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Old 28th February 2008, 02:15 AM   #111
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Quote:
Originally posted by Russ White


From the white paper.



Thanks Russ,

So this implies that it is similar to a voltage source with 800R
in series with each OP?

If this is the case why is there better performance when
operated in so called current OP mode?

Cheers

Terry
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Old 28th February 2008, 02:46 AM   #112
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Now I could be wrong here, but in my limited experience it is because a voltage source in series with a resistance is in essence, a current source.

This DAC is simply closer to an ideal current soure than it is to an ideal voltage source. Ideal voltage sources have 0 output impedance, ideal current sources have infinite output impedance. Now 200R is hardly infinite, but it is infinitely larger than 0.

Current sources perform best into a low impedance node. So what is called for is an inverting type opamp circuit or similar I/V scheme.

Feel free to correct me if I am mistaken.

Cheers!
Russ
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Old 28th February 2008, 03:01 AM   #113
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Quote:
Originally posted by Russ White
Dustin,

A quick question for you if I may.

What mechanism is used for volume control on this device?

It appear from the datasheet that the volume control is analog, and not done in the digital domain. Is this correct?

The reason I ask, is that noticed in the datasheet a blurb about 64 intermediate steps between .5db steps, so I am suspecting there must be some switching involved. Does this mean its an analog attenuation?

Thanks!
Russ
Hi Russ,

The volume control is done just before the oversampling filter on the digital data. It can be set to 0.5dB increments, but in order to avoid clicking upon volume level changes, it acutally goes through 64 intermediate levels to move 0.5dB. And op top of that, the volume does not instantly change when you request, rather is logarythmically moves to the desired level. The way this shows up in a system implementation is that the sound softly changes levels. (somehitng I like)
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Old 28th February 2008, 03:02 AM   #114
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Quote:
Originally posted by Terry Demol


Hi Dustin,

Very impressive work.

Can you divulge what the OP impedance of each DAC is?

This is important, for example, when choosing a suitable I-V opamp
or discrete architecture as lower Z means higher effective gain,
especially in 2 ch mode where all the OP Z's will be in parallel. The
I-V 'virtual' gain can end up being significant. This will also affect
the linearity of the I-V.

Thanks,

Terry

Each pin is 781 Ohms output impedance.
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Old 28th February 2008, 03:06 AM   #115
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Quote:
Originally posted by Russ White
Ok so if I am reading the datasheet correctly, if you want to support 192/24 spdif input you will need at least a 74.112mhz clock.

I like to use the Crystek C33xx the closest I can find is 75mhz, but I wonder if 80 or 100mhz would work better. They are great XOs.

What do you recommend Dustin?

Hi Russ,

I would use 80MHz. By the way, running the DAC at 80MHz with a good Xtal you can expect to only see a 1dB DNR loss form teh 40Mhz boards, if that. Some show no diff, some showed 1dB.

Dustin
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Old 28th February 2008, 03:10 AM   #116
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Quote:
Originally posted by Terry Demol



Thanks Russ,

So this implies that it is similar to a voltage source with 800R
in series with each OP?

If this is the case why is there better performance when
operated in so called current OP mode?

Cheers

Terry

Quote:
Originally posted by Russ White
Now I could be wrong here, but in my limited experience it is because a voltage source in series with a resistance is in essence, a current source.

This DAC is simply closer to an ideal current soure than it is to an ideal voltage source. Ideal voltage sources have 0 output impedance, ideal current sources have infinite output impedance. Now 200R is hardly infinite, but it is infinitely larger than 0.

Current sources perform best into a low impedance node. So what is called for is an inverting type opamp circuit or similar I/V scheme.

Feel free to correct me if I am mistaken.

Cheers!
Russ

No correction needed
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Old 28th February 2008, 03:17 AM   #117
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Dustin-

Do you have any idea (or gut feeling) of the recent acquisition will affect chip availability?

Thanks!
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Old 28th February 2008, 03:18 AM   #118
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Quote:
Originally posted by BrianDonegan
Dustin-

Do you have any idea of the recent acquisition will affect chip availability?

Thanks!

Availabiilty is not affected at all
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Old 28th February 2008, 05:56 PM   #119
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Hello Dustin,

I have the demo board for the Sabre DAC. The GUI tells me USB Device not found. When plugged into the USB port Windows (Vista) searches for a driver, but cannot find one. Is there an additional driver I need?

I intend to use S/PDIF with the DAC.

Many thanks.
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Old 28th February 2008, 05:59 PM   #120
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The driver is located in the

\Sabre8_GUI\USB Driver


where Sabre8_GUI is the directory you installed the app into.

When you plug the board in, just point to the "Sabre8.inf" file in that folder. Should work as we have tried it here on vista with no issue. Let me know.


Thanks

Dustin
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