NuForce DDA-100 Integrated Amplifier

Insomniacs must populate NuForce’s R&D department. That’s the only explanation I can come up with for NuForce’s rapidly expanding stable of new products. I reviewed its excellent DAC-100 in Issue 228, and now NuForce has introduced an even more revolutionary digital product—a direct- digital integrated amplifier that utilizes pulse-width-modulation technology.

Priced at a paltry $549 the DDA-100 delivers value with a capital V. You get four digital inputs (no analog—remember, this is an all-digital amplifier), one TosLink digital output, and one pair of speaker terminals. NuForce even throws in a nice little credit-card remote control. Add a computer to the front end and a pair of speakers on the back and you’ve got a completely modern audio system. And, I will brashly add, the DDA-100 sounds better than any conventional integrated amplifier I’ve heard priced under $2500.

Technical Tour

According to NuForce, “The DDA-100 doesn’t require the typical DAC stage found in most of today’s digital audio products. Rather, its PWM power amplifier stage is modulated directly by the incoming signal, and the digital-to-analog conversion takes place at the speaker outputs. In effect, the PWM power amplifier stage operates as a power DAC.” The DDA-100 supports any 16- or 24-bit digital signal, from 44.1 to 176.4 (but not 192 kHz) via its one S/PDIF input. The two TosLink and single USB 2.0 inputs support up to 96kHz and 24 bits.

For a description of how PWM power amplifiers work, please read Robert Harley’s sidebar. Suffice it to say that PWM is not the same as switching amplifiers, such as Class D or T designs, and offers the technical advantages of a simple signal path and fewer active components, as well as a few ergonomic drawbacks.

Setup and Ergonomics

The DDA-100 principal market is audiophiles who want a simple, moderately priced, one-box solution to go from any conventional digital source directly to a pair of loudspeakers. Headphone and subwoofer users will need to add additional components to the signal chain. Using either a USB to S/PDIF converter box with multiple digital outputs (one for the DDA-100 and a second one for your headphone DAC) or a USB DAC with an auxiliary S/ PDIF output, will expand a DDA-100-based system’s capabilities to handle more ambitious systems.

Hooking up the DDA-100 is easy as long as you keep it simple. If you do any amount of headphone listening you’ll need to add another DAC to your system, since the DDA-100 has no headphone output. For headphones I used the NuForce DAC-100—I gave it the TosLink output from the DDA- 100. Using the DAC-100 also supplied me with a line-level subwoofer feed if I needed one. Another option I looked at was NuForce’s new headphone amplifier, the HAP-100, but it only has analog inputs. You will need a headphone amp that has a DAC and a TosLink input to interface with the DDA-100.

At 50W RMS (8 ohms) the DDA- 100 is far better suited for speakers, even desktop speakers, that are at least 88dB sensitive. With some of my less sensitive monitors, such as the Aerial Acoustics 5B’s (86dB), I could hear the amplifier section beginning to strain during dynamic peaks. And because the DDA-100 is such a low-noise device (true 95dB S/N from digital input to analog power output) variations from its optimal operating range were readily apparent.

For computer sources NuForce supplies a basic USB interface that supports up to 96/24. For higher resolutions you must use either the RCA S/PDIF input or TosLink. Unfortunately for us high-resolution addicts, 176.4/24 is the maximum resolution supported by the DDA-100. If you try playing full-resolution 192/24 files through the DDA-100 all you will hear is modulated noise through your speakers.

Sound

The DDA-100 was my first encounter with a PWM amplifier, and I was impressed by its lack of coloration and the absence of electronic noise. In my desktop system, regardless of what speakers the DDA-100 was tethered to, it always produced a more convincing soundstage than I’ve experienced before. Locational cues were simply easier to decipher, as was all sonic information.

