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Tom Christiansen Audio HPA-1 Headphone Amp Review

tomchr

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Nah. He's just yanking my chain. In a friendly way. :)

See this discussion for context: https://www.audiosciencereview.com/...of-these-measurements-tortuga-ldr3-v25.10025/

LDR volume control embodies everything Tom is NOT looking for.
I've yet to see anything I like in an LDR volume control. They do offer the potential of better channel matching, but as you can see in Amir's measurements, channel matching is not an issue for me.

I make my design decisions based on science, engineering, and measurements of prototype circuits. I will occasionally add a feature or steer the design in a certain way so I can get a marketing blurb, but only if it can be done without degrading performance or increasing cost. Some manufacturers put more emphasis on marketing than I do. That's fine. We can all coexist and others are free to do things differently. The consumer will decide in the end. I commend Amir's efforts to make consumers more informed by making troves of data available.

Tom
 

Schackmannen

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What's the point of having balanced inputs on a device that doesn't have balanced outputs? Seems like a very odd design choice to me.
Balanced inputs basically eliminate the change of ground loops occurring whereas balanced headphone outputs provide no benefit other than double the output voltage compared to an equivalent single-ended output. Benchmark has some excellent articles on this topic:
https://benchmarkmedia.com/blogs/application_notes/balanced-vs-unbalanced-analog-interfaces
https://benchmarkmedia.com/blogs/application_notes/audio-myth-balanced-headphone-outputs-are-better
 

amirm

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What's the point of having balanced inputs on a device that doesn't have balanced outputs? Seems like a very odd design choice to me.
Balanced outputs are not useful for anything other than having a differential headphone amplifier that produces more power. If you have enough power, then having balanced out is of no value.

Balanced inputs on the other hand, guard against ground loops. This is extremely useful in PC or powered speaker environments where chances of a ground loop are high.
 

JohnYang1997

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Balanced outputs are not useful for anything other than having a differential headphone amplifier that produces more power. If you have enough power, then having balanced out is of no value.

Balanced inputs on the other hand, guard against ground loops. This is extremely useful in PC or powered speaker environments where chances of a ground loop are high.
Can we have a look at the measurement of this HPA-1 with unbalanced input?
 

tomchr

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What's the point of having balanced inputs on a device that doesn't have balanced outputs? Seems like a very odd design choice to me.
Balanced inputs are very handy with sources that have balanced outputs. Many pro level DACs have balanced outputs and as others have pointed out above, there are quite a few technical advantages of balanced signalling, including higher dynamic range and common-mode rejection. Balanced inputs were also rated as a more desirable feature than balanced outputs in my market survey.

I've yet to find a technical advantage of a balanced headphone output, on the other hand. You get higher output power for the same supply voltage (if the output driver can supply the required output current that is), but that's it.

So in my view a better question is: "What's the point of having a balanced headphone output? That seems like a very odd design choice to me." :)

Tom
 

miero

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Balanced output for headphones could also remove a ground wire acting like a long antenna for RF in the headphone cable.
 

JJB70

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Balanced headphones strikes me as another of those "we can't miss the bus" group think things for manufacturers, someone starts it, the usual subjective reviewers wax lyrical about it and suddenly the headphone hipsters have convinced themselves they need balanced headphones so manufacturers start including it whether it makes any sense or not because if they don't they risk losing ground in the market. The Benchmark article was published years ago and remains valid, Nwavguy also wrote some good stuff on the subject if I remember rightly.
 

BYRTT

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Balanced output for headphones could also remove a ground wire acting like a long antenna for RF in the headphone cable.
Could we imagine for a very low output impedance unit as HPA-1 (35 mΩ) stuff as that would have revealed itself more or less in some expanding/growing grass as frequence goes up into 32 bit tone test.
 

tomchr

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Balanced output for headphones could also remove a ground wire acting like a long antenna for RF in the headphone cable.
Sure. But it adds two signal wires that can act as RF antennas. I decouple headphone outputs with small ceramic caps right at the 1/4" phone connector for exactly that reason.

Tom
 

tomchr

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Balanced headphones strikes me as another of those "we can't miss the bus" group think things for manufacturers, someone starts it, the usual subjective reviewers wax lyrical about it and suddenly the headphone hipsters have convinced themselves they need balanced headphones so manufacturers start including it whether it makes any sense or not because if they don't they risk losing ground in the market. The Benchmark article was published years ago and remains valid, Nwavguy also wrote some good stuff on the subject if I remember rightly.
From what I understand the "balanced is better" myth started on Head-Fi some ten years ago. People started wanted balanced drive (or at least a 4-pin output), so manufacturers offered it. And why not? It's a ways of applying a "PROFESSIONAL" badge to a piece of equipment. "Our amp is a PROFESSIONAL amp! Look! It has a large and in charge connector on the front panel!! It must be good". There's probably some consumer psychology there...

If/when I make a large-and-in-charge amp, it'll have a 4-pin output on it too. After all, that's what consumers expect of a "serious" amp, so why not deliver it? :)

At least the 4-pin output does not degrade performance, unlike many other marketing-driven fads.

Tom
 
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I was wondering if you could add a Distortion vs. Power @ 13 or 16 Ohms? With some newer planners like Dan Clark Aeon Flow, Aeon X, Aeon 2, Audeze LCD-1. All AEON's are 13 Ohm and with 92dB/mW Closed-back("AFC"), 94dB Open-Back("AFO") they need a fair amount of current. Audeze LCD-1 16 Ohm 99 dB/mW

Ran a ruff calculation the Aeon ( AFO & AFC) they need more current then Hifman HE-560 to drive them properly, just want to see how amp handles this class of load since we are seeing headphone in this design space.

