Neurochrome HP-2 All-DIY Low-Distortion Headphone Amp

Discussion in 'DIY' started by tomchr, Nov 14, 2019.

  1. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    Fellahs,

    I present to you the Neurochrome HP-2 All-DIY Low-Distortion Headphone Amplifier.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    Key features of the HP-2:
    • 4-layer PCB fully optimized for performance while being relatively easy to assemble.
    • Output power: 440 mW (32 Ω), 660 mW (50 Ω), 260 mW (300 Ω) at vanishingly low distortion.
    • Inputs: Balanced/differential (XLR) and unbalanced/single-ended (RCA).
    • Alps "Blue Velvet" volume potentiometer.
    • +5 dB and +15 dB gain settings (jumper selectable).
    • Integrated headphone protection circuit, which disconnects your headphones in the case of DC voltage on the output of the amplifier.
    • Integrated output muting circuit ensures that the HP-2 is completely absent of turn-on and turn-off clicks and pops.
    • Optimized on-board RLC power supply filter allowing for stellar performance with the recommended switching power supply.
    • External 28 VDC switching power supply accepting 85 – 264 VAC mains for use world wide.
    • The PCB features elaborate use of planes and copper pours to maximize circuit performance by minimizing supply and ground impedances.
    • On-board EMI/RFI input filter to prevent wifi and switch transients from interfering with the sound reproduction.
    • With the exception of two SOIC-08 surface mounted ICs, the HP-2 is all through-hole construction with socketed ICs and is easy to solder.
    • Bill-of-materials includes a Mouser Electronics Project Link for ease of parts ordering.
    • Gold plated PCB, fully electrically tested by the manufacturer.
    • PCB is designed and manufactured in Canada.
    • Custom designed chassis manufactured in Italy.

    Build budget:
    • Cost of parts for the PCB: ~$160 (including power supply)
    • Cost of a full build using my custom chassis: ~$500

    Spec. highlights:
    • Output power: 440 mW (32 Ω); 660 mW (50 Ω); 260 mW (300 Ω)
    • THD: < -130 dBc (50 mW, 300 Ω)
    • Multi-tone IMD residual: -144 dBr (AP 32-tone, ref. 100 mW, 300 Ω)
    • Output noise: 1.0 µV RMS (A-wt, 20 Hz - 20 kHz)
    • Dynamic range: 125 dB
    • Gain: +5 dB, +15 dB (jumper selectable)
    • Input sensitivity: 2.90 V, 865 mW (gains +5 dB, +15 dB, respectively; 100 mW, 300 Ω)

    You can find the circuit description and full specifications on my website: Neurochrome HP-2.

    But, but... What does it sound like? I like it, obviously. Ever since I heard my first precision amp, I've been hooked on the precise (i.e. ultra-low distortion) sound. I prefer that the amp makes as little contribution to the sound as possible, as I believe this allows for experiencing the music the way the artist and recording engineers intended it. The precision of the HP-2 allows it to provide realistic and natural rendition of the source material, with a wide and open sound stage (even in headphones!).
    I presented the HP-2 at Burning Amp last weekend and many commended it for its tight bass control and precise rendition.
    That said, some prefer their headphone amps to add a little grunge, distortion, or cross-feed. That's fine. We don't all have to like the same stuff. However, if you prefer the amp to add a li'l something-something to the sound, you'll probably find the HP-2 lacking.

    The HP-2 will only be available as a DIY product, i.e. I will not be offering it in a fully assembled option. The PCB features two surface mounted components. They're relatively easy to solder 8-pin SOICs. Should you wish to have me solder those ICs for you, I can do that for a small fee.
    In addition to the PCB, I offer a nice aluminum chassis, which has been custom designed for the HP-2. The chassis is a very nice option for DIYers who would like to showcase their builds in the form of a professional-looking product. Before you balk at the chassis cost, beware that if you were to order the chassis at QTY = 1 directly from the manufacturer, it would set you back over $250 + shipping due to all the modifications (holes, millwork, digital printing, etc.)

    I am offering the HP-2 at pre-order prices until they arrive in stock or until the first ten HP-2s have sold (whichever occurs first). The PCBs went into production today and should be here by the end of November. You can buy your HP-2 here: Neurochrome HP-2.

    Thanks,

    Tom
     
    • Like / Agree Like / Agree x 17
    • List
  2. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

    Friend
    Joined:
    Sep 28, 2015
    Likes Received:
    3,750
    Trophy Points:
    113
    Where did all the heatsinked transistors go?
     
