Hybrid Tube AMP/DAC for Raspberry Pi

Discussion in 'Product Announcements' started by Michael Kelly, Apr 22, 2016.

?

Max. price you would pay?

  1. $99

    43.5%
  2. $149

    30.4%
  3. $199

    17.4%
  4. Over $200

    8.7%
Multiple votes are allowed.
  1. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    We just finished testing the prototypes of our 503HTA. a small Hat size add-on. It connects to the PI I2S port. A PCM5102A DAC drives single 12AU7 tube gain stage with solid state Class-A output. It is designed to drive headphones from 32 to 300 ohm quite easily. The design is derived from the popular Bravo V2 architecture with all the modifications recommended such as: IRL510 Output Mosfet; Regulated Heater Voltage to reduce cross-talk; Adjustable Plate Bias for Tube Rollers; Nichicon MUSE Output Capacitors; and Jumper-able output impedance of 1.5, 32 and 100 ohm and switchable gain selection to match your headphones exactly.

    Made in the USA with all top quality components in our own manufacturing facility. We'll be offering a 1 year warranty.The 503HTA also has on-board regulators to power the HAT and the Pi from a single, 24V external supply. Here's some photos of the first prototype:

    [​IMG]

    [​IMG]

    [​IMG]

    We will be building 10 rev. P2 beta untis in about 3 weeks. We are interested in getting some into the hands of experienced tube enthusiasts. Our listening test and performance measurements show it is much better than any stock Bravo V2 and very similar to a Project Ember.

    I look forward to all your feedback, the good and the bad!
     
  2. Friday

    Friday Friend

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    First post here and it's a sales pitch? I mean, I get that you see this as a sort of contribution to the community but the least you could do was to introduce yourselves properly first, and maybe speak with an admin staff. People around here might not take to this too kindly.
     
  3. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I looked around, but found no other mechanism. I tried to get contact info for the staff members, but they are hidden. We would be more than happy to contribute, sponsor, advertise, etc. Are you the proper person to speak to?
     
  4. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Belated but here is the intro to me:

    I am a computer engineer, but I grew up on analog including tubes. First design was a 12AX7 FM transmitter when I was 10 (1967, yikes, I am so old). Started several companies, latest is Pi 2 Design where we do Raspberry Pi hats and shields. Lots of digital, but some audio. I played around with a Bravo V2 and modded it. Liked it enough that I figured I would marry the two together! We hope to do lot's more in this space, but also in stand aalone DAC/AMPS, tubes, solid state, etc. We are very open to supporting community projects with PCB's, complete assemblies, etc. If you have design you want us to build, and there is some interest in the community, we will do it gratis. Then you can buy it form us, or take the design materials and build it yourself. We definitely want to be good members here and pull our weight.

    Michael
     
  5. Friday

    Friday Friend

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    Nope, I just happened to be feeling nice enough to give you a heads-up, and also because you didn't seem like a complete dick. I'd recommend you have a look here: http://www.superbestaudiofriends.org/index.php?threads/must-read-seven-simple-guidelines.3/
     
  6. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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  7. purr1n

    purr1n Desire for betterer is endless.

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  8. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Update 4/21/2016 - We just finished testing with the 6922/6DJ8 tube from JJ electronics. Very good results, At low voltage output (<=2Vrms or 6V pk-pk) it has lower distortion than the 12AU7, but requires a higher plate bias voltage (16V versus 12.5V). This limits the headroom for higher impedance headphones that might need as much as 6Vrms (17V pk-pk). We are seeing that high impedance headphones (150 - 300) might be better served with the 12AU7, while the 6922/6DJ8 will provide lower distortion for lower impedance (32-50) headphones that don't need the large voltage swing.

    But, the beauty of the 503HTA is that you can adjust it to what is right for you! BTW, we have found the simplest way to optimize is to set the volume and gain to the highest volume you want for your chosen headphones, adjust the bias until it sounds bad, then back off a bit. Voila! Near perfect adjustment for your tube and headphone.

    Based on this testing it looks like we will be offering a choice of 6922/6DJ8 or 12AU7 as standard options.

    P.S. Also added my profile, sorry about the delay.
     
  9. songmic

    songmic Gear cycler East Asia edition

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    Is it for Raspberry Pi only or could it be used with, say, a regular laptop?
     
