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Tom Christiansen Audio HPA-1 Headphone Amp Review

kn0ppers

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It also gives me a target for the large-and-in-charge amp with 4-pin XLR output that I've been mumbling about. Thanks. :)
Remember, you need 120V discrete OpAmps to compete with them, because OpAmps running on low supply rails are bad mhhkayy. And you also need to give the THD+N for your headphone output into a 100kOhm load. If they are trying to sell to enthusiasts and professionals alike, why do they need to do this stuff? I guess because the so called "audio professionals" that are so regularly attested with substantial knowledge of analogue electronics in reality are pretty vulnerable to this kind of "facts". Or maybe they market to them via the extensive set of features that consumers don't actually need and the 120V OpAmp stuff is mainly targeted at the latter. However, not a fan, RME does that better. By that I mean finding the line between ornate language regularly used in audio marketing and sticking to the actual facts.

Needless to say that I think you can and probably will do better than SPL, both in most performance figures of interest as well as marketing. Maybe I'll be tempted to upgrade from the HP-1. Will there also be a questionnaire like for the HPA-1 or are you working with the data from the last one as well as customer requests you collected at the Expos you frequented? Will you target mainly consumers or also professionals?
 
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@kn0ppers it is really +/-60V rail to rail op-amp that yes they using creative marketing on, there are time and place to have more voltage swing for certain solutions. Remember the SPL Phontior x is not just for Headphones but also pre-amp for powered Speaker and amplifiers. This really more to deal with cascading gain which you can see in the professional market which also deals with different line-level inputs. Also, It has been interesting to see how different DAC really behaves on outputs. One thing is helpfull are the VU meter to watch what goes on at the input.

I have one I would not have paid full price for it, instead, I found a B-Stock unit 50% off with onboard DAC-192. It is not bad AMP for driving my Focal Nearfield monitors and tougher headphone like LCD-4 and Beyerdynamic DT880 600 Ohm speakers. I use it in conjunction with Universal Audio Apollo x8 so I have more headphones outs something test against other UA onboard headphone amp.

Yes, the updated RME DAC is a great solution for DAC and now an even headphone amp and even pre-amp for nearfield monitors. It has some very nice features like the onboard eq.

Honestly, these are just tools we all use to do a job, everyone is going have a different opinion about what is good or bad. At the Professional recording level, there is a lot more gear in the chain. It not just for laid back listening.

I love my HPA-1, this is what this section of the forum is about, from a performance perspective and its size it is one of my favorite amps. The amp has plenty of power for Single-ended use for most headphones. It finally made AEON FLOW Open Headphones enjoyable and not muddy, which is low impedance and low sensitivity headphones which creates a current pig. It is also great with the Ananda, RAD-0, HD-H650, and ELEX.

When tom ready to take on larger XLR amp I know it will be great. He is an analog designer and magician at it. Personally I love to see what he would do with DAC like AKM4499 since it analog section ( power and pre-amp) I care about. Topping D90 has a nice design, but it would be interesting to see what Tom would change.
 
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kn0ppers

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First off, I respect Tom and his work a lot and he is a great analog engineer, but not a magician. As someone with an engineering degree I don't think there is any need for this terminology in this context. There is engineers, good engineers, great engineers, but no magicians in my book. Magic usually can't be explained, while engineering is the exact opposite of that. We mathematically model (almost) everything we can, as precise as feasible/practical and then try to optimise what we can, given the technical and financial constraints. If being good at that makes someone a magician in your eyes, so be it.

Secondly, I think I am aware of most advantages and disadvantages of higher supply rails. I didn't check the Phonitor thing in detail, but I remember it said Headphone/PreAmp and I didn't find a serious reason why one would need such high rails (which doesn't mean there isn't one - I might have overlooked something). I am not a studio guy, but if I remember correctly the peak line level in professional environments is +24dBu, or around 12Vrms (*sqrt(2)*2= 34V p-p). There are off the shelf OpAmps that can handle this. But sure, if you want to drive 1W into 600Ohm Headphone loads, you won't get away with that. Then again who needs that, even in a studio environment? I don't see how cascading gain or "a lot more gear in the chain" creates a need for such high supply rails. Or what this has to do with laid-back-listening?! There are certainly good reasons for higher supply rails, but I struggle to identify them in a Headphone Amp. Be it for consumer or professional environments.

