Neurochrome HP-1: Ultra-High End Headphone Amp

[jacques antoine]

I'm not sure where you get the $10 figure from.

Hi Tomchr,

The 10$ figure was not meant as a put down but very close to reality.
As I mentioned in the old build post, I obtained free chip samples from TI.
Most of the other components are chinese or bankruptcy surplus and were already lying in my DIY drawers.
My build is very far from being as pretty and fancy as yours but works better than other builds and commercial products I've tested.
I have never tried headamps in your price range which is way out of my league: small DIY player here.
I wish you a good success in business.

Jacques

 

[xrk971]

The schematic is in the LME49600 data sheet. National used the LME49720 for the DC servo which almost defeats the purpose. I've built that circuit. It works quite well, though it can be improved.

The OPA1611 provides better performance than the LME49720/LM4562 but does have a little phase wobble in the 1-10 MHz range that you have to deal with. Tradeoffs, tradeoffs.

The HP-1 contains $250 worth of parts, not including the PCB or the chassis, neither of which is cheap. I'm not sure where you get the $10 figure from. You can't even buy the chips for that. Besides, as I've noted earlier, I don't work for free. I'm in a low volume, niche market, so I have to have high margins to survive. Sorry. That's reality.

Tom

Tomchr,
At $250 parts and case is easily $80, custom 4 layer PCB's of this level of complexity are easily $100 in small quantities, your retail price is actually a steal as it includes assembly and test. Good luck on your business for this amp! I can't wait to hear it on the tour. I have some Class A heavy hitters to do AB test against. My latest is Salas DCG3.

 

[gentlevoice]

@Tom:

Hi Tom ... I've been reading about your modulus 86 & now the HP-1 and just noticed this a few posts higher up in the thread:

There's a loaner floating around in the US via the SBAF. I'll likely continue the loaner tour via Head-Fi as well. Toss me a PM or email if you're interested in joining.

I'd be interested in trying it out as well, if possible? I live in Denmark (might you have a connection here - your name is indeed very Danish ;-)) so somehow it needs be shipped back and forth without duties etc. Any chance it can be done?

Cheers,

Jesper

 

[tomchr]

I'm a native Dane and do occasionally make it back to visit friends and family. I have no plans for a trip to Denmark anytime soon, but if you can wait a few years I'm sure I can bring a loaner amp and ship it to you locally (or swing by to meet you if you're in the Copenhagen/Køge area).

Tom

 

[gentlevoice]

@tomchr:

I'm a native Dane and do occasionally make it back to visit friends and family. I have no plans for a trip to Denmark anytime soon, but if you can wait a few years I'm sure I can bring a loaner amp and ship it to you locally (or swing by to meet you if you're in the Copenhagen/Køge area).

Well, yes, your name did sound Danish ... Anyway, thanks for considering but waiting a couple of years to hear it is a bit too long for me to take into consideration right now - so unless some other opportunity shows up I'll have to pass on this. That said I'd like to add that you approach to engineering is quite inspiring and the results you achieve with global feedback also impressive. So ... good luck in your endeavors ;-)

Jesper

 

[Pars]

I'd agree with a previous poster questioning the choice of the Alps RK97 for the volume pot for this. The RK97 is a decent choice for an Altoids tin amp like a Cmoy. Something like this, which is supposed to be a high end amp; not so much.
If you need to retain the smaller form factor, then a TKD CP601 would be a much better choice at your price point. Or a CP2500 if you can deal with the size.


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[tomchr]

The TKD pot is ±3 dB channel matching - just as the ALPS RK097 used in the HP-1.

The channel matching is really only an issue below 40 dB attenuation. That's about 7:30 o'clock on the pot with 7 o'clock being the minimum setting. Or in other words: Not an issue for practical uses.

The ALPS RK097 is sonically transparent as far as I can measure. It's a CERMET pot, so it should be very durable. If there is an issue with the volume pot, I think it's a marketing issue rather than a technical issue. I don't do bling pots...

Tom

 

[tomchr]

Well, yes, your name did sound Danish ... Anyway, thanks for considering but waiting a couple of years to hear it is a bit too long for me to take into consideration right now - so unless some other opportunity shows up I'll have to pass on this.

Fair enough. You can always subscribe to my newsletter (here). I'll let people know when there's a Europe trip coming up so you can save a buck or two on the import fees.

That said I'd like to add that you approach to engineering is quite inspiring and the results you achieve with global feedback also impressive. So ... good luck in your endeavors ;-)

Thank you.

Tom

 

[agdr]

The TKD pot is ±3 dB channel matching - just as the ALPS RK097 used in the HP-1.

I hadn't heard of those TKD pots before. I pulled up the datasheet out of curiosity. Figured I must be missing something - 20% and 3dB, exactly like the RK97. For that kind of money I was expecting to see 5% (the Alps and Bourns 9mm come in 10% too) and 1dB tracking. Maybe the the larger THD pot has some of those, I didn't look at that datasheet. But the 600 series appears to be just $90 of additional profit, at least from the datasheet specifications.

