Swissonic AD24 and DA24 Converters

PLEASE NOTE: This article has been archived. It first appeared on ProRec.com in July 2000, contributed by then Senior Editor Gary Simmons. We will not be making any updates to the article. Please visit the home page for our latest content. Thank you!

Although the Swissonic name is relatively new (they were formerly known as MusicNet), the AD24 and DA24 are no strangers to the US pro audio market. These highly regarded converters have been available from Sonorus as the AudI/O AD/24 and DA/24. Sonorus was simply re-badging the Swissonic units (i.e. same box, different paint).

Now, Swissonic is bringing their products directly to you. These converters, as well as the entire Swissonic product line, are now being distributed by Swissonic America. Sonorus is also offering the entire product line, although they will have the Swissonic name on them. The rapidly expanding Swissonic product line also includes a USB audio interface (the USB Studio D) as well as other converter options (see ProRec review of the AD96 and DA96).

The AD24 ($749 list) and DA24 ($599 list) are 8-channel A/D and D/A converters featuring balanced analog I/O and the industry standard ADAT Lightpipe interface for the digital connection. The Lightpipe interface allows you to use the converters with a wide variety of digital mixers and soundcards. I wanted a high quality set of A/D converters to feed my soundcards (Yamaha DSP Factory and Creamware Pulsar), and had read nothing but raves from end-users, so I bought one of each as soon as the Swissonic units hit the US.

The AD24 and DA24 are half rack units. I personally like the half-rack approach since it lets you buy the combination of converters you need. I had a spare rack shelf, so I didn’t purchase the optional rack shelf. I probably should have purchased the shelf too, as the holes in my “universal” shelf didn’t line up perfectly. Let’s take a look at the hardware, starting with the AD24.

The front panel of the AD24 features eight pairs of signal level LEDs, three buttons (with status LEDs) and the power switch. The signal level LEDs indicate signal present (green) and a clipping warning (red). There are buttons to select the sample rate (44.1K or 48K), the clock source (Internal or External) and a Calibrate button.

The AD24 manual recommends that you calibrate the AD24 (for best performance) each time the unit is powered on, or when the clock settings are changed. Calibration is easy. Just push the Calibrate button and wait a few seconds for the LED to turn off.

The rear panel of the AD24 contains eight analog inputs (XLR, +4dBu, balanced), the Lightpipe output, word clock input (on BNC) and the power connection. The AD24 is powered by a “lump in the line” style transformer.

The front panel of the DA24 looks identical to the AD24, but the buttons perform different tasks. The three buttons on the DA24 let you select Deemphasis (on or off), the sample rate (44.1K or 48K) and the resolution (16 bit or 24 bit).

The rear panel of the DA24 also looks similar to the AD24. It features 8 analog outputs (XLR, +4dBu, balanced), the Lightpipe input, word clock output (extracted from the Lightpipe input) and the power connector. The DA24 is powered by a “lump in the line” style transformer.

Installation

I’m going to go off on an installation-related tangent since most of us live in the messy world of project studios that contain a wild mix of balanced and unbalanced connections at varying signal levels on all manner of connectors.

Here’s my Cliff Notes version of interfacing gear in the studio:

Balanced wiring uses three wires. Unbalanced uses two. Balanced does a better job of rejecting noise, but unbalanced is probably fine for line level (or hotter) signals if you use good quality cable, keep the cables short and avoid running the cables next to noise sources like power strips and wall warts (power transformers).

Balanced wiring usually uses XLR or TRS (stereo ¼” phone plugs) connectors. Unbalanced wiring usually uses RCA or TS (mono ¼” phone plugs) although some consumer soundcards will use an 1/8″ mini-jack for line level signals.

Analog signal levels come in three major flavors: mic, line and speaker. Mic level signals are usually pretty low (voltage wise), although some condenser mics have a very hot output (approaching line level). That’s why you need a mic preamp to amplify the signal. Line level is what most rack gear uses for ins and outs. Speaker level is the output of a power amp for feeding speakers. Low-level signals are affected more by noise than high-level signals, which is why mic cabling is almost always balanced.

There are two flavors of line level signals, commonly known as –10 and +4. The “-10” name is shorthand for “-10dBV” which means 10dB below a reference voltage of 1 volt. “+4” is shorthand for “+4dBu” which means 4dB above a reference voltage of 0.775 volts. In the real world, a nominal “-10” signal is 316 millivolts. A nominal “+4” signal is 1.23 volts.

Since the two levels use different reference voltages, the actual difference between them is 11.8 dB, not 14 dB. See Lionel Dumond’s articles in ProRec that explain all you’d ever want to know about signal levels if you want more info…

The last thing we need to think about is headroom. This is a trickier issue in the world of A/D and D/A converters since there is no “standard” that everyone agrees on. Most soundcard makers publish specs on how their converters work. The things to look for are what signal level does an A/D converter need to produce a full-scale digital signal (0 dBFS). Likewise, look for info on what signal level is output by the D/A converter when presented with a full-scale digital output.

