Bottlehead DAC prototyping takes another step forward

[Doc B.]

I got some good news this morning that John Swenson has made significant headway on a central part of the DAC that he was struggling with this summer, the interface with the EEPROM that will allow the DAC to incorporate future firmware upgrades. If things continue to go well for him we may have a new prototype to work with soon that is much advanced over the one we have been demoing for the past year or so. I'm still not offering release dates or quoting prices as there is work left to be done that can't be started until we complete this stage. But I do want to share the most recent progress in the design development.

[denti alligator]

Great! So it's not being abandoned, then. That is great news!

[Jim R.]

Tuned in for any updates...

Glad there is progress!

-- Jim

[earwaxxer]

2nd that - any info would be great!

[grufti]

"..., the interface with the EEPROM that will allow the DAC to incorporate future firmware upgrades."

That sounds interesting. Do you plan on using FPGA's in your DAC?

[Doc B.]

Yes

[John Swenson]

There is an FPGA that is the heart and soul of this DAC, it pretty much does everything. It does the S/PDIF decoding, the USB decoding, all the work for the very low jitter adjustable clock that follows the S/PDIF data rate, output encoding, display drive, and pretty much everything else.

About 95% of this project has been coding the FPGA. Because the FPGA does pretty much everything I'm not stuck doing things the way a particular chip does things, BUT it means it does take time to program the FPGA to get it to do exactly what I want and sound the best.

Because it IS based on an FPGA, pretty much any part of it can be changed out in the field. The simplest way to add upgrades is to plug in a memory chip whose contents gets copied over into the FPGA configuration store. Making that work is what I have been working on all summer. The manufacturers of these chips seem to do everything in their power to make them complicated. I finally got it all up and running this week. I can now send DOC firmware upgrades on a little memory chip rather having him send it back to me for reprogramming. This will be a feature on all the production DACs so as we make improvements they can be incorporated in your DAC by just installing a new little memory chip.

I thought hard about using USB to download firmware files, but  that means we have to write software that runs on Windows, Macs, Linux and every version of these under the sun, and keep them maintained forever. Mailing out a little chip is just WAY easier! And since this is a kit, the users should not be afraid to open the lib and put in a new chip.

Now I have to build a version of this to send to DOC. I had two boards made, but I had to make a bunch of changes to the board to get this chip to FPGA copy thing to work. (it's amazing how much information is left off data sheets)

Anyway it definitely is NOT dead. I am working furiously try to get this done as soon as possible. This version I'm sending to DOC is very similar to what the final will be like. I it DOES sound amazing!

John S.

John S.

[2wo]

Great to hear. I was worried a while back, that the DAC had lost momentum and would be shelved.

I am still looking forward to it...John

[Wormwood]

Doc or JS - what will the final footprint be? Will it be akin to your other products or a totally different form factor?




Wormwood

[denti alligator]

This is very exciting! Are we looking at so something for as soon as early next year?

[earwaxxer]

Is the dac going to use tube output, or will it be driven by chips, Jfets, opamps?

[John Swenson]

I can pretty much guarantee that there will be a tube output stage of some sort. That's one of the things still under development.

As far as I know its going to look similar to other Bottlehead products, with the wood base and metal top plate with everything connected to the top plate. The current thinking is that the board I am designing (which has all the chips etc) will hang down underneath the top plate with its own aluminum housing for shielding purposes. (primarily to keep the digital noise out of the tube circuits!) All the digital input jacks are mounted on the board and stick up through the top plate. There is an edge connector on the board and a slot in the top plate for inserting a display baord which will have some form of sample rate display and lock detect etc. This makes it very easy to add other display options such as my favorite, a Nixie tube display!

This edge connector is also an interface for attaching additional input options and connections as time goes along.

The rest of the box will contain the tube circuit and the power supplies similar to existing Bottlehead products I presume.

As to schedule, thats a toughy, there is still a lot of work to do, I can guarantee at least one more prototype will be needed (I'm working on that already).

Then once we get a prototype working Doc and company have to make it into a kit, THAT part I don't have any insight into.


I know you want a date, but as of right now I can't give that.


John S

[Wormwood]

JS,

Thanks for the overview. The Nixie tube display I have seen but never really chased before but to think with that on the plate it would look awesome... and looks do count!


Wormwood

[John Swenson]

I love Nixie Tubes, growing up in the early sixties my dad used to design all kinds of equipment with Nixie Tube displays, I would get hooked just staring at these things for a long time. About 8 years ago I built a Nixie clock, I have it on my mantle in the listening room and love to watch the thing count when I have the lights down dim listening to good music.

John S.

[Wormwood]

Would you be able to point me in a how-to-build a Nixie Clock site.

Sorry for going OT.


Wormwood