I was looking for a DAC to complete my new stereo system. I use an Apple MacBook with Decibel to play digital music via the DAC. The rest of the system consists of DIY preamplifier (Thel VX-D, battery powered class-A MosFet output), two Hifiakadmie PowerAmps, and AOS Studio 24 BE speakers (top-of-the-line ScanSpeak drivers).

Some more specific requirements for my new the DAC were:

• High-Res (192/24) asynchronoous USB or FireWire input
  
• Discrete analog stage would be nice
  
• No volume control or other gimmicks required
  
• Down-to-earth price! It's just very wrong to pay $5000 for a $15 DAC chip, a bunch of $0.05 opamps and a $2.50 «audiophile» face plate made of the same material as kitchen aluminium foil. I really don't want to support this sick part of the audio industry.
  

I looked at many different DAC offerings, and I found a very nice list of different DACs with asynchronous USB and FireWire inputs. One of the least flashy DACs on this list was the new Linnenberg UDC1, which seemed like a perfect fit to my requirements. Also, Udo Linnenberg of Linnenberg Audio claims that he's not making a living from his audio «business», so maybe the price-to-value ratio of the UDC1 is better than with other DACs.

I gave the UDC1 a shot in in December 2011, when price was hot. Udo Linnenberg also offered a full return if I don't like the UDC1, so I couldn't really go wrong. The UDC1 has a built-in M2-Tech USB interface, which accepts up to 192kHz/24Bit (or 32Bit, I'm not sure). The USB interface has its own dedicated power supply, so it doesn't rely on the noisy USB power from the computer. The DAC chip is a good old Burr Brown PCM1794A, which drives a discreete analog stage. The analog signal is output to symmetric XLR jacks only, so there are no RCA. I therefore had to use XLR-to-RCA adapters to use the UDC1 in my system. No big deal, but RCA jacks would've been nice. The power supply is completely built into the box. The lack of a wall wart is nice because I hate wall warts cluttering up the power outlets. But I also like wall warts because they can be replaced by something better (e.g. a DIY power supply), which is often a very easy tweak to considerably improve the performance of audio electronics.

The USB interface built into the UDC1 requires a special driver software, even for current Macs. This is a little unusual, and I am a bit afraid of what's going to happen if the drivers stops working with a newer version of Mac OS X and M2-Tech stops supporting the software for the UDC1. It also means that it might be difficult to make the UDC1 work with Linux, because there is (currently) no Linux driver available (shame on M2-Tech!).

Another slight annoyance is the power indicator LED, which is waaaay too bright. The UCD1 could almost light our entire living room with its uncomfortably bright blue LED! Udo Linnenberg instructed me how to reduce the LED brightness by replacing a resistor. I'd be comfortable doing this, as I know where to hold a soldering iron. Others might not. I solved the bright LED issue simply by stuffing the UDC1 away behind my audio rack, somewhere in the middle between the computer and the preamplifier.

So, how does it sound? I compared the UDC1 to my Apogee Mini FireWire DAC (hot rodded with a hefty DIY power supply, which replaces the original wall wart) in my system as described above. With the UDC1, the sound was more detached from the speakers. The sound was «juicier» and livelier, whereas the Apogee sounded dryer and calmer. The bass was better resolved with the UDC1 and there was more air in between the instruments and vocals. I'd say the overall score of my digital chain with the UDC1 is about the same as the vinyl chain (although they certainly don't sound the same). Really good!

Although I was not able to compare the UDC1 to the usual $5000+ «reference» DACs with $0.05 opamps behind the face plate, I am pretty sure the sound quality is up there. I therefore don't know if the UDC1 is a giant killer, but it might well be…

But can UCD1 be improved? Yes. First of all, the LED brightness needs to be reduced, it's just ridiculously bright. And then I am a big believer in clean supply power. That's why I use battery power in my phono and line preamps, and an elaborate outboard power supply with a large C-L-C filter for the Apogee Mini Firewire DAC instead of the cheap wall wart. However, doing this with the UDC1 is not trivial, because the power supply is built into the box and sits on the mainboard. And, although the USB interface works very well, I'd really appreciate the freedom to be able to use it without a proprietary driver that might stop working in the future or does not exist for some operating systems.