Buffalo II

[Russ White]

Hi Owen,

I have looked closely at your cct. And it indeed looks intriguing. Very nice work. I truly hope it is a success.

I still have a bit of fear regarding transient conditions if the DAC is powered down prior to the output stage running out of steam.

I have simulated the cct and the result was a very large transient which aligns with my practical experience.

I trust your work, and I don't mean to second guess you at all. Perhaps I am missing something.

now if one can insure that the output stage always is off prior to the DAC then your are golden.

As for the input impedance of the CP-II it is well under 500 milliohms. And I think I can get it a bit lower. It has neither startup or shutdown transients.

Cheers!
Russ

[Russ White]

Originally Posted by DSP_Geek

Russ, how much current does each BII take? Would the 9+9V transformer cover three of them with Placid supplies?

hmm you would need 750ma total. So 375ma per secondary (I would run them parallel). If you use the ones we supply (15VA) you should be just fine.

Cheers!
Rus

[Spirit02]

Russ, could you check your pms or orderstatus@tp email please?

[steve jones]

A couple of questions for Russ while I eagerly await my Buffalo II boards.

IC7 on the new Buffalo II board, what is part # is supplied for the SPDIF comparator?

For the SPDIF connection, is there a 75 ohm termination resistor provided on the board, or does that need to be accounted for by the end user?

Many thanks!

[BrianDonegan]

IC7 on the new Buffalo II board, what is part # is supplied for the SPDIF comparator?

For the SPDIF connection, is there a 75 ohm termination resistor provided on the board, or does that need to be accounted for by the end user?

The comparator is a LMV7219. There is a termination resistor on the bottom of the board.

[steve jones]

Thanks Brian. Looks like you guys have thought of everything.

[Woodenhead]

Hi Russ/Brian,

You've said the BII draws 250mA, but do you have the current draw for the IVYIII? If possible, each IV stage and the ballsie.

Thanks!

[Russ White]

It has become clear to me the some folks do not understand what the 1.2V VDD supplies on the ESS9018 and its cousins do.

The 1.2V supplies only do two things in the DAC, the first is that it drives the core of the chip. This is of course crucial. The second is it drives the gates of level shifters (a high impedance) into the quantizers.

It is important to understand what these level shifters do. They simply shift the bits from 1.2V core voltage to 3.3. They do not effect the analog reference voltage. In fact the reason it is imperative that the AVCC be an extremely low impedance is because the frequencies involved are extremely high. All the VDD supply has to do is maintain enough voltage to keep gates of the Qs saturated. The AVCC supply is crucial because it has to absorb and source current at very high frequency and with very low noise at the same time.

Now it is important to bypass the VDD pins well (as I have done) but these pins are not in any way tied to the analog reference voltage.

The key to good results is a clean very low impedance AVCC supply.

I spent many many hours researching and testing this. And I have spoken directly with the kind folks from ESS on the optimal way to supply power to the chip. All of this research and advice has been put to good use.

So the bottom line is this. All of the supplies are important, and great care has been taken in evaluating the effects of decisions made and we made decisions that were optimal for the task at hand. The very most important aspect to each of the supplies is effective routing and bypassing. VDD is no different and we have taken very great care here.

This is one reason for the 4-layer board on the BUF-II. Initially we were convinced 2-layer would be sufficient, and it is just fine, but we have had much better results in terms of effective bypassing and routing with the 4-layer layout.

Nearly three years now I have been listening and tuning this DAC. I have been very diligent to understand how it works to the point where the kind folks at ESS have probably grown tired of all my questions.

Now please understand, I don't wish to disparage those who claim to have heard extreme changes in results by doing X instead of Y here, but I will tell you that I have yet to see such a claim that stands up to either logical or practical analysis. DIY people love to tweak, let them tweak all they want I say. But please understand, all of this has been gone over with extreme diligence.

Cheers!
Russ

[Duffy Moon]

It does make me chuckle when I see people asking Russ and Brian whether or not ripping out this capacitor or adding that capacitor or randomly adding distorting tubes hither and thither will improve the sound. Clearly if they thought it would, it would already be there.

I also consider it to be rather ill-mannered to tell Russ and Brian that you think their DAC does not sound good on their own forum and then ask why, or whether the next one will not sound so bad!

Anyway, I'm looking forward to receiving my IVY III and Buffalo II. Any idea when the documentation will be on the site by the way? I like to be prepared.

[glt]

Russ/Brian,

Q1: How is the analog reg daughter board attached? with headers and pins?
Q2: Don't you need some bypass caps at the inputs of the analog reg daughter board?