We need to be sure our analog input is hot enough to drive the A/D converter to 0 dBFS. If it isn’t, you’ll be wasting bits which adds quantization noise to your recordings. We also need to be sure that our mixer or powered monitors can handle the analog output of the D/A converter without distortion or clipping.

So what does all this have to do with the Swissonic converters in question? The AD24 and DA24 are definitely targeted at “pro” users. The analog ins and outs are balanced +4 dBu on XLRs. It takes a +20dBu signal to drive the AD24 full-scale. Likewise, the DA24 will produce a +20 dBu output on a full-scale digital input. If you do the math, you’ll see that nominal analog signal levels (+4 dBu) equal a –16 dBFS digital signal.

It would have been more flexible if Swissonic had used TRS jacks that could deal with balanced and unbalanced cabling along with switchable -10/+4 signal levels. So I asked why they only offered balanced, +4 I/O on XLRs… I was told that in order to get the very best performance out the units, they had to pick an I/O standard and optimize the design appropriately. I’m no EE, but I’ve been told similar things by engineers at other soundcard companies. Makes sense to me…

So, if your studio uses +4 dBu, balanced wiring on XLRs, then hooking up the AD24 and DA24 is painless. Just plug them in and go.

My good mic preamps (Earthworks LAB102 and Daking 52270s) have balanced, +4 dBu outputs on XLRs. Hooking them up to the AD24 was simple. A handful of short (3′) mic cables did the trick. The Sub outputs (and direct outs) on my Mackie 1604-VLZ mixer are balanced TRS (with a nominal level of 0dBu) and are capable of putting out +22dBu. So I hacked the female ends off four 10′ mic cables and replaced them with TRS connectors. No big deal so far…

As I mentioned earlier, the AD24 will output a full-scale digital signal (0 dBFS) if you feed it a +20dBu signal (16dB above the nominal, +4dBu level). Some semi-pro gear can’t put out a signal that hot. This means that if you don’t find a way to bump the input signal up, you won’t be using all the bits the converters can put out. Luckily, each channel of the AD24 can add about 10dB of gain to the signal if you remove an internal jumper. So I opened up the AD24 (2 screws on each side and 16 on the back) and checked out the jumper situation. It’s no big deal to remove the jumpers (save them!). You’ll spend way more time messing with the 20 screws holding the top on than removing the jumpers… Since my gear was capable of feeding the AD24 a hot signal, I left all the jumpers in, but it’s nice to know that Swissonic planned ahead for people using –10 dBV gear.

There were similar issues with the DA24. Yes, I could have just hooked the first two DA24 outputs directly to my powered monitors, but I prefer having a volume control between my soundcard and my powered monitors. So I made an XLR-to-TRS cable to feed the DA24 output to the aux return inputs on my Mackie mixer and used the volume control on the mixer to control the level in the studio.

Unlike the AD24, the DA24 does not have any internal jumpers to adjust the gain. It will always output a +20dBu signal with a full-scale input. That hot a signal will possibly overdrive your standard -10dBV semi-pro input. The inputs on my Mackie 1604-VLZ list a maximum input level of +22dBu, so I had a couple dB of room to spare there. Be warned. If this is a problem for you, the Swissonic manual shows how to make cables with built-in attenuators (as well as bunch of other interface cables).

So, when it was all said and done, I spent a few hours with a soldering iron hacking up mic cables and putting different ends on them. Yes, it was a pain in the ass, but it wasn’t the end of the world either, and you only have to do it once…

Listening

I know, I know… Cut to the chase. What do they sound like? Pretty damn nice if you ask me.

I used the AD24 for a few months while finishing overdubs (vocals, percussion, acoustic and electric guitars) on a solo album project for an old bandmate. My Earthworks LAB102 mic preamp provides multiple outputs, so it was relatively easy to record two versions of a given track; one through the AD24 and one through the converters on the DSP Factory. When I A/B’d the tracks, the AD24 tracks sounded more open and real. I don’t claim to have golden ears, but I heard a distinct improvement, so I considered the AD24 to be money well spent.

I spent a little less time with the DA24 because I was basically too lazy to make the required cabling to hook it up to my mixer. Big mistake. When I finally got the DA24 hooked up, playback of tracks I’d been working on for months were now clearer and more detailed. The thing that struck me was being able to really hear the reverb tails.

What I really wanted to do was A/B/C the Swissonic units with the Frontier Designs Tango24 (somewhat less expensive) and something more pricey, like the Apogee AD-8000. Unfortunately, I was unable to track down either piece of gear for a head to head test.

Summary

I’m a practical guy. I tend to spend my money on mics, and my time finding the right mic (and position) for the source I’m recording. The sonic differences between converters are more subtle than the sonic differences between mics. However, once you’ve found the right mic, the right position and the right preamp, you want to capture the best possible digital representation of the signal that you can. Everything matters.

I don’t spend money on gear to be fashionable. I don’t buy into hype or voodoo. If a piece of gear doesn’t sound better than what I’ve already got, it goes back. The Swissonic AD24 and DA24 are keepers. They sound great and are affordable. No, they’re not the cheapest converters on the block, but they’re nowhere near the most expensive either. I think they offer a great bang for the buck. Check them out.

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