UcD180HG HxR: A Leading Class D Power Amplifier by Hypex

My Do-It-Yourself SEAS A26 speakers turned out to be a big success. Still I found clarity lacking and the sound stage compressed during complex musical passages. Moving down to the weakest link in my setup, my Marantz NR1602 amplifier, I decided to build an audiophile DIY power amplifier: a stereo Hypex UcD180HG HxR with an SMPS400A180 switching mode power supply.

Selecting the UcD180HG

Having decided to build my DIY power amplifier, I spent quite some time deciding on which one. Deciding factors were the following:

  • Heat dissipation. To obtain an acceptable Wife Acceptance Factor, I realized that the complete package should fit in my media furniture, in a slit beside my slimline Marantz amplifier with little ventilation. So I quickly turned to class D amplification, renowned for its high efficiency.
  • Brand. This was a no-brainer. When it comes to class D technology, Hypex reigns supreme. Catering to renowned brands such as NAD and Marantz for their high-end series, they also provide the DIY community with top-of-the-line amplifier modules and power supplies.
  • Power. The SEAS A26 8Ω woofer is rated for 80W long-term and 300W short-term, while its 6Ω tweeter is rated a whopping 100W long-term and 250W short-term. I mostly listen at -40 dB so I don’t really need that much power, though I appreciate the headroom for sudden loud passages. Hypex’ UcD180HG delivers 120W into 8Ω loads and that seems fine to me.
  • Cost. Hypex carries two amplifier topologies: the best-in-class NCORE and former champion UcD. Most prominent differences are the order of the feedback loop, discreetness of the input buffer, and ultimately, cost. The difference is not subtle: €325 for a NC400, €100 for an UcD400HG, and €70 for the Hypex UcD180HG that would suffice power-wise.

Hypex UcD180HG HxR

My pockets led me to the Hypex UcD180HG with HxR voltage regulators. Power stability is key in audiophile applications. And these have a Power Supply Rejection Ratio of a whopping 110 dB!

Let us put this in perspective. Many well regarded regulators specify their maximum PSRR at 80 dB or so. These boys are 30 dB better — that is 31,6 times higher rejection. At a €30 premium for an HxR, that is exactly what those UcD’s are getting.

Powering the UcD180HG

Having gone with Hypex amplifier modules, it only made sense to also settle for a Hypex power supply. Hypex recently moved from linear power supplies to switching mode power supplies made specifically for audiophile applications.

The entry-level Hypex SMPS400A180 delivers a maximum of 400W at 20Hz or 600W into a resistive dummy load. That’s more than enough for two UcD180HG amplifier modules.

Hypex SMPS400A180

Yet here I spent a long time deciding whether I would opt for a single, shared power supply or two separate ones. The latter would offer more headroom and improve stereo crosstalk. Alas, at over €100 a piece (and forgoing more complex grounding in a single chassis) I settled on a single SMPS.

Chassis and cabling

Hi-Fi2000 GalaxyI got a nice black anodized Hi-Fi 2000 Galaxy chassis to fit it all in. As for cabling and connectors, the Hypex webshop is a great resource. I got the gold-plated loudspeaker binding posts and RCA connectors, signal cables and cable sets.

Invaluable too are Hypex’ application notes on insulation and signal wiring. Reading the paper on “audio ground” was especially enlightening. It is a bit of a wonder actually to be seeing so many grounding and humming issues when the solution is so clear and easy.

To get everything off the ground, I decided on a Class II insulated design and ordered a two-prong IEC inlet and Schuko cable.

As speaker hookup wire, I still had some Oehlbach Twin Mix One loudspeaker cable lying around. Refer to the UcD and SMPS datasheets to understand what should be wired where. This wiring diagram, too.

Hypex Interlink ST RCA-RCA

Finally, I bought two standard Hypex RCA-RCA interlink cables. At nearly €100 each I thought they were pretty steep. The high-grade variants would even be over €160 a piece! I am not one for the fairy dust cable camp; when equipment is stacked or directly next to each other there really is very little in the way of EMI. Especially in a home environment.

Bypassing input capacitors on the UcD180HG

Unlike the NCORE, the Hypex UcD180HG modules are not DC-coupled. Meaning they have capacitors in the input signals to block direct current from being amplified and potentially damaging any speakers.

Sounds good, no? Actually, probably not — most modern sources do not output dangerous DC offsets. On the flip side, capacitors in the signal path do degrade audio quality.

Subjective preferences aside, I am all for “as little as possible components in the audio path” to maintain neutrality. Components will influence the signal one way or another — coils and capacitors especially. My ideal amplifier is neutral. It reproduces the signal faithfully, as if it were a wire with gain. Even the most boutique capacitor will color the sound.

Moral of the story is: I bypassed the input capacitors by soldering a jumper wire on the back of the boards. But not before listening on a bench setup, before mounting them into a chassis. And indeed, this modification does breathe air and dynamics into the sound.

Putting it all together

I sent the chassis backplate to Schaeffer in Germany to have it milled for connectors and labeling. Their Front Panel Designer software rocks. I think I got the plate back in a week or so, screw holes tapped and all. All connectors fit to a tee.

In the back panel I had also design through-holes to mount the Hypex UcD180HG heatsinks. Applying a small amount of thermal paste between the heatsinks and back panel, the modules now have the entire chassis to dissipate heat.

The layout of the chassis is such that there is no crossing of audio signal and power supply wires. Regardless, I diligently braided all cables for minimum electromagnetic interference, and moved the switching-mode power supply as far away from the amplifier modules as possible.

The SMPS board requires one metal spacer that should be connected to the chassis as a ground breaker. As the anodized aluminium does not conduct, I sanded the contact point until I measured 0Ω between that point and the RCA connectors.

Real happy with the result! One bit of self-criticism: I should have used heat shrink tubing on the mains power cable.

Listening Results

I built this amp in a quest for greater clarity and wider soundstage. And surely, the Hypex delivered.

First is an absolutely powerful, controlled bass. It is not that it is tighter or more bellowing, but something harder to put into words… a powerful rendition of what was recorded, keeping the woofer in check where it otherwise would have strayed ever so slightly of the amp’s signal.

This bass control is well spoken of on various forums but is something to be heard for yourself. Technically, it is rooted in Hypex’ unique load independence over the full range with heaps of global feedback. And it works.

The SEAS A26 can be driven to pretty hefty levels and the Hypex UcD180HG does so seemingly without effort. Not just the bass but across the board it is clear that this amp keeps the drivers exactly where it wants them to be.

Finally, noise is a thing of the past. Dial the volume knob all the way up without hooking up a source — no white noise, black as the night. And as for A/B testing: take out this power amplifier, and notice the hiss on the Marantz.

Only downside to every audio upgrade? There is always a new weakest link to upgrade. Onto replacing the Marantz with a proper DAC and line stage!