  3. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    They didn't provide the performance I wanted, so I found a different solution. That also reduced the board size rather dramatically, which made it possible for me to sell it at the current prices.

    Tom
     
    • Like / Agree Like / Agree x 1
    • List
  4. Joshvar

    Joshvar Facebook Friend

    Contributor
    Joined:
    Mar 22, 2017
    Likes Received:
    134
    Trophy Points:
    33
    Location:
    Austin, TX
    Any requirements/concern with using an LPS with the HP2 for those of us with one lying around?
     
  5. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    LPS? Linear power supply? I see no issue with those. I recommend using a regulated supply in the 15-30 V range. Higher is better. It'll need to be able to supply min. 500 mA. The switching supply I recommend is a 28 V, 890 mA type.

    At lower supply voltages, you'll get lower output power. The amp should run just fine on an old laptop charger. They tend to be around 19-20 V these days.

    Tom
     
    • Like / Agree Like / Agree x 1
    • List
  6. bluebyte60

    bluebyte60 Rando

    Contributor
    Joined:
    Jun 12, 2017
    Likes Received:
    64
    Trophy Points:
    13
    Location:
    Sunnyvale, CA
    @tomchr, just a random curious question, when you made the gain switchable, I imagined we can use some sort of mechanical switch to change the gain too. Why not providing the drill hole on the front panel ? I think it's kind of popular and usable feature :).
     
  7. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    I agree that providing a gain switch would make some sense. On the other hand, I wonder how many change the gain once they've found a gain setting that provides enough volume in their headphones. Many headphone amps don't offer gain options at all and seem to be doing just fine. In the design doc, I will provide the gain equation and a list of resistor values for various gain settings. That should allow builders to tweak the gain to their preferred value.
    The component density on the board is pretty high. I'm sure I could have tweaked, rejiggered, and scooted things around to fit in the gain switch, but I opted not to. The HP-2 is a DIY project so many will build it into their own chassis and can add knobs and switches to their heart's content.

    Also - to be completely honest here - I don't want the HP-2 to be competing with my commercial offerings, such as the HPA-1: www.tomchr.com, so having it be more DIY and less "finished product" makes sense from a marketing and positioning perspective.

    Tom
     
    • Like / Agree Like / Agree x 2
    • List
  8. gepardcv

    gepardcv Almost "Made"

    Contributor
    Joined:
    Nov 20, 2015
    Likes Received:
    347
    Trophy Points:
    63
    Location:
    Terra, Sol System
    Out of curiosity, what's the performance difference between the HP-1 and the HPA-1? I see it has no XLR output socket, but what else is going on with the new amp?

    Edit: Similar question, I guess, for the HP-2 and the HPA-1. Seems like the HP-2 has somewhat lower output power, and uses an external PSU. Anything else?
     
    • Like / Agree Like / Agree x 2
    • List
  9. Tristan Jones

    Tristan Jones Rando

    Joined:
    May 6, 2018
    Likes Received:
    58
    Trophy Points:
    13
    Location:
    Seattle
    But tom, where are the 300bs?
     
