Introduction

The life of an audio hobbyist and reviewer can be a painful journey. Just two weekends ago, I managed to destroy the USB input of my beloved Gustard X20 DAC :(

It happened while I was doing a comparative review between the Hifiberry Digi+ Pro and the Gustard USB input. Although my DAC displayed the correct sampling rate, it produced no sound at its outputs. Both XLR and RCA were essentially dead.

I thought only the venerable Texas Instruments PCM27xx chipsets of yesteryear were prone to premature failure. (I fried a few USB-to-SP/DIF converters in the past, but that’s another story.)

Replacing the built-in USB card turned out to be too costly, plus I didn’t want to deal with the hassle of sending the unit back to China for repair. It certainly wasn’t a big dealbreaker because I’m totally satisfied with the Hifiberry Digi+ Pro anyway (and even the older Digi+ for that matter).

As an audiophile, I felt the itch to try out the I2S input of the Gustard DAC anyway and was thinking of getting an external DDC (digital-to-digital converter), which appeared to be all the rage.

I know I could have hacked my Raspberry Pi to output I2S directly, but I didn’t want polluted clocks feeding my Gustard. Who knows how much extra performance you can extract with I2S instead of SP/DIF?

Gustard actually offers the U12 converter, which received fantastic reviews.

However, I heard great things about the Singxer SU-1 in various audio forums. Readers claimed it was the best thing since sliced bread. After seeing spy shots of the internal components, I immediately decided to buy one.

Features

The Singxer SU-1 has a single dedicated purpose: it takes the USB output of your computer or smartphone (Android is supported via OTG cables; iPhones probably work too, but I haven’t tried it) and translates your music collection into a pristine digital output signal for your DAC.

Clock generation is performed by high-precision Crystek femto clocks. A similar implementation could be found in top-of-the-line Auralic Aries streamers at the time.

Well, those cost quite a bit more, of course.

This means you still need a DAC, of course. The Singxer SU-1 is great for folks with a music server setup wishing to enjoy the best audio quality over USB with no dropouts or interference and with galvanic isolation.

With the Singxer, you’ve got these bases covered. It also eliminates the “need” for expensive add-ons like reclockers or jitter bugs… you get the point.

What’s really impressive about the Singxer unit is its massive processing power thanks to the xCORE chipsets. I’m not sure how much these contribute to the overall sound, though.

You can choose between coaxial or BNC SP/DIF plus AES/EBU outputs, but I personally find the I2S output to be the most appealing.

Like with typical professional-grade audio gear, you can slave external digital devices to the Singxer. A Word Clock output does the magic here.

A nice touch indeed, although probably not that useful for home audio purposes.

The Singxer SU-1 is capable of outputting up to a 384 kHz sample rate over PCM, and even DSD256 is fully supported. I tried almost every combination of sample rates and couldn’t find any limitations.

Because I was afraid of losing the warranty, I didn’t open my unit. But judging from interior shots circulating on the internet, the Singxer is a brilliantly engineered device featuring a 4-layer circuit board, low-noise voltage regulators and a real toroidal transformer by Talema.

If it were made in the United States or Europe, I would expect it to cost at least twice as much. I’m not sure who the designer(s) are, but it certainly doesn’t look like a crappy audiophile DIY project.

The Singxer is built extremely well and feels like a premium product. It shipped with a decent USB cable.

Drivers are generally not needed for macOS or Linux users. Windows users could download the appropriate drivers. Hopefully, the Windows Creators Update will finally eliminate the need for drivers. We’ll see.

What the Heck Is I2S?

Many audiophiles confuse I2S with a standardized external interface, but that’s not the case.

I2S was originally engineered by Sony and Philips back in the 80s as a means of transmitting raw PCM data to the DAC chip itself.

The I2S bus basically consists of a word-select line with L/R channel indication, a bit clock and a data line. There’s no middle-man PLL or SP/DIF receiver circuitry.

Instead, you need to make sure you send data to the DAC chip in the correct format. If you screw this up, you get white noise or strange whining noises.

