Buffalo II & transformers

[Russ White]

Originally Posted by WDYSUN

what would happen if you don't have the tube stage in the schema, but ths signal would go with a short wire to a buffered tube preamp with a short wire? Would the trafo output still work ?

Best
Pierre

Yes, the signal will just be quite small.

[WDYSUN]

Originally Posted by Russ White

Yes, the signal will just be quite small.

in general how large a signal from a DAC should be bofore to enter a (input) buffered well done tube stage with a *regular* gain?

Pierre

[Joe Rasmussen]

Originally Posted by AndriyOL

What is the purpose of the transformer if you have voltage output?

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:



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:



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.

[Joe Rasmussen]

Originally Posted by Russ White

Yes, the signal will just be quite small.

Hi Russ

Indeed it will. The maths are simple. With the example shown 30mV RMS and if a full output of 2V is required, then the tube gain needs to be 66 approx. But most of us can get away with less than that. The 3R value can be tweaked too.

I am not about to do it myself, at least not for now but might a little further down the road, or likely help a fellow DIY'er to do it, that being more likely.

Cheers, Joe R.

[Gluca]

Hi

I tried the BII with 600:600 transformers, 10k:10k and 150:10k transformers so ranging from current to voltage mode with minimal changes to the output stage (tube): best result so far I had and sticked to is with 10k:10k transformers, it seems the sabre likes this high impedance better.

[WDYSUN]

Hi Joe

Originally Posted by Joe Rasmussen

...
So, Voltage mode, use:

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.

so if I got you right, suppose I'll go for "C", you are saying that with 1.3V RMS I go straight to my tube preamp (?)

Best
Pierre

[AndriyOL]

Originally Posted by Joe Rasmussen

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.
Cheers, Joe R.

I use Sabre in voltage mode without transformer directly to amp. Only positive and GND pinouts. My guess no need to convert from differential to SE, as negative signal is the same, only opposite phase. Benefit of using transformer can be with current mode.
Could you suggest suitable transformer parameters for ES9018 dac in current mode?

[Jeffrey Davison]

Schematic?

Thanks

JD

Originally Posted by staccatiss

New Japanese ESS9018 IV Transformers –a mini review
Executive summary: these new Japanese transformers are the best sounding IV transformers that the author have ever listened to, and compared to a highly modified Legato and a fully discrete all-FET IV converter, these transformers are sonically hard to beat.


I have tried both the amorphous core Lundahl LL1684 and Sowther 9545e audio transformers applied as IV converters, and although the sound has been good with the LL1684:s, and OK with the 9545e:s, they did not sound as good as the discrete IV converters I have. I actually gave up on transformers even though they had something special sonically. Instead I started to modify and upgrade my Legato, IVY, and fully discrete FET IV converters with new components, and the power supply super shunt regulators were modified as well.

I thought that I´d given up on transformers as the ultimate IV converter, when a few months back, Bunpei wrote to me about a new Japanese transformer distributed by Feastrex*, that was made especially for the ESS9018 DAC, and that this transformer used a special type of core material called FINEMET, which is a nano crystalline soft magnet material. I checked out the new material and got a few photos of the transformers, and two weeks later, I had a pair of unusually heavy transformers hooked up with solid core silver wire to my reference DAC, the Buffalo II with the three Tridents installed, playing music from the SDTrans384 memory card player I use daily.

Compared to having a dual mono, discrete IV converter with dual toroids for raw power supply, and dual super shunt regulators to feed the converters, hooking up a similar transformer setup, is unstressingly easy. For each channel, just connect two (GND is not needed) short wires from the Buffalo2´s output to the transformer, connect the three or two wires (balanced or unbalanced) from the transformer outputs to the line amplifier, and voila, you are done! Well, OK, you need to have a load resistor on the transformer outputs and maybe a small capacitor across the secondaries, too.


I used a 4,02k TX2352 bulk metal foil resistor connected directly at the transformer outputs as load resistor to get 2,0Vrms at 0dBFS into the Buffalo2. A 10nF RIFA PFE210 film and foil polystyrene capacitor was also soldered to the outputs, as I, on my oscilloscope, noted a ringing when only a resistive load was used. The cap removed the ringing, and also made the treble sound as it should. For the experimental person, lower resistance values and made of other resistor materials, and ditto for the capacitor could be fun try out. If a lower output voltage is wanted, just lower the resistor value. One could even use a volume control of top notch quality connected at the secondary windings to get the master volume control for one´s complete hifi system.


