today for some reason. Let's keep it on topic.
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Old 22nd January 2013, 08:03 PM   #418
rolls is offline rolls  Switzerland
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Quote:
Originally Posted by RollE2k View Post
Well, i didn't think about it that way. So probably the only better thing when running step-up and dual mono is that you could go for a higher step-up ratio with the lower loading of the dac in my case. (to get higher signal level).

Well, i don't own the dac yet - i'm the kind of guy who try to learn before buying.
But i will feed the dac with SSLV1.1, and i'm thinking about getting Ian's FIFO, but not shure about that yet. The problem for me is room, so i'll have to decide between active gain stage or FIFO/reclocker.

All, this will be built into my line-stage case, where i have approx 11,5dB gain - and i would like to have 2.0 - 2.5vRMS out from the line stage.
I am with you, but just up to a certain degree. Just have a look at your own list of posts, then you know what I mean. You have been "waiting" for years. Buy a Buffalo, switchboard is not important. When you listen for the first time, you will ask yourself: why didn't I buy it years ago? I still have a 24dB Dac, sounds fantastic with batteries.

Last edited by BrianDonegan; 22nd January 2013 at 08:10 PM. Reason: Removed taunting...
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Old 22nd January 2013, 08:14 PM   #419
rolls is offline rolls  Switzerland
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Originally Posted by BrianDonegan View Post
I don't read this thread much, but I did today for some reason. Let's keep it on topic.
I totally agree, verbal arguments are always welcome, thank you.
André
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Old 10th February 2013, 08:09 PM   #420
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
sorry for the silly question .....
but where you found, the resistor 195r, to be used in series with the transformer jensen jt 11 EMCF?
I can not find this value .....
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