During the initial stages of my review I used the DDA-100’s USB input, and while it didn’t sound bad, the USB input is certainly not the DDA-100’s “best” input. Through the USB the sound had a slight but pervasive opaqueness when compared to better, lower-jitter sources coming from the S/PDIF input. I used several outboard USB/SPDIF converters with the DDA- 100, and in every case the inclusion of a dedicated outboard USB converter in the signal chain rewarded me with a better and more transparent sound.

Since this is a review of the DDA-100, not USB converters, I will not go into great detail enumerating differences between various USB boxes through the DDA-100, but I will tell you that the DDA-100 offers sufficient resolution to easily hear that a Bel Canto RefLink or Empirical Audio Off-Ramp 5 delivered better low-level detail and resolution than a $60 Matrix converter.

But how does the DDA-100 sound different than more conventional amplifier designs? During listening sessions I was continually aware of the DDA-100’s lack of haze and homogenization in the “black space” between instruments. The edges and dimensions of each instrument were defined in a more concrete manner through the DDA-100 than any amplifier I’ve heard near its price. On my recently recorded “field recordings” of Chris Thile, Chris Eldritch, and Gabe Witcher from a Rockygrass Academy workshop on improvisation, not only did the DDA-100 place each musician in a cohesive and dimensionally convincing soundstage, it also allowed me to hear into the background so well that I could clearly identify Pete Rowan’s vocals coming from another tent 75+ feet away.

As for any traces of a “characteristic” sonic signature in the DDA-100, I have yet to hear one. Unless driven into clipping, I could not identify any additive colorations that I could attribute to the DDA-100. As for subtractive colorations, compared to a traditional tube design, the DDA-100 will not be as warm or harmonically rich in the lower midrange, but I wouldn’t call this a subtractive coloration as much as a lack of an additive one. The bottom line was that for me, with current sources, the DDA-100 was sufficiently transparent and uncolored to be used as a reference device as long as it was mated with sufficiently sensitive and unproblematic transducers.

Final Thoughts

You can view the NuForce DDA-100 in two ways—it’s either a supremely high- value entry-level integrated amplifier or it’s a component that lacks just a few vital features needed to make it into a devastating price- no-obstacle-to-performance component.

The issues with the DDA-100 are primarily ergonomic. It can play 176.4/24, but lacks the ability to play 192/24 files. Through USB it can support only up to 96/24, but will handle up to 176.4 through S/PDIF. It also has no analog outputs for headphones or subwoofers, and is only 50W RMS (into 8 ohms). And while you can remedy the paucity of analog outputs by linking the DDA-100’s sole digital output (which is TosLink) to a second DAC with headphone and analog line-level outputs, this adds substantially to the complexity and cost of a system.

But the sound of the NuForce DDA-100 is so impeccable, up to the point when it runs out of power, that even after adding a NuForce DAC-100 to augment the ergonomic flexibility of the system, the final cost is still a sonic bargain. I haven’t heard any integrated amplifier with DAC capabilities priced near this combo that offers any serious sonic competition.

If you have sensitive speakers, at least 88dB, and can work around the DDA-100’s ergonomic limitations, you may find that the DDA-100 is simply the best integrated amplifier solution that you’ve ever heard. And for those readers who still firmly believe that all-digital amplifiers are for someone else’s system, listening to the DDA-100 will be, as it was for me, a revelation.

SPECS & PRICING

Digital input: Two TosLink, RCA coaxial 75-ohm, USB 2.0 adaptive mode
Sampling rates: USB: 44.1, 48, and 96kHz; S/PDIF: 44.1, 48, 88.2, 96, 176.4kHz
Resolution: 16–24-bits
Power: 75W (4 ohms), 50W (8 ohms)
Frequency response: 20 to 20kHz +/- 0.1db SNR > 95dB A-weighted
Dimensions: 9″ x 2″x 8.5″
Weight: 2.64 lbs.
Price: $549

NUFORCE, INC.

382 South Abbott Ave.
Milpitas, CA 95035
(408) 890-6840
nuforce.com