Last but not least: Maybe Tom will do a DAC in the future (although I don't necessarily expect it), but why should he use the AK4490? There is a newer version of that called the AK4493 if I am not mistaken. If you mean their high-end parts its AK4497EQ and the new one is the AK4499EQ. I would also be interested to see what he would do with it, but I suspect it wouldn't be much different from what other designers do. No point in reinventing the wheel. I personally would stick pretty close to what AKM themselves do for their demonstration circuits. They use lots of OPA1612s for the I/V and differential stages, I think at ESS they do the same thing on their evaluation boards, so does TI in application circuits for the OPA1612.
 
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@kn0ppers it is an expression, It means he is a very good analog engineer. I am an engineer I get it, I build super-computers and high-performance GPU's for my day job.

You need to talk to SPL why they want that much headroom in their Opamp. As I said it not just headphone amp

I meant the AKM4499 it was a typo.
 

tomchr

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Remember, you need 120V discrete OpAmps to compete with them, because OpAmps running on low supply rails are bad mhhkayy.
Uh. Yeah... About that. "Discrete opamp". That's another trigger word for me. :) I think there was a time and a place for them before, say, 2005 when the LME49720/LM4562 was released. Of the few of them that have an actual data sheet, I have found several that are only unity gain stable (i.e. are not guaranteed stable at higher gains). I'd be very careful before plopping those into any circuit with gain or EQ function (RIAA preamps, for example). I have found one that's as good as the LME49720, but it's 20 times as expensive (QTY 1 pricing) and likely much more expensive at the production volumes I tend to run. I remain unimpressed.

Maybe I'll be tempted to upgrade from the HP-1. Will there also be a questionnaire like for the HPA-1 or are you working with the data from the last one as well as customer requests you collected at the Expos you frequented? Will you target mainly consumers or also professionals?
The market survey I launched last year was very useful in the design of the HPA-1. There were definitely a couple of "we want" features that I hadn't expected, and also some "meh" features that I would have thought people would have wanted. You can see the end result in the feature set of the HPA-1. :)
I'm sure I'll have a market survey in the future - especially now where TCA is up and running and I can ask my customers directly for their preferences. That said, there's a lot of information in the previous survey, so I think I have a pretty good idea of where to go from here.

I love my HPA-1, this is what this section of the forum is about, from a performance perspective and its size it is one of my favorite amps. The amp has plenty of power for Single-ended use for most headphones. It finally made AEON FLOW Open Headphones enjoyable and not muddy, which is low impedance and low sensitivity headphones which creates a current pig. It is also great with the Ananda, RAD-0, HD-H650, and ELEX.
I'm glad you like it. Thanks for sharing.

When tom ready to take on larger XLR amp I know it will be great. He is an analog designer and magician at it.
Thank you. :)

Personally I love to see what he would do with DAC like AKM4490 since it analog section ( power and pre-amp) I care about. Topping D90 has a nice design, but it would be interesting to see what Tom would change.
You can always see the analog performance of the MiniDSP SHD. I'd probably tweak the circuit a bit from what I designed for them, but it should at least give you a general idea. I'd go without the DSP and sample rate converter, of course, so I'm pretty confident the jitter performance of any DAC I design would be better too.
I'll have a DAC eventually. The main challenge there is that it needs to support USB in a graceful manner. It's unfortunately not as simple as "just use XMOS and be done". The XMOS chips are (pretty kick-ass) microcontrollers. It would be nice if I could use them in a way that would allow them to handle the UI as well as the USB audio stack. I don't like the idea of having multiple microcontrollers to program if one is enough.
Anyway. There's some learning there that needs to happen. That's ok. I like learning. :)

Tom
 

tomchr

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@kn0ppers it is an expression, It means he is a very good analog engineer.
That's how I read it as well.