And because you are sending high-frequency digital signals in the MHz range through a cable, you’d better have a well-shielded connection.

HDMI works very well for this type of transmission. I strongly recommend a short HDMI cable.

You don’t need to purchase any fancy “audiophile” cable, just a reliable one. I personally used a cheap Amazon Basics HDMI cable, and it worked flawlessly.

Singxer allows you to customize its data output lines using a simple DIP switch on the bottom side.

My Gustard X20 worked right out of the box, and I suspect most Chinese DACs will work without adaptations. I can confirm that the smaller X12 DAC works with the Singxer SU-1 USB, too.

However, you should definitely consult the manual of your DAC for the correct pinout of its HDMI port.

Sound Quality Improvements and Conclusions

So, does the Singxer SU-1 improve the sound quality as a front end to your DAC?

I hooked up my Raspberry Pi via USB to the Singxer and went straight via HDMI cable to the Gustard I2S input.

Everything worked right out of the box.

Be prepared for some occasional clicking noises when you switch to another track encoded at a different sample rate. It’s not really a big deal. I cannot fault the Singxer or the Gustard for this, as the I2S interface basically takes precedence here.

Listening through my STAX SR-007 MK1, I felt an immediately noticeable improvement in the soundstage.

Instruments in Yo-Yo Ma’s “Appassionata” seemed further away from my ears, and during quiet passages I could pick up more cues from the recording ambience.

This experience was easily repeated with other recordings. When I switched back to the Hifiberry Digi+ as the source, those small details weren’t as apparent anymore.

I wouldn’t be telling you the truth if I claimed that I suddenly noticed massive changes. It’s those subtle details that make my listening sessions even more enjoyable.

One thing that really surprised me was that the crappy switching power supply of the Raspberry Pi seemed to make no difference compared with my linear supply when the Singxer was used in the chain.

I suspect the Singxer does its job of isolating computer noise really well.

We are talking about really small details here, but my advice to you is simple: if you own an expensive audio setup and wish to get the best out of it, try out the Singxer SU-1.

For me, it’s the icing on the cake, and I don’t regret my purchase even one bit.

My money was better invested than in expensive cables that most likely do nothing to the sound.

But if you’re just starting out on your audiophile journey, I’d set my priorities elsewhere. Get the best headphones or speakers you can afford and then start to worry about USB interfaces.

A Hifiberry Digi+ is a pretty good choice already, and even external xCORE DDCs will come down in price.

One thing I wasn’t able to test was how well other music server setups respond to the Singxer in the audio chain. I’ll grab my Singxer and head to the next Head-Fi Meet. I will let you know how this turns out.

Pricing and Availability

When I originally reviewed it, the Singxer SU-1 sold for around $499. It has since been discontinued, so the original pricing and availability information in this article should now be considered historical.

Looking Back in 2026

I wrote this review in 2017, and I’ve deliberately kept my original listening impressions above. At the time, I felt that the Singxer SU-1 produced a small but repeatable improvement when feeding my Gustard X20u through I2S.

I would be more cautious about recommending a DDC as an automatic audio upgrade today. Modern DACs and streamers generally have much better digital interfaces than many products did a decade ago, and I certainly wouldn’t suggest spending several hundred Euros on a DDC before sorting out your headphones, loudspeakers and room.

That doesn’t change what I heard with the SU-1 in my system at the time. It simply puts the result into perspective. Even in the original review, I described the difference as subtle rather than transformative.

The Singxer also became part of a longer chain of experiments with digital playback. The SMSL M8, Gustard X20u and later the RME ADI-2 Pro FS R gradually changed how I think about digital source components and increasingly small upgrade differences.

For my current view on where DACs and digital front ends matter — and where they don’t — see Cheap DAC vs Expensive DAC and my current DAC Buyer’s Guide.

2026 note: The original article and subjective listening impressions have deliberately been preserved. I have only corrected language and grammar, updated internal links and added the short retrospective above.