To make the comparisons between - first the Legato and the transformers - and secondly between the all-FET IV converter and the transformers, I used two identical Buffalo2 DAC:s that were both powered by identical Placid super shunt regulators. The two Buffalo2:s were via I2S connected to a single SDTrans384 memory card player. One of the Buffalo2’s was always connected to the transformers, whilst the other Buffalo2 was connected either to the Legato or to the all-FET IV converter.

After a week’s burn-in of the transformers using the repeat functionality of the SDTrans384, I started out to compare my Legato, with Duelund VSF 10 uF caps and only film and foil polystyrene caps for the other caps, against the transformers. These transformers, in general, sound more clean or pure, less foggy, and less fat. The bass is deep and more articulated from the transformers but the Legato has more fattiness and more weight. About like from a high Q loudspeaker. Women´s voices are clearer to hear with the transformers but maybe they lack a bit of “body” in the voices – or this is how it should sound like if the fog is removed.


The transformers have more accurate energy in the treble which might be disturbing listening to for ex “Love over gold” which, IMO, is having a too harsh treble. The Legato smoothes this over and makes the song almost enjoyable. I am very sensitive to bad sounding s- and tch-sounds from voices and these sounds are better reproduced with the transformers. Listening to snare drums or steel stringed acoustic guitars there is more snap and attack.


Exchanging the Legato for my reference, the all-FET IV converter, which also uses a TX2352 resistor in the most critical position, I immediately noticed that it has the same accurate energy in the treble, that the transformers have more articulation in the bass, and as earlier with the Legato, the transformers do not have the sound of a high Q loudspeaker. I am really like the bass reproduction of these transformers. It is deep and firm but not even a tad dominant over mid or treble.

Compared to the transformers, the treble from the all-FET converter sounds a bit cloudy. For ex. cymbals and tambourines sound more real with the transformers, with less hash and more details. Male voices have a tad less body from the transformers but this is more and more feeling as correct. The all-FET converter has a more forward reproduction with more authority and I get the feeling of a demo type reproduction.


What made me decide to use the Feastrex transformers as my reference IV converter, was that when I listened to a duet between a male and female singer. They sing at the same time, and both singers were positioned at the same spot in the 3D image. With the all-FET converter (and also the Legato) it was hard for me to hear every word that the woman sang, but with the transformers I could pick out every word. They are very detailed.


Seems like I will be enjoying transformers for a while J. As I like to experiment, I will be trying an Audiocap Teflon and tin foil capacitor, and also a Caddock Mk132 as load resistor.



At the type writer - Staccatiss

*Feastrex, a Japanese full range loudspeaker driver company, is distributing the ESS9018 transformers, but the design of the transformer is made by Mr. Yasuo Suzuki - a “typical” Japanese audiophile. Primary DC resistance is 14 Ohms, and secondary resistance is 16 Ohms, and the turn´s ratio is 1+1:1+1. The transformers can be had with black urushi coating that is supposed to dampen against microphony.

Information about FINEMET can be found here http://www.hitachi-metals.co.jp/prod/prod02/pdf/hl-fm9-e.pdf.

[Joe Rasmussen]

Originally Posted by AndriyOL

I use Sabre in voltage mode without transformer directly to amp. Only positive and GND pinouts. My guess no need to convert from differential to SE, as negative signal is the same, only opposite phase.

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.

Originally Posted by AndriyOL

Could you suggest suitable transformer parameters for ES9018 dac in current mode?

You will need a loading resistor across either Primary (I would think preferably) or Secondary and a 1:10 (or more?) step-up. A good step-up transformer needs to be chosen with some care.

Others may choose to comment on this?

Cheers, Joe R.

[Joe Rasmussen]

Originally Posted by AndriyOL

Could you suggest suitable transformer parameters for ES9018 dac in current mode?

Try this:



I would likely use 15R = 1.35V RMS out.

Cheers, Joe R.