Traditionally, headphone amps have been afterthoughts -- relatively low-cost circuits built into receivers, computers, portable media players, etc. After all, even with relatively insensitive headphones, the amp usually needs to put out no more than 50mW -- 0.05W -- to drive headphones to loud volumes with no audible distortion. But with headphones’ recent surge in popularity, and the concomitant growth in the number of hardcore headphone enthusiasts, many manufacturers have been putting serious design effort and resources into their headphone amps.

Simaudio’s Moon Neo 430HA ($3500 USD in base form, $4300 as reviewed with optional DAC) could arguably be considered the most serious headphone amp to date. There are more expensive amps -- Goldmund’s Telos HDA ($10,000) and Woo Audio’s WA-234 ($15,900), to cite two examples. But those amplifiers, despite their cost, are relatively simple, bare-bones products that lack some of the features enthusiasts may want, such as a variety of digital and analog inputs, balanced output, etc.

I can’t think of a feature the Moon 430HA doesn’t have that I would want. A partial list of what you get: balanced output on a single four-pin XLR and dual three-pin XLRs; XLR and RCA analog inputs; an optional DAC module that handles PCM at resolutions up to 32-bit/384kHz as well as DSD up to DSD256; an analog crossfeed circuit that helps get rid of that “sound in your head” effect; and RCA analog line outputs that let you use the 430HA as a preamp. The Moon Neo also has features that make it appropriate for high-end custom installations, including an RS-232 control port, an IR control port, and a remote control.

What’s missing? I guess Simaudio could have added Bluetooth wireless, but I suspect the people buying this amp wouldn’t care about that. Anyway, there’s a 3.5mm front input you can use with your smartphone or tablet; that’ll give you some level of convenience without the sonic degradation of Bluetooth.

Ultimately, though, you probably buy a $3500 headphone amp primarily for its sound quality, and based on how the Neo 430HA is built, it sure ought to sound good. Its power supply employs dual toroidal transformers to ensure there’s plenty of power on tap with minimal electromagnetic interference from the power supply. A large bank of 16 power-supply capacitors smooths out the power and provides extra headroom if and when the amp needs it. Seven separate voltage-regulation stages ensure that the power demands of one section of the amp don’t affect the others, and also help isolate the 430HA’s analog sections from its digital sections. Four of these regulation stages are fully discrete (i.e., they use separate transistors, not integrated circuits), and are claimed to produce virtually unmeasurable noise.

The amplification circuit itself is fully differential, meaning it’s essentially two amplifiers -- one each for the audio signal’s positive and negative halves -- laid out in a mirror-imaged arrangement. The advantages of this design are that it helps cancel incoming noise and it doubles the amplifier’s slew rate; i.e., the speed at which the amp can respond to incoming signals.

From the spec sheet, at least, the Moon Neo 430HA looks like one of the most impressive headphone amps ever created. Now it’s time to hear if all that high-end construction has yielded a substantial improvement in sound quality.

In the box

The Moon Neo 430HA includes the usual accessories you’d expect to find with a preamp: a power cord, a remote control, and a manual. There’s also a SimLink cable -- just a cable tipped with 3.5mm plugs that you can use to connect to other Simaudio components so they all turn on and off simultaneously.

The sample I received came with the optional DAC module installed ($800). My guess is that almost everyone who buys a 430HA will get it with the DAC. It’s a bargain, considering that it includes an ESS Sabre Reference DAC chip that can accept PCM signals up to 32/384 resolution, and that it can natively process DSD files up to quad bitrate, without converting them to PCM. (Yeah, I know, almost all DSD files have been processed through PCM anyway, but hey -- I’m just reporting here, I’m not the poster boy for DSD.) The DAC also includes two coax (RCA) inputs, a TosLink input, and a USB input.

I suppose if you already have a great DAC and just need the amp section of the Neo 430HA, you might want to skip the onboard DAC option; otherwise, it seems like a no-brainer.

Use

Operating the Moon Neo 430HA was actually more straightforward than other high-end digital preamps I’ve used because it doesn’t rely on menus. Everything is controlled through discrete buttons on the front panel, which made it fast’n’easy to make all the necessary adjustments. (The remote controls power, volume, input, and mute; I didn’t use it.)

One feature I haven’t yet discussed is the high/low gain setting, accessible via a front-panel button. The 430HA defaults to low gain, and even with the relatively inefficient HiFiMan HE-560 headphones (86.7dB at 1mW, by my measurement), that was more power than I needed. Maybe you’d need the extra 6dB of the high-gain setting for something like HiFiMan’s notoriously inefficient HE-6 model (I measured 81.1dB at 1mW); otherwise, this button can probably go unpressed.