[Armaegis]

Hey guys, I just posted up my review (hope I didn't goof up the formatting anywhere):
http://www.head-fi.org/t/830987/review-neurochrome-hp-1-making-sweet-love-to-your-hd650-or-what-the-o2-wishes-it-could-be

 

[bluemonkeyflyer]

Hey guys, I just posted up my review (hope I didn't goof up the formatting anywhere):
http://www.head-fi.org/t/830987/review-neurochrome-hp-1-making-sweet-love-to-your-hd650-or-what-the-o2-wishes-it-could-be

I ordered the Neurochrome PCB, yesterday. After reading your excellent review, I'm glad I did. Well done and very detailed review! Many thanks.

~ BMF

 

[bluemonkeyflyer]

Neurochrome HP-1 arrived today. I'm looking forward to taking it for a test drive.
 

 

[Armaegis]

@bluemonkeyflyer Any update on impressions so far?
 
 
I thought I would share this link as well, to show how thorough Tom can be when it comes to measurements.
http://www.neurochrome.com/sjostrom-qrv08-headphone-amp/
 
Rumour has it Tom also has an O2 in his possession and will be running a full suite of measurements in the near future.

 

[tomchr]

Rumour of an O2 in the stack of gear to be measured is hereby confirmed. I'll add it to the "Measure Your Gear" section of my website once the data are available. Late this month or early next month seems like a realistic target for publication.
 
Tom

 

[grizzlybeast]

If the O2 measures well but sounds like garbage (to my ears) what would that mean?

 

[tomchr]

I'm sure there's a long thread on measurements vs perceived experience somewhere on Head-Fi. They tend to devolve into a shouting match between objectivists and subjectivists and can be incredibly time consuming to participate in. While I do enjoy a good discussion, I simply do not have time to participate in those shouting matches and have no interest in turning this thread into one.
 
There's an overwhelming body of research evidence that supports that good measurements (plural) correlate strongly with a positive listening experience, on average. You can consult the work of Sean Olive and Floyd E. Toole for examples.
As with any psychological or perception research, these data apply to populations on average. Populations (in Olive & Toole's case) consisting of trained listeners, audiophiles, and untrained listeners. They do not include you specifically. If your personal preferences are significantly different from those of the average trained listener, untrained listener, or audiophile, you will have to figure out which measured parameters do correlate well with a positive experience for you and find an amp that does that.
 
As an amplifier designer, I can choose to design for good measurements or I can choose to design an amp that adds a little "something-something" (2nd and 3rd order harmonics) to the sound. I've done both and made them publicly available. Whether those designs deliver a perceived sound quality that you prefer, I don't know as I don't know what your preferences are. However, I do make it possible for you to be an informed consumer as I do present measurements of the amplifiers so you can make an informed purchasing decision.
 
Hope this helps.
 
Tom

 

[bluemonkeyflyer]

@Armaegis,
 
I don't think I can add anything substantive to your excellent review and description of HP-1. I liked HP-1 a lot during my brief audition. It's very clean with balanced FR, good punch, smooth mids, good treble extension/air/details, and wide soundstage.
 
I compared HP-1 to several amps including my QRV-08. I like both very much. Despite measurement differences posted by Tom, I could not hear any difference in sound quality. I used SPL matching, an amplifier switching box for quick changes, and a friend did the switching...then we switched places and he couldn't reliably distinguish them, either. HP-1 will play louder on higher gain but Tom recommends lower gain for better performance.
 
I ordered the HP-1 PCB and chassis from Tom and they are inbound. I ordered the BOM from mouser and they upgraded my shipping from UPS ground to Next Day Air. I'm looking forward to the build and having a lot more time to compare to my other amps.
 
~ BMF

 

[Armaegis]

  As an amplifier designer, I can choose to design for good measurements or I can choose to design an amp that adds a little "something-something" (2nd and 3rd order harmonics) to the sound. I've done both and made them publicly available.

 
Designing for a little "something-something", is this by leaving distortion products in or are they literally "added in" ?
 

  I ordered the HP-1 PCB and chassis from Tom and they are inbound. I ordered the BOM from mouser and they upgraded my shipping from UPS ground to Next Day Air. I'm looking forward to the build and having a lot more time to compare to my other amps.
 

 
I'm curious to hear about your build experience when you do it. Reportedly, the QRV08 is one of the harder DIY headamp projects out there, so I'd like to hear how the HP-1 assembly stacks up against it.

 

[tomchr]

I'm not aware of any amplifier that is capable of removing anything from the source material. Thus, if the source contains distortion, the amplifier will reproduce it. I suppose a severely bandwidth limited amplifier could remove frequency content from the source material, but if we're talking amplifiers used for audio reproduction in a hifi sense, they should not be bandwidth limited. This is easy to confirm by measurement.
 
A perfectly linear amplifier would reproduce Vout = Vin * A. However, such an amplifier only exists in theory. Any real amplifier will not be perfectly linear. It'll usually operate on a "linear" portion of an exponential (BJT) or square law (FET or vacuum tubes). This means any real amplifier will add distortion. So if a perfect sine wave with a frequency, f, is presented to the amp input, the amp will produce f, 2f, 3f, ... nf. The key for a clean design is to keep all the harmonics (2f, 3f,... nf) as low in amplitude as possible, thus approaching the theoretical amp. The HP-1 comes very, very close to that theoretical amp.
 