 

[cwtim01]

The TKD pot is ±3 dB channel matching - just as the ALPS RK097 used in the HP-1.

There is a more detailed version of the datasheet for the TKD 2CP-601 (attached), which states:

Matching Accuracy (At Log Taper)
0~10dB ±0.6dB
20dB ±1.0dB
42dB ±2.0dB

These quality pots tend to measure quite better than the datasheet also. Another point worth noting is that the TKD has a life of 100K cycles, versus the 15K cycles of the RK097.

RK097 is probably value for money, but it's not very fitting to find it in an "Ultra-High End" headphone amp.

 

[tomchr]

Nice pot! Unfortunately, it does not seem to be available at Mouser or Digikey, which means I'll be stuck importing potentiometers.

I'm not able to measure any impact of the RK097, so I maintain that this is an issue of marketing/perception rather than a technical issue. I measure better than ±0.1 dB tracking on the RK097 (I've measured several of them).

That said, I can certainly look into what it would take to get the TKD pots in and use those instead. It is better spec'ed and if it makes for better marketing copy and helps me sell more amps, I'm all for it. Thanks for pointing me to this.

Tom

 

[agdr]

Matching Accuracy (At Log Taper)
0~10dB ±0.6dB
20dB ±1.0dB
42dB ±2.0dB

These quality pots tend to measure quite better than the datasheet also. Another point worth noting is that the TKD has a life of 100K cycles, versus the 15K cycles of the RK097.

Interesting! Thanks for that.

So it looks like the matching accuracy is a lot better on the low end. I don't use Alps in my projects anymore, way to many out-of-the-box failures on their 9mm, I switched to Bourns a long time ago. I'm going to see if I can get similar low-rotation matching figures from Bourns. Just curious. That 3dB on the 9mm pots is probably also a maximum at large rotation.

And good find on the maximum rotations! No ambiguity there, that is nearly 7x the rotational life.

Here are the TKD 601 10K stereo at Parts Connexion in Canada, $39:

More Information Page

in my quick look earlier I must have been looking at the 2500 series ($99), which is why I thought they were $90 more.

 

[tomchr]

$39!! Holy moly! I'll check around and see if I can find better deals elsewhere.

I do understand that you often get what you pay for, but $39 sounds a bit high. An ALPS RK271 is less than $20 and, while not as good as the TKD, basically the gold standard pot.

Tom

 

[Pars]

Not really... The gold standard pot would probably be an Alps RK50 or a Penny & Giles.
I like the TKD CP2500 much better than an Alps RK27, and to me they are worth the premium. Subjective.
Since you are in Canada (I believe?) you should be able to buy directly from TKD. In the US they make you go thru their US distributor so pricing isn't as good.


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[tomchr]

Even the P&G pots don't track all that well from what I understand.

I think the TDK has more going for it.

Tom

 

[ammel68]

I haven't seen or heard of a Penny & Giles pot in years. I remember seeing them in select Aragon preamps probably 20 or more years ago.

Are they still being made?

 

[tomchr]

Apparently, P&G were acquired by Curtiss-Wright in 2002. You can still get the faders but the rotary pots appear to have been discontinued. Now, if you wanted to control the volume by joystick, CW appear to be able to get you hooked up.

Tom

 

[ammel68]

Thanks Tom. I figured something must have happened to them since I don't hear them mentioned much anymore.

Think I'll pass on the joystick idea.

Instead, I would like to get about dozen of these:
One pair PHILCO GA-51812-L1 31 step volume Attenuator (modified A100K log) | eBay

Philco...the ULTIMATE volume control!

 

[chinook9]

I am in the process of determining if I have the ability to build an HP-1. I have built a Buffalo IIISE and a couple of DIYINHK dacs and PSs as well as a couple of other kits. All worked first time, so I'm not real concerned about my BASIC soldering abilities. The concern lies in my ability to solder SMDs of the size in the HP-1.

To this end I purchased an SMD practice kit and have done OK using a soldering station. I also have a cheapie hot air gun (858D+) and I just used it with soldering paste to solder a few parts.

Use of the solder paste and hot air gun seemed to be quite easy and fast and I am wondering if anyone on this forum used this method or if there are factors that make this a poor choice.

Also, I am not a EE, so if the end result doesn't work, I can check for bad joints or misplaced parts, but troubleshooting beyond that might be a challenge. I'm willing to take this chance if I feel I can make good solder joints.

 

[tomchr]

I'd try to solder with thin (I use 0.5 mm diameter) solder and 0805 components on your practice boards. If you can do those reliably, you should not have issues assembling the HP-1.

In my experience solder paste always ends up making a mess if you don't use a stencil. If it works for you, great. No harm in using it. I don't have an air gun that's suitable for soldering, so I stick with thin solder and a fine tip on my METCAL.

If the end result doesn't work, we can likely debug it via email if you have the basic tools (definitely a DMM. An o'scope is nice.) If that fails, there's always the option of shipping the board to me for me to fix. I won't leave you hanging.

Tom