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Review and Measurements of Neurochrome HP-1 High-Performance Amp

kn0ppers

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That is probably a good idea. Better safe than sorry.

Nichicon Muse capacitors...for DC blocking or something like that? Do you believe in "audiophile" capacitors or what made you choose them? I mean they sure look nice ;)
 
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amirm

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I'm actually not the one doing the design. A friend of mine is a graphic designer. I'm having him help. I don't want to burn too many CPU cycles with him, so I just hacked a version with closed ends in Photoshop:
View attachment 31729

Tom
Like this version better too.
 

tomchr

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Nichicon Muse capacitors...for DC blocking or something like that? Do you believe in "audiophile" capacitors or what made you choose them? I mean they sure look nice ;)
I believe in science and engineering. The capacitors I use cause no measurable degradation of of the audio signal. Many so-called "audiophile" capacitors measure significantly worse than regular off-the-shelf components. What "audiophile" components seem to do really well is drain your wallet. If you want good performance, just shop at Digikey or Mouser.

Tom
 

maxxevv

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HPA-1 prototype assembled. I still can't measure its THD. My precision oscillator 'only' gets me to -128 dB or so. The amp's THD is below that (1 V RMS into 300 Ω).
View attachment 30924

Tom

That looks neat and tidy.

Let me know if you need help in designing a fancy machined case for it. :p:D;)
 

tomchr

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Thank you. The chassis should ship early next week. Yay...

Tom
 

The Mule

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Hi. Tom - I like the 2nd version too. :) Have you tried not all caps for the text below, to see how that would look?
 

kn0ppers

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I believe in science and engineering. The capacitors I use cause no measurable degradation of of the audio signal. Many so-called "audiophile" capacitors measure significantly worse than regular off-the-shelf components. What "audiophile" components seem to do really well is drain your wallet. If you want good performance, just shop at Digikey or Mouser.

Oh I wasn't even thinking about the "real audiophile" variety. I know you wouldn't select parts that measurably degrade performance, that's one of your main selling points after all. I wasn't questioning the decision, more trying to understand the thought process behind it. I mean you could have gone with a non-audio smd part, would have been cheaper in parts and easier automated assembly, but you didn't. Makes me think you actually see some value in these things, or the market does and the price premium isn't to bad so why not?

Anyway, I think the logo looks pretty good, the second version seems a little more "dynamic" to me, the first one seems more static. Might have something to do with the additional angled lines. I personally like the first one better tbh. But the star wars vibe really is strong with this one.
 

tomchr

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I mean you could have gone with a non-audio smd part, would have been cheaper in parts and easier assembly, but you didn't.
To be perfectly honest, I haven't measured the performance with a plain electrolytic cap in those spots. I went with the Nichicon Muse UES because I know they don't contribute anything to the signal and those spots are critical for signal integrity. I doubt other caps will allow me to get to -130 dB THD.

The single Muse cap by the headphone jack could be any bipolar cap. It's likely lower assembly cost to just use three Muse caps than to add another part to the parts cassette for the pick-n-place machine. The PCB will go though wave soldering for the connectors and switches anyway, so having a couple of caps along for the ride won't break the bank.

Thanks for the logo feedback. I prefer the more abstract version, actually. The first one. At least nobody has indicated that they fainted in disgust, so life is good. :)

Tom
 

kn0ppers

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You are probably right on the cost and I can see the reasoning behind the first part as well. Pretty much identical to why I decided to also order UESs. Also seen them in RMEs products, so can't be that wrong.

About the logo again: I can see why one would prefer the second version, I just believe the first one will look very good on an actual black enclosure with white print. If it's not too much work, you could make a 3D Model with the logos, that would probably give a better impression. But just my 2 cents.
 

tomchr

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The bright green caps do look good against the red PCB. I could see sticking with them for that reason alone. :)

Tom
 

ayane

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Kinda late, but is your name is misspelled in the logo? It is lacking an 'I' and reads "Christansen".
 

tomchr

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Yep. The second I is silent. Blind too, apparently. :) Yeah. I can't believe I didn't catch that. I usually go through my last name letter-by-letter in situations like this. The designer was rather embarrassed too.

Anyhow. Here's the final version.
TCA Logo - Blue - 290x123.png


Tom
 

tomchr

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I feel good about giving out these specs: 1.0 W (20 Ω), 1.0 W (32 Ω), 250 mW (300 Ω). SNR: 132 dB. Residual noise & hum: 1.25 uV RMS (20 Hz - 20 kHz, A-weighted). Channel separation: 95 dB (limited by the 1/4" phone connector). Multi-tone IMD residual (AP 32-tone, 100 mW, 300 Ω): <-140 dB (ref. 100 mW, 300 Ω). Output impedance: 35 mΩ (1 kHz).

