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Old 26th September 2008, 03:53 PM   #1011
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Default Re: Corrections I should of made a while ago

Hi Dustin et all: Indeed, credit is due for Twisted Pear's Buffalo being first out the door; the fact that it exists calls for attaboys and kudos. I appreciate them every time I fire it up. The good news / bad news about being a "pioneer species" is that there will be feedback from other critters showing up later on the landscape.

That the Sabre chip is more than holding it's own in comparison with ridiculously more expensive hardware is impressive.

Somebody, maybe TP, (not me! I think retail is for masochists, but am glad somebody else is doing it) is going to come up with a kickass, tricked out implementation of the Sabre for waay cheap, maybe usb and spdif versions.

rossl: I did a simple test (borrowed time at a telecom lab, HP spec analyzers) of jitter induction thru shared supply lines: an xtal osc with it's own reg through a simple 74xx04 with it's own separate reg. The spectrum of the phase noise "skirt" looked virtually the same, except when a digital signal was sent through another section of the 04: the spectrum at the osc remained clean, but there were spurs, correlated of course, easily 20 dB above the phase noise floor at the 04 output. Subjectively, I find correlated stuff to be more annoying, whereas random stuff tends to be either pleasant or boring.

Share and enjoy,

WMS
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Old 28th September 2008, 02:48 PM   #1012
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Quote:
The good news / bad news about being a "pioneer species" is that there will be feedback from other critters showing up later on the landscape.
Definitely good news as far as I am concerned.
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Old 12th October 2008, 12:08 AM   #1013
rossl is offline rossl  United States
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Default Sabre8 prototype DAC

My Sabre8 prototype is turned on and making music.

The circuit board. It is a 4-layer boards. There was a few problems with the first one so this one is revision B. I was able to tweak the first one to get excellent sound and I made those changes in this version.

Layer2 is a solid ground plane. All digital traces are impedance controlled. The analog section has an AVCC plane and planes for the +/- analog supplies. Digital side has plane for 3V3.
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Old 12th October 2008, 12:13 AM   #1014
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The chassis was custom made. I thought the chassis would come out a darker blue. Next order I may stick with plain black matte with the light blue silkscreen. I will get a different font next time also.
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Old 12th October 2008, 12:14 AM   #1015
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The front panel
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Old 12th October 2008, 12:16 AM   #1016
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The DAC features a 4-input switch and a processor loop. The processor loop allows the switched signal to be sent out to a DSP equalizer and then returned to the Sabre8.

After the input switch the switched signal is sent out a TOSLINK port and also goes to a mux. A front panel switch controls the mux and selects either the switch output or the processor loop input.
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Old 12th October 2008, 12:17 AM   #1017
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Differential output stage. It features symettrical and balanced IC opamp IV conversion. That is followed by an IC opamp filter/driver stage that drives the transformers with a very low impedance.
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Old 12th October 2008, 12:19 AM   #1018
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With the front panel off
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Old 12th October 2008, 12:20 AM   #1019
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PIC processor is in the center. The 20-pin DIP in the socket.

There are over 200 caps on the board and over 150 resistors.
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Old 12th October 2008, 12:22 AM   #1020
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It uses a 5-watt switching power supply that switches at 100KHz.
The outputs are filtered and post-regulated with seven linear voltage regulators.
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