HeadRoom Max headphone amplifier Maxed Out

Sidebar 2: Maxed Out

After my auditioning was over, I asked Tyll Hertsens to explain the evolution of the HeadRoom Max:

Hertsens: Part of the reason that I designed the HeadRoom Max was that we became aware of some parts that had become available for the module—the Burr-Brown 627, which replaced the Burr-Brown 604 op-amp, and the polyphenoline-sulfite film capacitors, which replace ceramic caps. I made the Home HeadRoom as good as I could—I actually think the 604 is a pretty good op-amp—but we were limited in that we had to use surface-mount components. Up until six months ago, the only surface-mount capacitors available were ceramic, and they just don't have the properties that poly-film caps do. With the advent of very-high-speed and large-oversampling-factor D/A converters, faster caps were required, and so the polyphenoline-sulfide film capacitor was developed. It's like a little sandwich of "interdigitated" film.

Phillips: Interdigitated?

Hertsens: Well, yeah. There's one contact at one end and another at the other end, and all the layers of capacitors are interdigitated—interleaved in between. They're high-speed with low ESR—all that good stuff.

Burr-Brown tells me that the 627 chip was developed by several different groups working in unison, but separately from one another. It was designed specifically to offer better audio quality, and it is really expensive. The chip costs $15 each when you buy it in quantities of 1000.

So we knew these parts were available, and we assumed we could build a better-sounding unit with them, but I thought, If this alone can offer an improvement, how much further can we go to make it better? The first step was to split the module in half so that the two boards aren't running next to each other—we physically separate them from each other. We don't pot the module either, because the potting compound has dielectric properties. We just leave it in air. We also put separate power supplies on it, changing the supply just a little to do so. We put a real nice potentiometer on the volume control and—to satisfy the audiophile community—we put an impressively massive front panel on it.

We didn't do anything divinely inspired, we just took the technology as far as it could go—to produce a product with an unusually high performance-to-price ratio.

I do worry about people using it with lesser sources. If they hear the shortcomings of the front-end, they may be tempted to attribute them to the amp itself.

Phillips: Is this your final word on headphone amplifiers?

Hertsens: Frankly, my feeling is that if anyone should build a $2000-$3000 headphone amp, it should be Sonic Frontiers or Counterpoint—which are companies who have licensed the module from us—not us. I have no desire to go beyond the Max.

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