You need to talk to SPL why they want that much headroom in their Opamp. As I said it not just headphone amp
You also need to ask them to define "headroom". It's a meaningless marketing term as far as I'm concerned.

I meant the AKM4499 it was a typo.
The AKM4497 and AKM4499 (isn't that just a multi-channel 4497?) are incredibly expensive. $60/each in quantity! That said, it would certainly make for a nice "endgame" DAC.

Tom
 
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"The main challenge there is that it needs to support USB in a graceful manner. It's unfortunately not as simple as "just use XMOS and be done". The XMOS chips are (pretty kick-ass) microcontrollers. It would be nice if I could use them in a way that would allow them to handle the UI as well as the USB audio stack. I don't like the idea of having multiple microcontrollers to program if one is enough.
Anyway. There's some learning there that needs to happen. That's ok. I like learning. :)"

Tom[/QUOTE]

XMOS XU208 is an interesting chip, I have seen a couple of weird implementation like companies xDuoo XD05 plus, who bolted on USB-C connector without put-in in the USB-2 to USB-C outboard converter chip or logic. So you need special USB-C to USB-C OTG Audio cables or use USB-C to USB-A to USB-A to USB-C converter. This for both Power and DAC.

It was interesting to see these guys were a spin-off from Graphcore ( who are building big AI chips used at Microsoft Azure, they raised $310 million to date ) They also are building a deep learning accelerator but for the IOT market.

As you can see the Power side of the XDO5 PLUS is a little more hungry. This has AKM4493 DAC, also you can roll your own opAMPs if want, stock is dual Texas Instruments OPA1612.
IMG_9785.jpeg
 
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That's how I read it as well.


You also need to ask them to define "headroom". It's a meaningless marketing term as far as I'm concerned.
Yes it is, I have talked to Guitarist, in there world it really how well amp performs before it distorts, they will hit amp with cascading gain via pedal, some time for Solo they just want Volume lift and not have amp crunch up like Marshell or Vox when pushed. Vs Amps like Hiwatt or Two Rock especially 100-watt Classic Reverb or Fender Twin, this is just another world that does like distortion, and other attributes

Yes I am teaching my kids to play Guitar : )

IMG_9878.jpeg


The AKM4497 and AKM4499 (isn't that just a multi-channel 4497?) are incredibly expensive. $60/each in quantity! That said, it would certainly make for a nice "endgame" DAC.
Tom
AKM4499 has a number of new changes over the 4497 to better compete with Cirrus logic DAC, but yes it is a 4 channel DAC.
https://www.akm.com/content/dam/doc...dio-dac/ak4499eq/ak4499eq-en-productbrief.pdf
https://www.akm.com/kr/ko/products/audio/audio-dac/ak4499eq/

I picked up the Topping D90 to check it out. they run it just two-channel
 

kn0ppers

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@kn0ppers it is an expression, It means he is a very good analog engineer. I am an engineer I get it, I build super-computers and high-performance GPU's for my day job.

You need to talk to SPL why they want that much headroom in their Opamp. As I said it not just headphone amp
I know what you were saying, I just think audio is already mystified enough, so no need for more magic. I do agree that some parts of engineering heavily rely on experience and that for example laying out a PCB is probably as much of an art form as it is science. And Tom surely knows how to lay out his PCBs like works of art, so do you probably if you design GPUs.

Regarding the Phonitor: It is, according to them, "just" a HeadAmp/PreAmp with a DAC and some more advanced controls. Nowhere can I see anything that suggests this device is supposed to be more than that. But yeah, it has lots of power and enormous voltage swing capability. The VU meters are definitely an eye catcher, I personally like them a lot. I'm sure the SPL guys know what they are doing and have reasons for their decisions.

Also I didn't want this to turn into a shoot-out about who is an engineer and who isn't and who does the most complicated stuff for work, because I can't compete in that regard. I just wanted to point out that I have a basic understanding of the concepts that matter in electronics, although I am not an electrical engineer. I know enough to know how little I know, if you want to put it that way. Just thinking about return current paths on slightly more complex circuits gives me a headache... . I wanted to make a little DIY buffer months if not even a year ago, now I'll end up buying the one Tom made because I am so unsatisfied with my own attempts. His has tested performance, mine still only exists on a dirty breadboard and smells of nasty flux.

