TCA HPA-10 headphone amp

[tomchr]

Nimble, yet powerful: The Tom Christiansen Audio HPA-10 easily fits in the palm of your hand, yet delivers 1.25 W into 32 Ω and 250 mW into 300 Ω at vanishingly low distortion. The THD+N is below the -112 dBc noise floor of my APx525 and preliminary measurements indicate that the THD is below -130 dBc (100 mW, 300 Ω). The multi-tone IMD clocks in at about -145 dBc (100 mW, 300 Ω) and the noise floor measures 1.6 µV RMS (A-weighted, 20 Hz - 20 kHz). Oh, and it sounds good too...

The HPA-10 is designed, assembled, and tested in Canada. The raw circuit board comes from Toronto and the assembly and test is done in Calgary. All electronic parts are sourced via authorized distributors in the USA and Canada. The chassis is manufactured in Japan.

I opened up for pre-orders today. The pre-order pricing of $439 includes a nice early adopter discount. The discount will end and the final price of $469 will kick in by 23.59 MST on November 30th, 2020. You can read more about the HPA-10 and place your pre-order here: » TCA HPA-10 Product Page.
Note that TCA now offers fast shipping via FedEx and UPS (as well as the slower Canada Post) at very competitive rates.

The HPA-10 includes many newly released components and the availability of these components is rather limited at the moment. As result, the first batch of HPA-10 will only be a total of 50 amps. I expect them to move pretty quickly once I let more of the world know that I have these. I will do my best to keep up with demand.

The measurements below are of the prototype. I'm making a few layout tweaks for the final version, which should improve performance slightly. That's also why I haven't posted a full suite of measurements yet.

Tom

 

[Doodski]

That amp must be dead silent when cranking it up.

 

[tomchr]

If you don't provide any signal to it, it's very silent indeed.

Tom

 

[solderdude]

The gain is 10dB (3.2x) meaning with a 2V or 2.1V output DAC you cannot clip the amp on these DACs.
8.7V (250mW in 300Ohm) thus can't be reached with 'normal' DAC, only 150mW in 300 Ohm.
Of course this will be enough for most cases

Impressive design..how's the THD in 32 and 20 Ohm ?

 

[tomchr]

The amp requires 2.0 V to clip into 32 Ω. 2.7 V RMS is needed to make the amp clip in 300 Ω. I can certainly make the gain higher, but that gives you higher noise. It also makes the volume control really touchy. I don't think it's a good user experience when the volume goes from whisper to jet engine if you breathe on the volume knob. I prefer to operate with less than 40 dB attenuation on the volume knob (so in the 9-12 o'clock range). But I'm sure some will perceive the amp as "weak" because they have to turn the volume past 9 o'clock to make their ears bleed.

The THD+N does start to creep up a bit at the lower impedances. The HPA-10 drives 32 Ω and 20 Ω just fine, though. See below.

My goal with the HPA-10 was to make a small, portable amp that provides stellar performance and can be sold for less than $500 including shipping. Hitting that price point without compromising performance was a significant (but fun!) challenge, actually. The only place I had to give on performance was on the output current of the amp. The HPA-10 provides 250 mA, peak. The HPA-1 provides over twice that.
I hesitate to label the HPA-10 as "optimized for high-impedance headphones", because, as you can see below, it drives 32 Ω and 20 Ω headphones with distortion well below audible. But if you press me hard enough, that's probably the answer you'll get.

Tom

 

[LLL]

Capital!

Well done, Tom. I expect nothing less from you.

 

[solderdude]

The amp requires 2.0 V to clip into 32 Ω. 2.7 V RMS is needed to make the amp clip in 300 Ω. I can certainly make the gain higher, but that gives you higher noise. It also makes the volume control really touchy. I don't think it's a good user experience when the volume goes from whisper to jet engine if you breathe on the volume knob. I prefer to operate with less than 40 dB attenuation on the volume knob (so in the 9-12 o'clock range). But I'm sure some will perceive the amp as "weak" because they have to turn the volume past 9 o'clock to make their ears bleed.