  10. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Friday
    Our upcoming XMOS board will allow the 503HTA to be connected to any computer. The 503HTA by itself is designed to attach to a PI
     
  11. BioniclePhile

    BioniclePhile The Terminal Man - Friend

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    I'd say a $150 price point would be acceptable, provided it sounds pretty close to a Modi2/Vali2 setup. Would you happen to have the Vali2 to compare it with? If not, you should definitely get one cause they're pretty cheap and most everyone says they're good, especially for the price. Plus, it'd give you a nice comparison for what else is in the price range you might be going for.
    And you'll have a feckin' cute Vali2.
     
  12. purr1n

    purr1n Desire for betterer is endless.

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    Was this based on listening tests or calculations? The high impedance Sennheisers get pretty damn loud already at 0.550Vrms. The reason I ask is because I much prefer the sound of the 6DJ8s, and if there isn't a probably with gain, I'd rather go that direction.
     
  13. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    It was based on both listening and measuring. We have a Rhode & Schwarz UPL analyzer to do the measurements and we did some headphone listening on a pair Sennheisr HD600's. But, as everyone here knows, there is no standard for listening tests! It's all about your music, your headphones, your ears, etc, etc. To us, that is the attractiveness of this architecture. Simple and easy adjustments to get the sound to your liking. At least we hope so! We'll offer a 30-day money back guarantee since not everyone will be able to find that "sweet spot".
     
  14. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    One more note, the HD600's we played around with have 97db sensitivity. To get to 110db SPL (which is really, really loud) you need 2.5Vrms. The HD650's on the other hand, have a 103db sensitivity which requires only 1.2Vrms. This is why we have gain, output impedance and bias point all adjustable. It may take a few minutes, but we feel like most everyone will be able to quickly zero in on the best sound for their setup.

    But, please understand, this is a simple, low voltage, triode gain stage with a Class-A MOSFET buffer. It is not the last word in tube amps or headphone amps in general. Just a single architecture that seems to be well received by you all.

    Cheers - Michael
     
  15. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    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.

    We're also looking for beta testers. We'd like to get the 503HTA supported under Volumio and RuneAudio. Others if you have a specific platform you are familiar with. We have a number of audio hats, including our upcoming 35W/Channel Class-D amp with headphone out, that we'll be needing testers for going forward.

    Cheers,
    Michael
     
  16. fraggler

    fraggler A Happy & Busy Life

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    Very interesting work. I am more interested in streaming to an external DAC/Amp for headphone listening, but could be very interested in the Class D hat for Sonos-like music distribution, but with better speakers.
     
  17. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    We have a headphone out on the Class-D hat. it uses the TI TAS5756 and uses a TPA6130A2 for headphone out. Good for driving low ohm headphones, not much above 32 ohm. Also in process is our 503HDA which uses the ES9018K2M Sabre DAC with an ultra-low headphone amp that can drive pretty much any headphone. We use the TPA6120A2 in that case with low noise +/- 15V supplies. Obviously a totally different animal than our Tube hat! So lots of choices for the Pi.
     
  18. fraggler

    fraggler A Happy & Busy Life

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    Why so many headphone oriented hats? I mean, if I had the engineering chops, I'd probably play with a lot of different configurations too, but from a commercial standpoint, is there that big a market for dac/amps built on top of the source/streamer? Speakers, definitely. I guess the Kickstarter campaign will provide the answers. Thanks for sharing your efforts with us.
     
  19. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I know it might seem a little crazy, but heck, there are massive forums dedicated to all things headphones, such as http://www.head-fi.org/f/. http://www.diyaudio.com/forums/headphone-systems/ has headphone amp threads approaching 1 million views and several thousand replies. OK, yeah it IS crazy!

    Also, there are in excess of 5 million Raspberry Pi B+, 2 and now 3's that all have horrible audio out. Even a pessimistic Venn diagram between the two camps means thousand of users looking to use the PI for headphones, and of course, all types of audio.
     
  20. Vastx

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    Speaking of all kind of audio I'd be very glad to buy a good I2S->spdif converter for the pi. But it would have to have decent clocks, coax isolation transformer and the possibility to feed it with isolated 5v and 3,3v (if needed) apart from the pi without cutting traces on the pcb. Think you'll do something like that in your road map?
     

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