@tomchr

Fair enough, I already suspected you have plenty of data to work with. Have you thought about coming to the Munich audio expo / CanJam Munich and bringing the big amp at some point in the future? I haven't been there yet but it has long been on my list.
 
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@kn0ppers it is ok... I am not offended. Sometimes it good to get away from this and work, I spent the afternoon with my son and best friend and his son at Circut fo the Americas for Lone Star Le Mans. Nothing makes me forget all this stuff more than watching him smile from ear to ear. Most import for him beyond seeing the Ferrari's, Porsche's and Austin Martin's ( which was doing very well today), but watch him as saw the new Corvette C8.R and just beam with excitement.



DSC_4279.jpeg



IMG_9959.jpeg
 
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tomchr

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Fair enough, I already suspected you have plenty of data to work with. Have you thought about coming to the Munich audio expo / CanJam Munich and bringing the big amp at some point in the future? I haven't been there yet but it has long been on my list.
I think I'll practice with RMAF, Canjam Chicago, and maybe the Toronto Audio Fest first. :) They're the 1st, 2nd, and 3rd weekend in October ... and I'm thinking of driving. It's "only" 7600 km... :) We'll see. Ripping three weeks out of the calendar is hard on the business (and the body), so I may just do two of three.

For me to attend any show in Europe, I'd have to get my "show paraphernalia" into an airline-friendly or shipping-friendly format. I'm sure that can be done. It's "just" a matter of figuring it out. :)

Tom
 

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Finally... The measurements for the HPA-1 are now up. You'll find them in the Performance Graphs on the HPA-1 product page: https://www.tomchr.com/products/hpa-1

I'll go through and proofread tomorrow. I'm sure I can tweak a few sentences for clarity. The measurements can speak for themselves, though. I may add a few measurements as time goes on, but what's there is pretty comprehensive.

Tom
 

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Finally... The measurements for the HPA-1 are now up. You'll find them in the Performance Graphs on the HPA-1 product page: https://www.tomchr.com/products/hpa-1

I'll go through and proofread tomorrow. I'm sure I can tweak a few sentences for clarity. The measurements can speak for themselves, though. I may add a few measurements as time goes on, but what's there is pretty comprehensive.

Tom
Hi Tom

Can you add your own channel imbalance measurements?

Or are they the same as @amirm 's
 
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@tomchr

"As seen on the graph, it is only with 12 Ω load that the THD+N of the HPA-1 finally exceeds that of the Audio Precision APx525 audio analyzer."

Are you really trying to say "As seen on the graph, it is only with 12 Ω load that the THD+N of the HPA-1 finally exceeds the analysis limit of the Audio Precision APx525 audio analyzer."
 

tomchr

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Can you add your own channel imbalance measurements?

Or are they the same as @amirm 's
There is no way to measure the channel imbalance vs volume pot rotation in an automated fashion, so I suspect Amir turns the volume knob by hand and measures the amplifier's output amplitude. I can do the same, but you won't be able to overlay his results with mine and get the exact same graph. That said, the conclusion should be the same.

The timing of your question is excellent as I still have the HPA-1 hooked up to the APx525. I'll see what I can do about the channel imbalance vs pot rotation measurement.

Tom
 

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Updated the block diagram as well. The output stage is an inverting composite amp.
HPA-1_BlockDiagram.png

Tom
 

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OH... Did I mention that the HPA-1 was awarded Best of Show at the Florida Audio Expo? I should mention that... :)

Home Theater Hifi awarded the HPA-1 Best of Show: https://hometheaterhifi.com/feature...ls-concerts/florida-audio-expo-2020-coverage/

It's good to know that the amp passes subjective tests as well.

Tom
Well done @tomchr What you have done and are doing is great for the economy creating something from basically nothing and for as the Yankees say, "Make Canada great!" >@^_*@<
 

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tomchr

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Um. I think you may want to re-read the HT Hifi article. I'm pretty sure you missed a 'not' somewhere. ;)

Tom
 

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