The THD+N does start to creep up a bit at the lower impedances. The HPA-10 drives 32 Ω and 20 Ω just fine, though. See below.

My goal with the HPA-10 was to make a small, portable amp that provides stellar performance and can be sold for less than $500 including shipping. Hitting that price point without compromising performance was a significant (but fun!) challenge, actually. The only place I had to give on performance was on the output current of the amp. The HPA-10 provides 250 mA, peak. The HPA-1 provides over twice that.
I hesitate to label the HPA-10 as "optimized for high-impedance headphones", because, as you can see below, it drives 32 Ω and 20 Ω headphones with distortion well below audible. But if you press me hard enough, that's probably the answer you'll get.

Tom
View attachment 94346View attachment 94345

 

[deafenears]

Well done! Any pics of the internals to share with us?

 

[kn0ppers]

There is a block diagram that should answer most of the questions one could have about the internals

 

[tomchr]

Well done! Any pics of the internals to share with us?

No. Not yet. I'll wait until I have the final boards.

Tom

 

[Ilkless]

The chassis is manufactured in Japan.

Takachi? I would have thought Hammond is a domestic option but I guess with a company their size much of their enclosures are OEM from China and you can't really tell which is which.

 

[tomchr]

Hammond doesn't have anything compelling. Not that I'm aware anyway. I do have a high-end Canadian manufacturer in mind for when I go upmarket, but I'm afraid to ask how much they charge. I've also explored some local options. There are several machine shops in Calgary that market themselves as "precision" fabricators. Their idea of "precision" is that they can make a powder coated industrial control panel for the oil & gas industry that fits the specified bolt pattern if you beat on it hard enough. That's not what I need.

Tom

 

[Kadent]

Would there be any performance gains if you were to have designed it to operate via AC voltage rather than DC?

Kaden

 

[tomchr]

Hey, Kaden. Welcome to ASR.

I was actually hoping to use AC power as that makes it easy and inexpensive to generate the split supply used within the amp. All you do is to use a voltage doubler, possibly with a pair of voltage regulators after and you have a nice bipolar supply. The drawback is that you tend to get higher mains hum as the rectification creates a lot of mains harmonics. I often see mains harmonics up to 1 kHz above the noise floor.

The main advantage of using AC voltage is that it's dirt cheap and simple. Unfortunately, it is extremely difficult to find an AC wall wart that can provide enough power from a North American distributor. Even the low-powered ones are going away fast. I looked high and low and had my suppliers look as well. We all came up empty. One "possibility" was to have Triad Magnetics design a custom transformer. Only $20k in setup costs...

I believe the reason is energy efficiency. The AC wall warts simply can't meet the Level IV energy efficiency requirements. It's pretty common for small power transformers to consume 1-2 W with no load connected. That may not sound like much, but count the number of chargers and wall warts in your home and recall that these devices are often left plugged in 24/7 and it adds up to a lot of wasted energy.

Of course, I could do what some other manufacturers do: Import cheap transformers from China. I found the Chinese manufacturer that a well-known headphone amp company uses. If you buy 2500 transformers (that's the minimum order quantity!), you can get them for less than $5 each. Of course, that also requires an investment of $12500... I did consider that option, but decided against it.
The energy efficiency requirements were put in place for a reason. I believe manufacturers, such as me, should work to minimize our environmental footprint, including the environmental impact of the use of our products. I also didn't want 2500 transformers sitting in my garage... It's probably only a matter of time before you're no longer allowed to sell them for residential use - assuming you're allowed today.

So I went with a 10 W AC/DC wall wart that provides 5 V. That goes to a DC/DC converter within the amp itself. Interestingly, there's quite a bit of difference in performance between AC/DC converters and this difference can be measured on the amp output. Some of the cheaper AC/DC wall warts result in a higher noise floor and higher mains hum at the output of the amp. So I went with a more expensive AC/DC wall wart than I'd hoped for. Oh, well. I would rather have a product that's a bit more expensive and performs well than one that's cheaper and doesn't perform well.

