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

[tomchr]

...and there went your RFI/EMI shielding. Sorry. Increasing the chassis cost to end up with a lower quality product is not my idea of a good time. How much extra would you be willing to pay for a lower grade product with a window?

Tom

 

[Hugo9000]

My site is up and open for pre-orders: www.tomchr.com I suppose I should edit my signature line at some point...

Tom

Congratulations and best wishes! I really like the clean site. Your enthusiasm for your products and your work ethic come through beautifully in your statements throughout the site. I love that you included your academic credentials, mentioning your history of interest and experience and expertise, all without conveying any arrogance. Very nice balance of confidence and qualifications, while keeping it light. Including a link to your resume was a nice touch for those that might want to see a little more depth, without anyone being able to accuse you of dwelling too much on that side of it. Bravo!

I have a couple of very minor points, though, at the risk of coming off as a nitpicker (or worse haha). There is a pic that cycles with your equipment photos, that I assume is just a temporary filler. Since it has a handbag, a shoe, and some other goods, I assume it's supposed to suggest luxury products? It looks like a placeholder, I'd get rid of it before the google bots add it to images linked to your site haha!

The other has to do with the footer menu. That text, "Footer Menu" is still there, but it might appear to have been placeholder text in a website builder to some visitors/customers. Anyway, my apologies if you put it there intentionally.

Oh, one more thing: I realize your work speaks for itself, but you might consider linking to the measurement and review threads here that discuss your designs. Perhaps add a FAQ item about outside testing and verification of your measurements or something similar? I don't want to sound presumptuous (probably way too late, sorry), you probably did consider it and chose not to link for some reason (maybe it would trigger people at certain forums who might otherwise want to purchase your beautifully-engineered products--I would hope not, but one never knows).

Again, congratulations on the next step in your new equipment branding and product/website launch, and best wishes for great success!

 

[tomchr]

Congratulations and best wishes! I really like the clean site. Your enthusiasm for your products and your work ethic come through beautifully in your statements throughout the site. I love that you included your academic credentials, mentioning your history of interest and experience and expertise, all without conveying any arrogance. Very nice balance of confidence and qualifications, while keeping it light. Including a link to your resume was a nice touch for those that might want to see a little more depth, without anyone being able to accuse you of dwelling too much on that side of it. Bravo!

Thank you. I really appreciate your thorough review and positive feedback.

I have a couple of very minor points, though, at the risk of coming off as a nitpicker (or worse haha).

There is a pic that cycles with your equipment photos, that I assume is just a temporary filler.

The other has to do with the footer menu. That text, "Footer Menu" is still there, but it might appear to have been placeholder text in a website builder to some visitors/customers.

Dang! Good catches there Eagle-Eye! Thank you!

The additional slide in the slide show was probably from a finger slip at some point. I have no plans for selling handbags or shoes anytime soon, if at all.

Good point with the Footer Menu heading. I changed it to "Further Information" as I wasn't able to disable it outright. It's good for now, I think. Please, let me know how you like "Further Information". Does it seem out of place or redundant?

Oh, one more thing: I realize your work speaks for itself, but you might consider linking to the measurement and review threads here that discuss your designs. Perhaps add a FAQ item about outside testing and verification of your measurements or something similar?

I do plan to write something about how measurements and the perceived experience are linked. Sort of what I do along the individual plots on my Neurochrome site, but fleshed out more. Also, once I get an amp to Amir, I'll be linking to his results. Same for reviews when they happen. I also plan to open up for buyer reviews once enough amps have gotten into people's hands.

I appreciate your insights and ideas, actually. Thanks. I've had quite a few of those ideas myself.

Tom

 

[Hugo9000]

Thank you. I really appreciate your thorough review and positive feedback.


Dang! Good catches there Eagle-Eye! Thank you!

The additional slide in the slide show was probably from a finger slip at some point. I have no plans for selling handbags or shoes anytime soon, if at all.

Good point with the Footer Menu heading. I changed it to "Further Information" as I wasn't able to disable it outright. It's good for now, I think. Please, let me know how you like "Further Information". Does it seem out of place or redundant?


I do plan to write something about how measurements and the perceived experience are linked. Sort of what I do along the individual plots on my Neurochrome site, but fleshed out more. Also, once I get an amp to Amir, I'll be linking to his results. Same for reviews when they happen. I also plan to open up for buyer reviews once enough amps have gotten into people's hands.

I appreciate your insights and ideas, actually. Thanks. I've had quite a few of those ideas myself.

Tom

I think it looks great, and I'm glad you took my comments in the spirit that I intended them! I don't always know how I come across, other than being aware that I'm a colossal windbag haha!

My favorite quote from Anne of Green Gables: "I know I chatter on far too much... but if you only knew how many things I want to say and don't, you'd give me some credit!"

