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Old 24th June 2010, 08:11 PM   #81
Marek is offline Marek  Poland
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This Analog Devices document was mentioned in this thread and it related to current output DACs. Sabre seems to be a voltage output DAC.
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Old 24th June 2010, 08:38 PM   #82
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Quote:
Originally Posted by Marek View Post
This Analog Devices document was mentioned in this thread and it related to current output DACs. Sabre seems to be a voltage output DAC.
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!"
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Old 25th June 2010, 08:42 AM   #83
Marek is offline Marek  Poland
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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:

Click the image to open in full size. Click the image to open in full size.

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.

Last edited by Marek; 25th June 2010 at 09:01 AM.
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Old 25th June 2010, 04:41 PM   #84
io is offline io  Hungary
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Hello

Hand made 1+1:2,2 ratio transformer spectrum analyzer yesterday
Sabre 195 ohm virtual (1800 ohm primer)
ref Pioneer PD8500
Attached Files
File Type: pdf Spectrum_1.pdf (9.6 KB, 186 views)
File Type: pdf PIO8500spectrum.pdf (10.1 KB, 130 views)
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Old 26th June 2010, 01:46 PM   #85
io is offline io  Hungary
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Transformer test for RMAA
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Old 26th June 2010, 03:01 PM   #86
Marek is offline Marek  Poland
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io, what sound device you used to record DAC output signal?
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Old 26th June 2010, 06:50 PM   #87
io is offline io  Hungary
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Linn Karik transport-- Sony test CD 0dB 1khz signal -BNC to BNC SPDIF transfer-Buffalo II- IV transformer-Xfi PC card-SpectraLAB
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Old 28th June 2010, 04:51 PM   #88
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io

Can You do 100Hz THD test..???

Rosendorfer.
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Old 28th June 2010, 06:26 PM   #89
io is offline io  Hungary
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yes, horrible
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File Type: pdf Spectrum_100.pdf (9.8 KB, 129 views)
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Old 28th June 2010, 06:37 PM   #90
io is offline io  Hungary
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Linn K3
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