ESS Sabre Reference DAC (8-channel)

[Russ White]

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

From the white paper.

The default configuration, in eight channel mode, is that a
pair of six bit DACs operating in anti-phase make up each
channel. Since the DACs are as described, namely a Thevenin
equivalent to a voltage source linearly between AGnd and
AVcc having an approximately 800Ω output impedance, you
may choose to connect this output to a voltage mode (noninverting
amplifier) configuration; or you may choose to
connect it to a virtual ground current mode (inverting
amplifier) configuration. The highest performance in terms of
THD is via the current mode16, but both voltage and current
mode provide about the same DNR.

The default configuration for Stereo mode, and the only
configuration that can use the SPDIF input, is to wire four
output channels in parallel. When Stereo mode is enabled in
the configuration registers the same data is sent to all four
channels. Effectively now the DACs become a pair of eight bit
DACs having an output impedance of about 200Ω. This
configuration allows >132dB of DNR to be typically
reached17. THD in the Stereo current mode is limited by the
external components and measurement equipment. We
recommend using an extremely good op-amp for the highest
performance but even an excellent op-amp is the limiting
factor in the THD18.

 

[rossl]

Hi Ross,

I will actually probably use a PIC24 type device on my board simply because I am most familiar with it, and it has built in I2C and SPI peripherals.

Hi Russ

I ordered some PIC16F677 parts. They should be here tomorrow or Friday. That looked to be the smallest and cheapest one that has a MSSP controller for I2C.

 

[Dougie085]

Russ, Does your PCB you've laid out so far use SMT?

 

[Russ White]

Russ, Does your PCB you've laid out so far use SMT?

Yes, its essentially the same style layout as our current versions of the Opus and COD DACs. It will be the same form factor.

It will have a basic on board controller which can be disabled in favor of external control.

Common configuration changes will be made via tri-state switches.

For reference, here is the current Opus:

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

Cheers!
Russ

 

[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?

 

[Dougie085]

Awesome the Opus is very nice

 

[Russ White]

ok to answer my own question it look like the minimum MCLK cycle time is 13ns.

1/13E-9 is 76.923Mhz

So a 75mhz XO "should" work and allow 192khz SPDIF I think....

Well I will await Dustin's response.

Cheers!
Russ

 

[Dougie085]

Russ are you thinking you guys might offer this as a kit or just thinking of the PCB for the most part? I'm guessing that depends on how much you like it.

 

[Russ White]

It would be a complete module, like the Opus. But would sell bare PCBs too.

Cheers!
Russ

 

[BrianDonegan]

If we do sell a kit, it would most likely come with the chips permounted. There is also the question of programming the uC.

 

[Terry Demol]

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

 

[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

 

[dusfor99]

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)

 

[dusfor99]

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.

 

[dusfor99]

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

 

[dusfor99]

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

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

 

[BrianDonegan]

Dustin-

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

Thanks!

 

[dusfor99]

Dustin-

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

Thanks!

Availabiilty is not affected at all

 

[Spartacus]

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.

 

[dusfor99]

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