The DG300B, by contrast, is not all that linear (by modern standards anyway). At 1 W into 8 Ω, its THD is about 0.2 % and the harmonics are clearly visible in the frequency spectrum measurements. In case of the DG300B, if you present a clean sine wave on the input, you will definitely get 2f, 3f, and some 4f components (2nd, 3rd, and 4th order distortion products) on the output. The 2f component will be about 0.1-0.15% of the amplitude of the input sine wave and the RMS sum of the 2f, 3f, 4f (and noise) components will add up to 0.2 % of the fundamental power. This is from the transfer function of the 300B and driver tubes as well as the output transformer. Physics! It's a thing.  
 
Tom

 

[Armaegis]

  The DG300B, by contrast, is not all that linear (by modern standards anyway).

 
Thanks Tom. My question was worded poorly, but the answer I was looking for was given above. Can the distortion products produced by an amp be specifically tuned if someone desired to do so?

 

[bluemonkeyflyer]

 
 
I'm curious to hear about your build experience when you do it. Reportedly, the QRV08 is one of the harder DIY headamp projects out there, so I'd like to hear how the HP-1 assembly stacks up against it.

The QRV-08 is very challenging. It has 300 SMD components and somewhere around 900 solder joints. It's sometimes difficult to determine the part labels printed on the PCB requiring a careful study of the schematic and circuit traces layout. The SMDs are mostly 0805 caps/resistors (2.0 x 1.25mm) and SOT23 transistors (2.8 x 1.5mm). IIRC, the ICs have a pitch of ~ 0.75 and there are 14 of those. Having said all that, with experience/practice, a few simple techniques, and the proper tools it's really not difficult. In fact, I prefer hand soldering SMD boards over through-the-hole boards any day.
 
Comparing HP-1 and QRV-08 PCBs, I don't think there is any doubt that HP-1 will be a much easier build due to:
fewer parts
less dense layout
better setup and build instructions

 

[jh4db536]

The most difficult parts on the hp1 are the sot23, possibly the tiny diodes, and the lme opamps, but it wasn't that hard overall because it's not that dense and the board labels are printed very nicely. Getting parts out of the packaging takes long.

I have no preference between SMD or through hole anymore...

 

[tomchr]

  Thanks Tom. My question was worded poorly, but the answer I was looking for was given above. Can the distortion products produced by an amp be specifically tuned if someone desired to do so?

 
You cannot change the fact that harmonics show up at integer multiples of the fundamental frequency. So input 1 kHz pure sine wave, get 1,2,3,4...n kHz out (1 kHz fundamental + harmonics). That's how harmonic distortion works.
 
What you can change, to an extent, is the composition of those harmonics. For example the THD in the DG300B is predominantly 2nd and 3rd harmonic and their amplitudes are some 50-60 dB down from the fundamental. They're not objectionable, but they do add a little "something-something". That may be why many find that amp to be engaging and provide an "out of the head" presentation.
Then contrast that with the HP-1 where the THD is 135 dB down (inaudible). If you're into listening to the source material, amplified, you'll like it. But if you're used to a tube amp, you'll find that "something-something" missing. This is due to the circuit architecture of the HP-1 (and other low THD amps).
Whether you want your amp to present the source material, amplified, or if you'd rather that the amp presents the source material amplified, plus "something-something", depends on your personal preferences.
 
The short answer to your question is: To "dial in" the THD profile of a circuit you need to change the architecture. Alternatively, you can add (predominantly) 2nd order harmonic distortion by adding a clipper. In a discrete circuit, you may also be able to get the THD profile you want by varying the bias points. I suggest googling/binging "tube emulator circuits" if you're interested in how to add THD to a circuit.
 

The most difficult parts on the hp1 are the sot23, possibly the tiny diodes, and the lme opamps, but it wasn't that hard overall because it's not that dense and the board labels are printed very nicely. Getting parts out of the packaging takes long.

I have no preference between SMD or through hole anymore...

 
I generally find SMD easier to deal with as there are fewer pins to bend and clip. That said, I can populate a leaded board blindfolded. That doesn't work so much for an SMD build. The little SOD-323 diodes are annoying! They're the smallest parts on the HP-1. SOT-23 is much easier to deal with but in the locations where the SOD-323 are used, the SOT-23 versions of those diodes would blow up the layout.
 
The main reason the HP-1 is SMD is to be able to do automated assembly. In addition, I can't get the exciting parts in leaded packages, so SMD it is.
 
Tom

 

[JeremiahS]

I need to spend more time with this amp to determine. I will likely send it out on a loaner tour so more people get to hear it.

Beta22 is probably not very transparent as it imparts its MOSFET sound signature on everything. My main gripe with the beta22 is that I wish it was more crisp/definite and less polite/more aggressive. The b22 is one of the few SS amps that don't have an offensive treble and complete lack of glare, which is very important attribute for me which is why it remains my main SS amp despite its other shortcomings. It also has a lot of power on tap, so it should be able to power just about anything.

Jot from memory seemed have some transparent tendencies. I was able to play with different sources CDP, external DACS, turn table and internal dac with the jot.

 
Hi jh4db536,
 
Thank you for the brief comparison with Beta 22. I think it is a bit of shame that the Beta 22 does not get much discussions anymore because it has a very nice sound signature, that tube wetness especially in the midrange combined with solid-state precision and slam. Also it is not bright and sterile like most recent flagship amps made like the GS-X MK2 or Ragnarok, like you noted. 
 
I think you can make the Beta 22 more aggressive by increasing its bias current, if I remember correctly my builder told me that the values that Ti Kan set is very conservative and you can easily increase it if you have sufficient cooling for the MOSFET. 
 
HP-1 is definitely interesting me as I thought I need something more compact that I can take in the briefcase for working trips and my builder asked me to check it out and he generally has a good eye for good designs. I'm looking forward to hear more of your impressions. 
 
Thanks,
Jeremiah