  10. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    By coincidence, I answered a very similar question on ASR recently. Please allow my blatant reuse of that answer:
    • The Neurochrome HP-1 (now discontinued) was a DIY headphone amp. Many requested it fully built, which is how this thread came into existence.
    • The Neurochrome HP-2 (just launched) is a DIY headphone amp. It will not be available as an assembled product. Ever. Not assembled by me anyway. If you can find someone to assemble it for you, great! The HP-2 provides about the same performance as the HP-1 with high-impedance loads. It provides slightly worse performance into low-impedance loads. It also provides much lower output power into low-impedance loads. Those were the tradeoffs I had to make to make the amp all-DIY (and not compete with my TCA products). The HP-2 is currently on into special. The first 10 buyers will save 10%. You can find more information about the HP-2 here: https://neurochrome.com/products/hp-2
    • The Tom Christiansen Audio (TCA) HPA-1 is a retail headphone amp. It will never be available as a DIY product. It has been optimized for low-volume mass production (batches of 100-250 amps at a time). My intent was to keep as much of the HP-1 performance as possible while making the amp mass-producible. This required a drastic reduction in BOM cost, and it required the design of a chassis and volume control that provided a better user experience. I was able to meet or exceed many of the HP-1 specs, but I had to trade off some output power. The Neurochrome HP-1 provided 3 W into 32 Ω, the TCA HPA-1 provides 1 W into 32 Ω. Many want 5 W for their planar headphones and neither amp would satisfy those needs. I would also invite those who believe they need 5 W into a headphone to reevaluate need vs want. You can read more about the TCA HPA-1 here: https://www.tomchr.com/products/hpa-1 Note that the first 40 of these are on early-bird special ($649). I've sold 20 of them while hardly doing any advertising. The chassis is in production and the PCBs will go into production by Wednesday. I expect to be able to ship the amps starting around December 20th. At that time (or when 40 amps have sold), the price will go up to $899. You can see the AP test report (with graphs) of the prototype build on the "specifications" tab. I will add all the plots on a "performance graphs" tab once I get the first production batch in. Expect the graphs to show in early December. I will also send a sample to Amir for review.
    Some may wonder about all this TCA vs Neurochrome stuff. So here's the deal: DIY is by many perceived as cheap. It turns out it's hard to command a good price for a premium product if your brand is perceived as cheap. Thus, I launched TCA as my retail brand. There are other factors in play as well:
    • I increasingly find myself hamstrung with my DIY designs. From my past experience, supporting builds that use surface mounted parts is a nightmare. Using only leaded parts degrades performance as I don't have accesses to the higher performing parts, and it drives up cost as the PCB area grows significantly when leaded parts are used. Thus, expect my Neurochrome products to provide lower performance than my TCA products.
    • With my TCA retail designs, all options are open, which allows me to optimize for performance. The main challenge there is to keep the cost under control. Distributors generally take about 30-40% commission. If I use an agent or representative to get in with that distributor, there goes another 5-6%. I need to eat periodically, so I need to keep my margins up in order to survive. That said, I think I can bring to market some very high-performance products at a quite reasonable price.
    In above, the term "performance" refers to the measured performance below clipping. In terms of sound quality (subjective performance), I generally find that with high-impedance headphones (Sennheiser HD-650, for example), at reasonable volume levels, I have a very hard time telling the amps apart. I do find that with phones that are a little harder to drive (even my 80 Ω Focal Elex), the higher powered amps (HP-1, HPA-1) stand out against lower powered amps (HP-2 and an OPA1622-based design I tinkered with a while back).

    Yeah... No light bulbs for you! :) There were a couple of reasons for why I decided to let the DG300B go:
    • Every build is different, which means that nearly every build needs considerable support. I do enjoy providing that support, but it takes a lot of time, so at some point I have to start thinking about the opportunity cost. I could be doing something else with that time, that would be more likely to result in increased revenue.
    • The last year before I discontinued the DG300B, I sold about ten board sets. This means even a small stack of boards would take 2-3 years to turn. This became a problem when Omron decided to change the footprint for one of the relays used in the power supply. I had to throw away quite a few boards ($$$ in opportunity cost) because the relay would no longer fit and there was no replacement.
    • Interestingly, it was a comment by someone here that provided the last straw. This person very aptly pointed out the inconsistency of having a 300B design while at the same time pushing a message of good measurements == good sound (which I firmly believe). Suddenly the clue light went on for me. I'd never thought about it that way, but wholeheartedly agreed. So I cleaned up my messaging by getting rid of the tube designs.
    So in summary: High cost of support + slow sales + inconsistent message -> no more DG300B (or Novar Spud for that matter).

    Tom
     
    • Like / Agree Like / Agree x 5
    • List
  11. gepardcv

    gepardcv Almost "Made"

    Contributor
    Joined:
    Nov 20, 2015
    Likes Received:
    347
    Trophy Points:
    63
    Location:
    Terra, Sol System
    Thanks for the info.

    Something in your comment caught my eye: “every build needs considerable support”. Is this true for the HP-1 and HP-2 as well as the 300B? Is that part of the reason for the fairly high prices for bare Neurochrome PCBs? For comparison, I paid $250 for a set of Gilmore DIY-T2 boards, but they’re absolutely gigantic with 4oz copper and it was a tiny (group buy of 5 people) run. The HP-2 has a much much smaller board, presumably a much larger run, and yet costs $200.

    For background: I was slightly intrigued by the HP-1 when it was available, but the PCB cost turned me off. Now I’m even more interested since all the good feedback came out recently, but no more boards are available, and $200 still seems like a lot for a bare board, something which will likely require a couple dozen hours of DIY work and a few hundred dollars in parts and casework.
     