The THD+N is below the measurement floor of the APx525 (and likely also below that of the APx555). I was able to build a 1 kHz notch filter and use a precision oscillator to tease out the THD. The first measurement below shows the harmonic spectrum with the amp providing 10 mW into 300 Ω. Note, however, that you need to add a correction factor to the harmonics to compensate for the attenuation of the notch filter at the harmonic frequencies. I added the EQ curve for you in the second plot (which is why the noise floor looks all wonky). The THD comes in at about -133 dBc (225 ppb or 0.0000225%). I feel good about saying <-130 dB for now.
The 60 Hz hum in the THD measurement is from the setup (the precision oscillator power supply to be specific), not the amp.

I'm still working on improving my THD measurement setup. My attempt of world domination the Baxandall/Cordell/Christiansen way didn't quite pan out. At least not at the first attempt. I have another precision oscillator coming. It's supposed to be able to get THD below -150 dBc, so there's room for improvement in the measurements below.

I will be exhibiting at RMAF in the "Headspace". I'll be collaborating with Ryan Redetzke of Redscape. If you're in Denver Sept. 6-8, feel free to swing by to chat and listen to the HPA-1 prototype.

I will open up for preorders before I leave for RMAF - so around Labour Day (Sept. 2nd). You'll be able to place your order here: www.tomchr.com. Currently the site is password protected. I'll remove the password once I'm closer to done with it. I hope to have the amps built and shipping by mid-November.
I expect the preorder price to land around $549 and the final price around $649-$699. I need to get some assembly quotes before I can promise anything regarding the pricing, but those are my estimates based on past experience with assembly cost. The preorder discount is ONLY available until the amps come back from assembly. Once I have amps in stock, the final price will kick in. I will NOT have sales aside from this preorder sale.

Tom
 

Attachments

  • TCA HPA-1_ Harmonic Spectrum (10 mW, 300 ohm, suppressed fundamental) - Annotated.png
    TCA HPA-1_ Harmonic Spectrum (10 mW, 300 ohm, suppressed fundamental) - Annotated.png
    43.3 KB · Views: 243
  • TCA HPA-1_ Harmonic Spectrum (10 mW, 300 ohm, suppressed fundamental, CORRECTED) - Annotated.png
    TCA HPA-1_ Harmonic Spectrum (10 mW, 300 ohm, suppressed fundamental, CORRECTED) - Annotated.png
    46.8 KB · Views: 241

tomchr

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I'm curious about that too. :) I'll wait until I have a better oscillator. I need to focus on getting ready for RMAF. There's no shortage of stuff to do.

I will post a full set of measurements when I can. I may hold off until I get the production amps in hand as I find the professionally assembled PCBs tend to perform considerably better than the hand-assembled ones. I would prefer to show valid data.

Tom
 

tomchr

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I know many of you have signed up for my Neurochrome Newsletter. Thank you! Now that TCA is up and running (more or less anyway), I have set up a dedicated mailing list for it. While tomchr.com is password protected (so for the next week or so), you can subscribe to the TCA Newsletter by visiting https://www.tomchr.com. Just type in your email address and click Subscribe. Some of you have done so already, which is awesome to see!

Once I remove the password protection (so Sept. 2 or earlier), there'll be a Newsletter Subscription form at the bottom of the home page.

You're obviously free to subscribe to both newsletters if you wish. But I will keep those brands separate and, thus, will send out newsletters that are tailored towards the respective audiences.

Oh... And in compliance with the Canadian anti-spam law, I also need to let you know that you're free to unsubscribe at any time. You can do so by clicking the unsubscribe link at the bottom of the newsletter email.

Tom
 

tomchr

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Moving beyond the vapourware stage. :) Pardon my feeble attempts at product photography. I'll follow up with better photography at a later date.

I think the prototype chassis turned out pretty nicely. I'll get some help with the graphic design for the final version.

The power-on indicator (above the power button) will move to the left of the power button and become a small dot (2 mm diameter) in the final version. I had planned to use an SMD LED and a flexible light pipe for the power-on indicator, but flexible light pipes turn out to not be very flexible and not intended for right angle bends. So the PCB had to grow to fit a leaded LED that'll be bent to reach the inside of the front panel.

The front panel Philips screws will be replaced with audiophile-approved Torx or socket head ones.
HPA-1_P1p1_ASSY.jpg
HPA-1_P1p1_wFocal.jpg


Tom
 

Hemi-Demon

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Looks good, but why no balanced output (XLR or 4.4mm)? Also is this RCA input only?
 
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