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Neurochrome HP-1: Ultra-High End Headphone Amp
Neurochrome HP-1: Ultra-High End Headphone Amp
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Old 10th December 2016, 05:47 AM   #1
bazelio is offline bazelio  United States
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Default Neurochrome HP-1: Ultra-High End Headphone Amp

I thought I'd start a thread dedicated to the new headphone amp design by Tom Christiansen (Neurochrome). This can be ordered pre-built, or as a partial-DIY project where Neurochrome supplies the PCB, chassis, and BOM list. I'd caught wind of this amp a while back, and preordered the PCB from Neurochrome before manufacturing had completed. Now that Tom has notified me that boards are shipping imminently, I thought I'd get this thread started.

Full specs for the Neurochrome HP-1 are available here. Tom seems to have set out to produce the ultimate "wire with gain" in the HP-1, delivering 3W/20Ω, 450mW/300Ω @ 0.000032% THD! He's using the OPA1612 differential receiver and LME49600 output stage in a loop with an OPA1611.

I've never heard this headphone amp, so am taking a flier on it based solely on my admiration for Tom's circuit design skills. It has also been quite a long while since I've done any SMD soldering, so it'll be a fun project. I'll post some pics of the build as I go and listening impressions at project completion. Meanwhile, my box o' Mouser BOM parts is ready to go!

BTW, this proto unit built by Tom is also going to be making the rounds in the US among some hobbyists. And it has been auditioned up in Canada at a local Head-Fi meet, from what I understand:

Click the image to open in full size.

Last edited by bazelio; 10th December 2016 at 05:57 AM.
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Old 10th December 2016, 05:48 AM   #2
bazelio is offline bazelio  United States
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Old 10th December 2016, 05:52 AM   #3
bazelio is offline bazelio  United States
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Old 10th December 2016, 06:39 AM   #4
tomchr is offline tomchr  Canada
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Fantastic! Thank you for starting a build thread. I appreciate it. I'm looking forward to watching your progress.

The board and chassis bits will be underway by Monday and should reach you before Christmas. What you're getting is actually a bit of a "one of a kind" kinda thing. Well. The second of a kind. You'll get the latest board revision, Rev. 1.1 with the black chassis. Future chassis will be blue (RAL5010 Genetian Blue to be specific). The texture will be the same.

As you point out, the goal of the HP-1 was to go directly for the high end. 3 W into 20 Ω, 1.0 uV noise floor, sub 1 ppm level THD. Added protection circuits to protect your headphones.

The HP-1 uses the OPA1612 for the input buffer, OPA1611 + LME49600 (with appropriate compensation) for the output drive, and an OPA2140 for the DC servo. All signal switching is done by Kemet relays with gold plated switch contacts.

There's a bit of chatter about the HP-1 on SBAF. It seems it's been discovered on Head-Fi as well, with a listening impression here: Amps that can drive the HiFiMan HE-6.

So far, I have demoed the HP-1 at the Calgary Head-Fi meet back in October and about two weeks later at a local hifi store, The Audio Room, which hosted a Focal headphone event. Two reps from Focal were there and were quite impressed with my amp. It performed really really well with the Focal Utopia. Man... The amp then went to Winnipeg where it was demoed at a Head-Fi meet there. The first prototype is currently underway to Washington DC and will be on a demo tour (arranged through SBAF) across the country until it lands with its final owner in California.

So far, I've heard it with:
  • Focal Utopia
  • Focal Elear
  • Sennheiser HD-650
  • Sennheiser HD-600
  • Sennheiser HD-580
  • HIFIMAN HE6
  • HIFIMAN HE1000
  • HIFIMAN HE560
  • Etymotic ER-4 (IEM)
I'm liking it!

Tom
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Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 10th December 2016 at 06:53 AM.
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Old 10th December 2016, 08:50 AM   #5
sq225917 is offline sq225917  United Kingdom
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Send a message via MSN to sq225917 Neurochrome HP-1: Ultra-High End Headphone Amp
Headfi, the ultimate snake's den of competing commercial interests and secret back room deals. I find the place about as trust worthy as Steve's mastering forum.

Good luck with the design tom, it appears right on the money spec wise.
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Old 10th December 2016, 10:05 PM   #6
tomchr is offline tomchr  Canada
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Yeah I much prefer the atmosphere here.

Tom
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Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 15th December 2016, 05:40 PM   #7
tomchr is offline tomchr  Canada
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The FFT plots showing the 1 kHz THD show a bunch of harmonics at multiples of 30 Hz. That is due to a ground issue in the precision oscillator I'm using (Victor's oscillator).

The best graph to see the residual mains hum under load is the multi-tone IMD graph. It shows the tallest mains harmonic (300 Hz) at -120 dBV.

The residual mains hum plot showing < -136 dBV was done with the inputs shorted, output loaded with 300 Ω.

I'm not seeing the -137 dB (no reference) you mention. All the dBs say dBV. What am I missing? You're looking at this page (HP-1: Ultra-High End Headphone Amplifier), right?

Tom
__________________
Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 15th December 2016, 06:00 PM   #8
Gopher is offline Gopher  United Kingdom
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Just ignore my ramblings, must be too tired. Sorry. Are those two peaks at -95 dBV and -100 dBV around 60 Hz on the 200 mW into 300 ohms and 32 ohms graphs the oscillator or real mains hum? they seem to be distinct from the 30 Hz peak train.

Last edited by Gopher; 15th December 2016 at 06:05 PM.
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Old 15th December 2016, 06:09 PM   #9
tomchr is offline tomchr  Canada
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I'm 99.99 % certain they're related to the Victor oscillator and its supply. They go away when I use the AP's oscillator, but the oscillator in the AP is "only" good to -112 dB THD at its sweet spot. Victor's goes to <-140 dB THD.

Tom
__________________
Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 15th December 2016 at 06:11 PM.
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Old 15th December 2016, 06:12 PM   #10
Gopher is offline Gopher  United Kingdom
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Just out of interest did you look at the new OPA 1622 or OPA 1688 before you settled on your choice of op-amps? They look pretty impressive for headphone applications.
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