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Neurochrome HP-2 ultra-low distortion headphone amplifier
Neurochrome HP-2 ultra-low distortion headphone amplifier
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Old 9th November 2019, 07:25 PM   #1
tomchr is offline tomchr  Canada
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Arrow Neurochrome HP-2 ultra-low distortion headphone amplifier

World, I present to you the All-DIY Neurochrome HP-2 ultra-low distortion headphone amp.

I will be demoing it tomorrow (Sunday Nov. 10, 2019) at the Burning Amp Fest at Ft. Mason. If you're in San Francisco, please stop by for a demo and chat.

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 V 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!).

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.

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). You can buy your HP-2 here: Neurochrome HP-2.

Thanks,

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 9th November 2019 at 07:56 PM.
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Old 9th November 2019, 07:28 PM   #2
poseidonsvoice is online now poseidonsvoice  United States
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Neurochrome HP-2 ultra-low distortion headphone amplifier
Superb! Can’t wait to listen to it!

Best,
Anand.
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Old 12th November 2019, 12:03 AM   #3
spikestabber is offline spikestabber  Canada
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Measures better than a "The Wire BAL-BAL", but given the transparency of the BAL-BAL already I doubt I would ever notice a difference with existing direct coupled HD800.

One area I would suggest in the next version is a true differential output, many who would spend that much for a HP amp would already have an existing 4 pin rig.
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Old 12th November 2019, 12:57 AM   #4
tomchr is offline tomchr  Canada
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You can build the HP-2 with the following outputs:
  • 1/4" phone connector
  • 3.5 mm phone connector
  • 4-pin XLR connector
Naturally, fitting the amp with a 4-pin connector does not make the amp balanced, but it does interface nicely with phones that use such a connector.

There's only a minuscule benefit of using the 4-pin connector. You get ever so slightly better channel separation as you do not have the shared ground connection in the 4-pin connector.
Some will argue that a balanced amp will provide lower distortion due to the cancellation of harmonics. That's true in a high-distortion design. The cancellation doesn't work well for low-distortion amplifiers. In fact, any sort of cancellation scheme is much more likely to degrade the performance of a low-distortion amp than to improve it. Even in the cases where the THD is reduced by such cancellation, the cancellation mostly affects the even order harmonics the ones most find pleasant sounding while leaving the odd order harmonics (that many find to sound harsh) in place.

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 12th November 2019, 10:55 AM   #5
RickTH is offline RickTH
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No block diagram (yet) on your site, like the HP1 .
HP-2 – Neurochrome

How do you go from the 28Vdc to a + and - supply ?
It's LME49720 + 2 paralleled OPA1656 with an AC coupled output, so a capacitor at the output . mmm...
Output Impedance 2.6 Ω ? Pretty high...
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File Type: png HP1 block diagram.png (64.9 KB, 127 views)
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Old 12th November 2019, 06:42 PM   #6
BrianL is offline BrianL  United States
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Neurochrome HP-2 ultra-low distortion headphone amplifier
You would be speculating based on no data?
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Old 14th November 2019, 08:47 AM   #7
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by RickTH View Post
No block diagram (yet) on your site, like the HP1 .
Correct. I need to proofread about half the verbiage as well. 24 hours/day one person kinda thing. I just got caught up after returning from BAF.

Quote:
Originally Posted by RickTH View Post
How do you go from the 28Vdc to a + and - supply ?
I don't. Hence, the output cap. I use nested feedback to eliminate the THD of the output cap. It works rather well.

Quote:
Originally Posted by RickTH View Post
Output Impedance 2.6 Ω ? Pretty high...
Meh... Does it matter? I agree that it won't look as good on Amir's ranking plots on Audio Science Review, but it will certainly work well (as my data show).

Tom
__________________
Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 21st November 2019, 11:02 PM   #8
tomchr is offline tomchr  Canada
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And now... A block diagram.

I have one PCB left at the intro price.

Tom
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File Type: png HP-2_BlockDiagram.png (142.9 KB, 78 views)
__________________
Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 22nd November 2019, 12:45 AM   #9
spiggs is offline spiggs  United States
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Would there be any issues using HP-2 as a preamp as well?
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Old 22nd November 2019, 01:10 AM   #10
tomchr is offline tomchr  Canada
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That will be fine. If you use a switched output connector, you can just take the preamp output on the switched side. That way, the preamp out is turned off when you plug in the headphones.

Tom
__________________
Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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