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Buffalo II & transformers

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#82
Marek said:
This Analog Devices document was mentioned in this thread and it related to current output DACs. Sabre seems to be a voltage output DAC.
Click to expand...

Sorry, I haven't memorized all the posts in this thread. I thought it may be of some help to someone.

The Sabre can be used as current output or voltage output dependant upon what load impedance the output sees. Its internal source impedance is ~750 ohms per DAC, ~195 ohms for the 4 paralleled DACs in the Buffalo II implementation.

If you attach a load to the DAC nearer to zero ohms, the high source impedance will act as a current source. If the load is greater, the output gradually assumes a voltage source. Lots of gray area, and no abrupt knee where one becomes the other.

Look at Figure 11 in AN-912. On most current output DACs, Ra and Rb are external and the DAC has a limited output voltage compliance.

I suspect (I don't have the non-disclosed spec sheet) that in the Sabre DAC, Ra and Rb are internal, designed with a high voltage compliance. That's what makes the Sabre so exceptional to work with.

Its like the old SNL skit: "Its a floor wax!" "Its a desert topping!" "Its BOTH!" 🙂
 
#83
I've already tried BuffaloII in "current mode" with LL1931 (1:16) trafos loaded with 2,8kohm on secondaries. In this configuration DAC sees about 8ohm so every complementary output about 4ohm. I don't know if that is sufficient low to achieve good performance in current mode. If I reduce load resistance to 1kohm then every complementary output will see about 1ohm, ofcourse output level will decrease.

some RMAA measurments using motherboard built in sound card and crappy signal cable:

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


I don't know what is reason for this 10k+ peak..


and about Sabre DAC. As Russ said its internal equivalent scheme is voltage source in series with 195ohm resistance, not current source in pararell with resistance.
 
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#85
Transformer test for RMAA
 

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#98
jrenkin

Are You thinking of group buy... 😉

As far as I know there is nobody else trying to make his own trafos specially for our "beloved Buffalos".
I hope that with some more efforts io will come out with "Hand Made io-Trafo" for Buffalo …
Sounds interesting 🙂 ….

Rosendorfer
 
#100
Hello everybody,

Did enybody try output transformers with two buffalo II as dual mono ?

In dual mono mode i see (from the connection diagram with the IVY) that all 4 output signals (OUT_R+, OUT_R-, OUT_L+, OUT_L-) are used per channel, instead of 2 output signals per channel in stereo mode .
What would be the transformer connection diagram then?
 
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