Hybrid Tube AMP/DAC for Raspberry Pi

The HifiBerry DIGI+ has the transformer out, but not the rest. Send me an email with a block diagram ([email protected]) and I'll put it together. I think I get what you're after, but just to be sure the block diagram will help. I can isolate the I2S bus and put the WM8804 on the isolated side and also allow external 5V in. Just 5V would be enough as I would use a low noise LDO to get 3V from the 5V.

Regarding clocks, we would need to put the Pi in clock slave mode and we'd use the NDK 2520SD series with a mux to select 24.576Mhz (48KH/96Khz/192Khz) or 22.5792Mhz. There would need to be some SW, but I think we can fork off of the Digi+ code since it's pretty similar.

Probably will take about 4-5 weeks to get PCB's back and build them up. I assume you'd test them? ;-) Any idea on price this should be? The Digi+ is $40, but does not have the isolation.

 

I'd be interested in that piece as well. I know nothing about diagrams but would definitely consider a purchase if you brought it to market.

 

Considering that some people pay $1000+ just to get a signal from PC to a DAC, you could charge quite a bit. That said, since the Pi is supposed to be the backbone of a reasonably priced system, I'd pay up to $99 for it, if the hat plus a Pi really ended up being a better transport than my computer.

 

Thanks for the opennes. I am not able to draw a block diagram. Basically what I'm after is an audiophile friendly Digi+. Standard digi+ plus is amazing... but I suspect it is underimplemented to keep prices low.
Is it possible or useful to implement a double clock for 44.1\48 khz multiples?

I agree with fraggler... people pay crazy money today for transport, but we have to consider that in the end it is a Pi HAT. I think people would happily pay 99usd for the pimped digi+
I'd be very glad to test it.

 

OK, let me work on this and get to you guys in a day or so. The one issue that pops up is we need to put the Pi I2S bus in slave mode so we can supply the clocks from the WM8804. Feeding the WM8804 from a pair of NDK 2520SD crystals (24.576Mhz and 22.5792Mhz) should give us very low noise clocking. To get the Pi into slave mode and perfofrm the proper clock selection, requires software. Not complicated but then we have to integrate that into the major audio platforms such as Volumio, Openelec and Rune Audio. It looks like there is already support for the Digi+, but I don't know how close we will be.

Thanks guys - this is what makes engineering fun!

 

It would be better if it worked out of the box without having to do OS modifications on the user side to adapt the software. Using digi+ driver would be better since it is widely supported, but obviously I know nothing about engineering so I might be saying utter nonsense. I'm just hoping that as a user.
Keep us posted, please.

 

Quick update - We just received the second revision PCB's and will be building them early next week. If you want to get on the mailing list you can do that at http://www.pi2design.com. We will be offering the units at the $99 on Kickstarter, but limited to the first 100. Those on the mailing list will be informed when the Kickstarter opens, which will be 24 hours before we announce it publicly.


Cheers,
Michael

 

Very interested in this! I am a big Raspberry Pi fan and I have the original Rev 1 board, the Pi B+, Pi2, Pi3 and Pi Zero. I have various DACs from HifiBerry that I play around with and I never expected to see a PiHat with a tube amp! I have no idea how you guys would market this though since this needs to appeal to an intersection of audiophiles (small) and linux enthusiasts (also small). Even so, I hope it sounds as good as promised and that you guys are successful.

HiFiberry makes one and has pins that can accept external power. I have it but I have yet to implement it yet. I have heard good things about using it with external power though. In the long term I plan on feeding this to a Schiit Gungnir which reclocks everything so I don't know how important that is.

Edit: I've been scooped. Although you might be interested in the DAC+ Pro version which has low jitter clocks and takes external power.

https://www.hifiberry.com/dacplus/

 

@Cspirou
The hifiberry digi can take external power but it shares it with the raspberry. Furthermore it pass the 5v to the raspy but takes the the 3volt from it, which is not ideal since the regulator onboard is a switching one, and they share the GND. It has only a clock for all sampling frequencies. Good for the price, but far from ideal.

Dac+pro has external power (it is the bare minimum to separate the raspberry from the analog section) but it has to be modified. I believe the most part of us would like to use the dac we have chosen, though I read that the dac+pro has made a lot of people happy.

Trust me, gungnir digital section is not a cure for all digital evil. I had the gungnir multi at home for some time and a good transport still matters, actually it matters even more if you want to see what a worthy dac is capable of.

 

I started a new thread for this project. It's over in 'Digital: DACs, USB converters, decrapifiers' under the clever name of 'Raspberry Pi I2S to SPDIF Hat'.

Many thanks to you guys for spurring this. And it won't be $1K or even $500! Heck, not even $99. Most likely just in the $50 range. I believe in charging based on cost with a decent margin. Obviously cost is more than just parts (assembly time, software, testing, etc), but no way I could live with myself charging 10x or more what it cost to make! Besides, I am standing on the shoulders of others. It's not like I invented this stuff!

Cheers,
Michael

 

Quick question - Does anyone have interest in SPDIF in? The WM8004 has a SPDIF input that I am currently not using. If so, would Coax or Optical be more useful? Or both? With Coax what research I did seems to disagree as to whether or not it should be transformer isolated.

 

No particular interest here but if it doesn't harm the sound I can't see why not. What would be the required actions to switch from the raspberry to an external spdif source?

Yeah, not all people are sold on spdif transformer isolation...I am though. What is your opinion?
What were you thinking of using instead? A small coupling cap to break dc ground loops?

Edit - I just realized this is the hybrid tube hat thread and you were most likely referring to it and not to the 503spd1.

 

Michael:

Good luck on the Kickstarter campaign! I backed the project earlier today and stumbled onto this thread while looking for more details. [I was originally among your mSATA backers; spotted you over at kickingitforward.org]

Among my collection I have a IQaudIO Pi-DAC+ and the transformer version of the Hifiberry Digi+ (and some less notable cards), so I'm curious to hear how the Tube and [eventual] SPDIF cards stack up.

General Feedback: A version using the PCM5122 would be interesting (32-bit/384kHz); but would probably require a lot more work [PCM5102 has useful features baked in that PCM5122 doesn't].

 

Backed this as well. I am not expecting great things but I will be glad to be (pleasantly) surprised.

 

The PCM5102A has the same specs as the PCM5122, 112db SNR, 32-Bit up to 384Khz. What it lacks is software programability. The PCM5122A has some digital filters that can be enabled/disabled using software, where the PCM5102A has HW control pins to do that. PCM5122 also has a digital volume control, but you already have that in the player running on the Pi.

Thanks for the backing the tube amp!

Cheers,
Michael

 

In case it was not clear, the Kickstarter campaign for the 503HTA has begun. We waited a day to let the folks who signed up on our web site get first crack. Now everyone on this thread can get one. Later today we will go global with various google+ groups, the Raspberry Pi community and several web sites, blogs, etc. The Kickstarter page is:

https://www.kickstarter.com/projects/1815752970/hybrid-tube-amp-for-the-raspberry-pi

 

Quick update - new photos of 503HTA rev. 2 are on the Kickstarter page.

 

I see this project is featured on Make Magazine

http://makezine.com/2016/05/06/warm-tube-tone-is-just-what-the-raspberry-pi-has-always-been-missing/

One question, what volume control does it use?

 

We use an ALPS RK097 series, conductive plastic.

Cheers,
Michael