Anyway. That was probably a longer answer than you expected, but I wanted to shed some light on my design and decision-making process.

Tom

 

[Kadent]

Tom

Always appreciate your explanations. Now that you explained your reasoning I do agree with the power waste and inefficiency involved with those lower quality transformers.

Another way that I know might work for these smaller size amps are to use a negetive rail generator, though the downside with those is that they often can’t supply with enough current to power the circuit.

You mentioned using some newer OP amps in this design, please correct me if I’m wrong but some of the newer designs can run off a single supply, though I’m not sure if that hinders performance.

Edit: Is the HPA-10 running internal regulators or running one of those AC/DC transformers that have internal regulators?

Awesome job on this new smaller footprint amp, I’m really digging it!

Kaden

 

[amirm]

Anyway. That was probably a longer answer than you expected, but I wanted to shed some light on my design and decision-making process.

Tom

I love longer answers. Gives us a lot of insights and balancing act designers go through to produce hardware products.

 

[tomchr]

Another way that I know might work for these smaller size amps are to use a negetive rail generator, though the downside with those is that they often can’t supply with enough current to power the circuit.

I did look at inverters. That was my first option, actually. But I wasn't able to find a circuit that would provide the needed current with a low enough ripple voltage at a price I liked. If you don't need much current or you can accept high ripple voltage, a charge pump may work well for you. There are plenty of ICs to help you with that.

I also considered a couple of split-rail converter ICs. TI has one that on the surface looks like a good fit, but it had really bad regulation on the negative rail, so I quickly abandoned that idea. LT/ADI has a nice chip, but the total solution cost would exceed that of a monolithic DC/DC converter, so I went with the 5 V in -> ±15 V out monolithic DC/DC converter.

You mentioned using some newer OP amps in this design, please correct me if I’m wrong but some of the newer designs can run off a single supply, though I’m not sure if that hinders performance.

You can run any opamp on a single supply, but you then need AC coupling caps on the audio signals. There's nothing wrong with that, they make it harder to ensure a click/pop-free startup and power-down. Recall that the cap needs to change to VCC/2 and that charge has to come from somewhere. You also need to create a clean "ground" reference at VCC/2. That's pretty difficult, actually, especially if you also want a reasonable start-up time and good power supply rejection. My first prototype was single-rail, actually. It provided good THD but its mains hum was higher than I'd like due to the artificial ground reference.

Edit: Is the HPA-10 running internal regulators or running one of those AC/DC transformers that have internal regulators?

The HPA-10 takes 5 V DC in from an external AC/DC wall wart and uses an internal DC/DC converter to create ±15 V.

I did consider pulling the power supply inside the chassis and have the HPA-10 run on mains voltage directly. There are plenty of good AC/DC switching bricks. I use a pair in my HPA-1. Unfortunately this requires a significantly larger chassis as I would need to provide a safe creepage distance between any point connected to the mains and anything that can be touched by the end user. That would make the amp more expensive and less compact, so I scrapped that idea.

Awesome job on this new smaller footprint amp, I’m really digging it!

Thank you!

Tom

 

[Nemo]

I do not have a need of a portable version of my HPA-1, but it is SO good (clear, transparent, stupendous built) that I still feel tempted: @tomchr keep up the good work!!

 

[tomchr]

For once the metal and the packaging materials arrive ahead of the electronics. The electronics should be here tomorrow afternoon and I expect to start shipping by Wednesday afternoon or Thursday morning.

Tom

 

[groovybassist]

I have Tom's TCA HPA-1 and a Neurochrome Modulus-286 built by Tom, and both are outstanding products. I'm sure Tom's engineering chops have turned out a great portable headphone amp.