@tomchr already put in pre-order.
 

tomchr

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I openly wonder why manufacturers design their headphones with such low impedance. I fully understand that USB-powered sources that run on 3.3 V or 5 V can't provide much voltage swing, so manufacturers have lowered the impedance of their 'phones accordingly. But 13 Ω?? That's just dumb!
The saving grace is that the 'phones tend to be high-efficiency, so they'll blow your ears (literally!) even with 100 mW applied. 100 mW into 13 Ω only requires 125 mA (peak) of clean swing, which I'm confident the HPA-1 can deliver. That said, I would also expect the THD to be a touch higher at the lower impedances than at, say, 300 Ω.

Anyway. It's not the first time the market has disagreed with good engineering, and ultimately the market pays the bills. So I'll add a 12 Ω tap to the headphone dummy load I'm building and measure. :)

And thanks for your preorder. There are 13 left on the preorder deal. On January 15th, I'll increase the preorder price to $849. I expect to be able to ship before the end of the month. Once the HPA-1 is in stock, the final price of $899 will kick in. As noted in my FAQ, I will not have a sale aside from the preorder sale. The preorder discount is my way of thanking those who are wiling to support me while the amps are in production. Those who have waited the longest have received the largest discount. Some have waited since September! Thank you for your patience.

Tom
 
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Yes, you hit on the issue I was concerned with is Peak current and also Instatnous Peak currents. Yes, I had about ~100 mA for 110 dB voltage @ ~1.28 Volts.

When looking at other planner are relatively low ohm's relative to the dynamics based headsets

Hifiman
  • Ananda is 25 Ohms with 103 dB, As you can see still l low Ohm
  • Arya is 41 Ohms with 91.2 dB, the YouTube reviews favorite, power-hungry
  • HE-1000 SE 35 Ohms @ 90 dB
  • HE-560 45 Ohms @ 90 dB
  • HE-4xx 32 Ohms @ 93 dB

Audeze
  • LCD-1 16 Ohms @ 99 dB
  • LCD-X 20 Ohms @ 103 dB
  • LCD-2C 70 Ohm @ 101 dB <- exception
  • LCD-3 110 Ohm @ 101 dB <- exception
  • LCD-4 200 Ohm @ 97 dB<- exception
Dan Clark Audio/Mr Speakers
  • Ether C 23 Ohms @ 90 dB
  • Ether Flow 1.1 23 Ohms @ 92 dB
  • Ether C Flow 1.1 23 Ohms @ 90 dB
  • Ether CX 23 Ohms @ 92 dB
  • Ether 2 16 Ohms @ ~92 dB
  • Aeon Flow
    • Open 13 Ohms @ 94 dB
    • Closed 13 Ohms @92 dB
  • Aeon X 13 13 Ohms
    • Open 13 Ohms @ 94 dB
    • Closed 13 Ohms @92 dB
  • Aeon 2
    • Open 13 Ohms @ 94 dB
    • Closed 13 Ohms @92 dB
Rosson Audio Design
  • RAD-O 29 Ohms @ 98 dB
Sendy Audio
  • Aiva 32 Ohms 94 dB
Dynamics
  • Focal Elex 80 Ohms 104 dB
  • Sennheiser HD 6XX 300 Ohms 107 dB
  • Beyerdynamic DT880 Pro 600 Ohms 96 dB
  • AudioTechnica MTH-50x 38 Ohms 99 dB
RE: Updated with other ratings from earlier
 
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solderdude

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King of low impedance planars is the Verum1, rated at 8Ω but measured around 6Ω
 
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Celty

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Balanced outputs are not useful for anything other than having a differential headphone amplifier that produces more power. If you have enough power, then having balanced out is of no value.

Balanced inputs on the other hand, guard against ground loops. This is extremely useful in PC or powered speaker environments where chances of a ground loop are high.
True of course. For me using XLR for both in and out does offer both advantages, as having the additional power on tap when needed is great. With three gain level settings, there really is no downside for me.
 

tomchr

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No doubt a future even-higher-end TCA headphone amp (yet to be designed or even considered) will have higher output power, higher output current capability, and 4-pin XLR output. Mostly for marketing reasons, but also to some extent for performance reasons. It'll also be larger and heavier so that it will appear more powerful and "serious"; and will be even stronger associated with quality than its smaller brothers.

I doubt the 4-pin will be balanced out, though. I'll probably route the same signal to the 1/4" jack and 4-pin XLR and just design the amp to provide the higher swing needed for the magic 5 W into 50 Ω that many use as the gold standard. As mentioned previously, there's no technical advantage of a differential output, and I would like to avoid having separate specs for the 1/4" and 4-pin outputs.

Meanwhile, those of us who have more reasonable demands for output power will continue to enjoy the HPA-1.

BTW: Those of you in the Seattle area now have the opportunity to experience the HPA-1 in person. A friend of mine owns Lawrence & Scott. They deliver high-end lighting solutions and are branching out into other areas of luxury/high-end goods with my HPA-1. I figured my friend's experience with high-end goods and his extensive audio experience (he used to review for one of the British hifi magazines, so he's heard a lot of gear) would be a good match for me. You can find Lawrence & Scott in the Georgetown area, and their website here: https://www.lawrenceandscott.com/the-good-life/
Please contact me - or them directly - if you would like to schedule a listening session.

Tom
 
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