 

[phpp]

@tomchr How well does the HPA-1 handle sensitive headphones like the Oppo PM-2? I listen at fairly low volume levels and find that most amps have way too much power for that. I usually have to set the volume knob at the very low end which often leads to channel imbalance.

 

[tomchr]

You should be fine. The HPA-1 has unity gain at its lowest setting, so you'll get ~100 dB SPL peaks at about 12 o'clock on the volume control with a 2 V input. 2 V is what I'd expect from a DAC or CD player. Many handheld devices deliver less.

Tom

 

[Azeia]

I'm toying with the idea of a DIY headphone amp. It'll be lower spec than the HPA-1 and it will *NOT* be available as an assembled product. I don't want to compete with myself.

Thanks for the link to newsletter, I've subbed now, although I guess there's no way for me to receive past issues so I guess I missed this one. When you say "lower spec" do you mean in THD+N like the HP-1, or also in power? Like is there any possibility of the HP-1 (or a variation of it) coming back as DIY-only? (perhaps even with no chassis as just a board and parts list).

The downside of this is that we'll likely have to wait until Christmas to get Amir's results...

How long will the preorder price be available? I suppose there's no chance we'll be able to get Amir's measurements in time to take advantage of the introductory price?

 

[YoloSwag]

@tomchr Have you try BUF634A yet? TI seems to updated the classic LME49600/BUF634. The 2nd & 3rd Order Harmonic distortion in HP-1 amirm tested was really low, it looks even better than Benchmark HPA4. Is it benefited from the DC servo?

 

[bgsprtm]

i'm sorry for the noob question, so what is the benefit of xlr input? does it produce more clearer sound?

 

[ayane]

i'm sorry for the noob question, so what is the benefit of xlr input? does it produce more clearer sound?

Common-mode noise rejection. It's a more reliable interconnect and can improve the system SNR.

 

[Julf]

i'm sorry for the noob question, so what is the benefit of xlr input? does it produce more clearer sound?

Common mode noise rejection, only an issue with very long cables or very electrically noisy environments (factory, stadium), as well as helping to avoid ground loop issues.

 

[SIY]

i'm sorry for the noob question, so what is the benefit of xlr input? does it produce more clearer sound?

To clarify, it’s not that it’s XLR, it’s the use of balanced lines that achieves noise rejection. XLR is just one of the common connectors used for balanced lines.

 

[Julf]

To clarify, it’s not that it’s XLR, it’s the use of balanced lines that achieves noise rejection. XLR is just one of the common connectors used for balanced lines.

Indeed. Good to point out that distinction - and the ground loop avoidance comes from the differential input circuitry.

 

[tomchr]

Thanks for the link to newsletter, I've subbed now, although I guess there's no way for me to receive past issues so I guess I missed this one.

My first TCA Newsletter basically announced the preorder sale on the HPA-1. If you've been following here, you haven't missed a whole lot.

When you say "lower spec" do you mean in THD+N like the HP-1, or also in power? Like is there any possibility of the HP-1 (or a variation of it) coming back as DIY-only? (perhaps even with no chassis as just a board and parts list).

The DIY headphone amp I'm mulling over would run off of a laptop charger, so you'd be limited to +20-24 V. This means you'll get an output capacitor, lower power, and higher distortion.

How long will the preorder price be available? I suppose there's no chance we'll be able to get Amir's measurements in time to take advantage of the introductory price?

The preorder pricing ($549 rather than the target price of $699) will apply for the first 40 HPA-1s or until the HPA-1s arrive from the assembly place (whichever comes first). Right now, there are 31 left at the preorder pricing.

You can find my measurements of the HPA-1 on the HPA-1 product page. My measurements are done with an Audio Precision APx525, whereas Amir's are done with the APx555. His measurements will be better than mine as my APx525 has a higher noise floor and higher residual THD than his does.

@tomchr Have you try BUF634A yet? TI seems to updated the classic LME49600/BUF634. The 2nd & 3rd Order Harmonic distortion in HP-1 amirm tested was really low, it looks even better than Benchmark HPA4. Is it benefited from the DC servo?

I haven't messed with the BUF634A. Last I looked at its data sheet, it didn't seem to offer anything I couldn't get in the LME49600, so I didn't bother with it.

i'm sorry for the noob question, so what is the benefit of xlr input? does it produce more clearer sound?

I agree with what's been said above. I generally find the XLR sounds better. I suspect the improvement is caused by getting the ground loop out of the signal path. Also, many high-end DACs now come with differential/balanced out and buyers would like to use them.

Tom

 

[tomchr]

The HPA-1 is coming together. The trial run of the final chassis was successful as you can see in the images. I'm basically waiting on vendors to deliver parts so I can send it all out for assembly. I'm having Alps make a custom RK271 for me for the volume control, so that takes a while. I should be able to ship by early/mid December, though. I really want people to have these by Christmas.