    Last edited: Nov 21, 2019
  12. Hands

    Hands Overzealous Auto Flusher - Measurbator

    Staff Member Friend MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    11,782
    Trophy Points:
    113
    Location:
    Colorado
    Home Page:
    Thanks to its extremely low intermodulation distortion – in particular on multi-tone tests – the HPA-1 renders the music with an incredible realism and an amazing sound stage without resulting in listening fatigue.

    Ah, yes, I remember how fatiguing the first gen Metrum DACs were.

    The "sappy verbiage" you rail on has another side on the coin. You know this, right?
     
  13. purr1n

    purr1n Finding his inner redneck

    Staff Member Friend BWC
    Joined:
    Sep 24, 2015
    Likes Received:
    73,800
    Trophy Points:
    113
    Location:
    Padre Island CC TX
    FWIW, toob amps (known for soundstage and "listenability") fail at IMD and multitone tests - we talking about "grass" city here. Low IMD has no correlation with amazing soundstage and no listening fatigue.
     
    • Like / Agree Like / Agree x 4
    • List
    Last edited: Nov 21, 2019
  14. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    I was writing about the 300B. The support was mostly related to tube options, output transformer options, and power transformer options. Solid state builds require much less support.

    Compared to the performance you're getting, the prices are quite low. If you want cheap, shop on eBay. You'll get zero support and often not even a parts list. Best of luck. ;)

    The HP-2 circuit board is $99.

    The chassis is $199. That's actually below cost. If you were to buy the chassis at QTY = 1, you'd pay over $250 due to all the machining and digital printing. I bought 25 of them and am passing part of the bulk discount onto you.

    I'm not sure where you get those prices from. If you would rather buy a finished product, you can always have a look at my TCA HPA-1.

    Tom
     
  15. Tristan Jones

    Tristan Jones Rando

    Joined:
    May 6, 2018
    Likes Received:
    58
    Trophy Points:
    13
    Location:
    Seattle
    I was just playing around with you :p.

    But thank you for the detailed response.

    I am very surprised the DG300b didn't sell better. Those amps were around when I was just getting into audio and I always enjoyed seeing shiny glowy 300bs at audio meets. Sad to see it go.
     
  16. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    Yeah... Opamps have a really hard time replacing the warm glow of a mesh plate 300B. That's for sure. :)

    Tom
     
  17. Baten

    Baten Friend

    Friend
    Joined:
    Mar 18, 2018
    Likes Received:
    881
    Trophy Points:
    93
    Location:
    EU
    Looking good. Any update @tomchr ?

    PS It's a pity neither HPA1/2 have an XLR output (even if it was SE, just for convenience).
     
  18. tomchr

    tomchr MOT - Neurochrome

    Joined:
    Oct 28, 2016
    Likes Received:
    515
    Trophy Points:
    93
    Location:
    Calgary, Canada
    Home Page:
    Yep. As of 2pm this afternoon, the HP-2 PCBs (both options) and the chassis are now in stock. All preorders have shipped.

    You can build the HP-2 with 4-pin XLR if you wish. In the design doc, I give the relevant part numbers for 1/4", 3.5 mm, and 4-pin XLR connectors that will fit the chassis.

    Tom
     
    • Like / Agree Like / Agree x 1
    • List
  19. bluebyte60

    bluebyte60 Rando

    Contributor
    Joined:
    Jun 12, 2017
    Likes Received:
    64
    Trophy Points:
    13
    Location:
    Sunnyvale, CA
    Just ordered a bare pcb board. I bought a high voltage regulator module from @tomchr before, I am very impressed by documentation and the product itself. The document is very detailed and easy to read for a ok diyer like me. Although currently have no time to build anything, but can still do some planning ahead. @tomchr will you recommend any linear power supply module? You did mention switching power supply. but my empty chassis already have IEC socket drilled. Do you have any recommend transformer and ac -> dc module in mind? The smaller the size the more I like :D
     
    Last edited: Feb 29, 2020
  20. kris2014

    kris2014 Acquaintance

    Banned Contributor
    Joined:
    Feb 1, 2020
    Likes Received:
    37
    Trophy Points:
    18
    Location:
    us
    Mine is almost complete. I am still waiting for power switches and HP jack to arrive. So many parts are out of stock lately, especially the bourns fb20020. I ordered fb20011 3b and cut the extra pair of leads I don’t use here. I later used those leads to have tkd pot anchored to the daughter board. I will run tests and sand the chasis a bit for better groudning over the weekend. Hopefully everything will arrive soon.

    Bear with my soldering skills. I hope it is not eye burning.

    [​IMG]
     
    • Like / Agree Like / Agree x 3
    • List

Share This Page