NAD 118 digital preamplifier
By Kalman Rubinson   •   July, 1998 Tone controls? I ripped them out of my Dyna PAS-3! And that was the last time I had tone controls. As a card-carrying audiophile, I wanted just what the engineer had inscribed on the recording, with as little change as possible (read: high fidelity).

But such purism has left me unarmed against boomy or screechy recordings of wonderful music. The only choices have been to endure or abjure such recordings because analog frequency shapers (tone controls, equalizers, filters, etc.) add phase-shifts, noise, and distortion. At the same time, mid-fi and home-theater systems (and recording studios) incorporate sophisticated and complex frequency-shaping, modifying tonal, decay, and reverberation characteristics with digital signal processing (DSP) to superimpose a chosen aural ambience on the sound source. Few of us on the other side of the track, who have taken the more ascetic route, would deny that these effects can be impressive,

Now, the time has come for DSP to give the audiophile some powerful tools to tailor frequency response and to correct faults in the recording. Both the Z-Systems rdp-1 and the NAD 118 are designed to use digital signal processing to effect changes in the shape of the frequency response without introducing any side effects into the audible signal. Both products rely on powerful general-purpose DSP chips, have memory modes for the storage and recovery of settings, and can be operated from their front panels or from their remote controls.

Aside from those common points, they differ in terms of capabilities, intended applications, and user interface because the designers of these two devices chose different models to emulate. The NAD emulates a line-level preamp/controller with tone and separation/blend controls. The Z-systems rdp-1 emulates a controller/parametric equalizer. Each, however, is much more capable than its ancestors.

Meet the NAD 118
Although it handles analog as well as digital signals, NAD calls the 118 a "digital preamp." Since the signal processing operates in the digital domain (using a 24-bit Motorola 56004 DSP chip), analog inputs are converted to digital by a Philips SAA7360 18-bit, 48kHz-sampling ADC; analog outputs are driven by the Philips 20-bit TDA1547 DAC used with a TDA1307 digital filter. The ADC's 48kHz default sampling frequency can be changed to 44.1kHz if necessary. TDA1315 S/PDIF I/O chips handle digital inputs and outputs. (A separate TDA1305 DAC is dedicated to the tape-monitor loop.) All of these are among Philips' best offerings in their respective applications, and are found in other high-end components.

You needn't concern yourself with any of this, as the basic operation of the 118 will be intuitive to anyone who has used other audio gear. Take it out of the box and you can hook it up to your system just as you would any other preamp. Plug your analog sources into the analog inputs and your digital sources into the digital inputs. Connect your power amp to the outputs and you're ready to go. (What do you do with your DAC? Keep it handy.)

With notable exceptions, every control on the front panel and remote does what you'd expect, and tiny LEDs clearly indicate the status of each control. But there's much more lurking behind NAD's conservative front panel. Input sensitivities should be adjusted individually for each analog source. Of course, it's nice not to get blasted when changing from a lower-signal-level input to a higher one, but, since the 118 digitizes the analog inputs, it's essential that the input gain be set to match the dynamic range of the ADC. Using a dynamic and fairly loud source, input sensitivity is set by holding down the input selector button and turning the volume control until the overload LED flashes only briefly and infrequently. Once adjusted, the 118 remembers the setting for that input. You can also set the analog output level to "High" or "Normal" to match the input sensitivity of your power amp(s).