Tom

 

[LuckyLuke575]

The HPA-1 is coming together. The trial run of the final chassis was successful as you can see in the images. I'm basically waiting on vendors to deliver parts so I can send it all out for assembly. I'm having Alps make a custom RK271 for me for the volume control, so that takes a while. I should be able to ship by early/mid December, though. I really want people to have these by Christmas.

Tom
View attachment 38052View attachment 38053View attachment 38054

This is a handsome amp for sure. However it looks like the blanced output is gone??? Is this the same amp just SE? What's the price?

 

[restorer-john]

Wow! It's beautiful on the inside and the outside. The sub panel for the jack and the pot are perfect. High quality latching push switches. Wow.

(what about the earth pin on the IEC? in the photo? Just not fitted for the pic?)

Awesome work.

 

[restorer-john]

Tom, it is unusual to have the Right RCA input above the Left. I don't think I've ever seen that done before.

Your other picture has the left on top, as is traditional.

I guess it doesn't really matter in the long run, March Audio has his lefts and rights on the opposite sides of his rear amp panels to conventional gear.

 

[tomchr]

This is a handsome amp for sure. However it looks like the blanced output is gone??? Is this the same amp just SE? What's the price?

The HPA-1 is actually a complete redesign. There are many reasons for this. Here are some of them:

• The Neurochrome HP-1 was truly a cost-is-no-object design. It was an engineer's amp. Sadly, this meant that while it provided awesome performance, it was ill suited for mass production. And, as many pointed out, the chassis design of the Neurochrome HP-1 left quite a bit to be desired. That said, it was an amazing learning experience for me and I have carried those learnings into my Tom Christiansen Audio HPA-1.
• Neurochrome provides products for the DIY market. DIY is often perceived as cheap. It turns out it's hard to charge a premium for a well-designed product if you're perceived as cheap. So going forward Tom Christiansen Audio (TCA) will provide my retail products and Neurochrome will provide DIY products. I will not deliver fully assembled in-box Neurochrome products. Only TCA products will be retail products.
• The TCA HPA-1 was designed from the ground up as a retail version of the HP-1. The amplifier architecture is similar (both have a composite amplifier output stage), but that aside, the HPA-1 does not share any of the HP-1's circuit design.
• My goal with the TCA HPA-1 was to provide HP-1 performance at a much lower price point. I had to trade off a little on the output power, reduce the number of gain settings to two, and drop the 4-pin output to meet this goal. To me those were fair tradeoffs.
• The TCA HPA-1 provides a unity gain setting (requested by many). The lowest gain on the Neurochrome HP-1 was +6 dB.
• The TCA HPA-1 looks to be providing even lower THD than the Neurochrome HP-1. I am still working on improving my measurement capabilities so I can actually measure it.

The TCA HPA-1 is currently on early-bird special. The first 40 preorders will be heavily discounted. After the first 40 orders (or when the HPA-1 arrives in stock, whichever occurs first) the price will jump to the final price and stay there. I'm planning to take a page from Schiit's playbook and not have sales aside from the early-bird special. I've never seen a sale that resulted in an increase in the number of orders, which makes them rather pointless. Also, now that most of the numbers are in, it looks like I'll have to increase the final price to $899. Western manufacturing is expensive, but the quality is there too!

Aside from a few forum posts here, the occasional Facebook post, and my attendance at RMAF, I've done no advertising for this amp. Yet, I'm nearly halfway through the first 40 preorders. If you'd like to take advantage of this, I suggest placing your order soon. Do beware that I don't expect to have the first batch in stock until early/mid December, however. The discount is my way of thanking you for your patience and support.

Wow! It's beautiful on the inside and the outside. The sub panel for the jack and the pot are perfect. High quality latching push switches. Wow.

Thank you. Yeah. I figured you'd like the sub panel.

(what about the earth pin on the IEC? in the photo? Just not fitted for the pic?)

The IEC is grounded through the PCB to a solid stainless steel standoff pressed into the bottom panel of the enclosure.

Awesome work.

Thank you.

Tom

 

[tomchr]

Tom, it is unusual to have the Right RCA input above the Left. I don't think I've ever seen that done before.

All the gear I grew up with had right above left, so having right at the bottom felt awkward to me. Before I selected that connector (and, thus, right above left as "red is right"), I did perform a brief scan of various bits of commercially available gear. I found plenty of examples of "right above left", so I moved on. The only "standard" manufacturers seem to agree on is that the right connector is to the right when you look at the chassis from the front. So that's why the XLR connectors are placed the way they are.

But as you say, it doesn't really matter. The connectors are clearly marked, so there shouldn't be much ambiguity.

One thing that did drive the choice of this connector was that I wanted it gold plated. The gold plated version with the right (red) connector on the bottom was special order. The version I use is readily available. I'm sure you've seen enough oxidized nickel plated connectors in your lifetime.

Tom