Digital Processor Reviews

As I wrote in my review of the Bricasti M1 D/A processor in February 2012, it seemed a good idea in the late 1980s: upgrade the performance of your CD player by feeding its digital output to an outboard digital/analog processor. British manufacturer Arcam, one of the first companies to see the opportunities in this strategy, introduced their Black Box in 1988. When I reviewed the Black Box in February 1989, I found that its low-level linearity was among the best I had measured at that time for a product featuring the 16-bit Philips TDA1541 DAC chip set. However, that linearity still wasn't very good in absolute terms. Back then, it required heroic and expensive engineering to obtain D/A performance that did justice to the 16-bit CD. These days, however, the semiconductor foundries produce a plethora of relatively inexpensive D/A processor chips that both handle 16-bit data with ease and wrest full resolution from 24-bit data.

In 1989, the original Arcam Black Box with coaxial and TosLink S/PDIF inputs cost $798, which, taking inflation into account, was equivalent to $1494 in 2011. In 2012, Arcam introduced a successor, the FMJ D33, that still comes with coaxial and TosLink S/PDIF inputs, but now includes an AES/EBU input, two USB ports, and a Type A port for iDevices. The 1980s Arcam processor was limited to sample rates of 48kHz and below, and was stuck with the 4x-oversampling digital filter that came with the Philips chipset. The FMJ D33 handles data with sample rates up to 192kHz and offers the choice of three digital filters. This all comes at a price: a penny less than $3200. Wanting to see how much had improved in the 24 years since I auditioned the Black Box, I asked for a review sample.

Full metal jacket
Like the progenitor of the line, the FMJ D33 is a plain black box. A U-shaped chassis, formed from nonresonant steel and supported on four compliant feet, is complemented with an aluminum cover and front panel. An array of six LEDS on the left of the front panel indicates the sample rate (44.1, 48, 88.2, 96, 176.4, and 192kHz), and a row of seven pushbuttons selects the digital input. An LED above each button glows red if no data are present when it's pushed, and green when valid data are detected. An eighth button, marked Filter, selects one of the Arcam's two custom digital anti-imaging filters, each indicated with a green LED. When neither filter is selected, both LEDs remain dark and the D33 reverts to the Burr-Brown DAC chip's default 8x-oversampling filter. A ninth pushbutton acts as the Power switch. All buttons are duplicated on the remote control, which also boasts volume up/down buttons and transport controls intended for use with Arcam's integrated amplifiers and CD players.

The rear panel offers, from left to right: a two-pronged IEC AC receptacle; AC voltage selector; an RS232 port to allow remote control from custom-installation setups; a 12V trigger and remote input jacks; the digital inputs (two TosLink S/PDIF, two coaxial S/PDIF, AES/EBU, and three USB); and the analog outputs, comprising one pair of balanced XLR jacks and two pairs of unbalanced RCAs. As well as a USB port for iPods and iPads, etc., there are two USB ports, one marked Class 1 Isolated for USB1.1 devices, the other Class II High Speed, for those that can operate in USB2.0. No driver program is required for the latter with Apple computers; Arcam provides, on CD-ROM, a driver for use with Windows machines. A slide switch selects which of the two USB inputs is active.

Inside, the digital and analog circuits are carried on a large, four-layer circuit board running the full width of the chassis. Two toroidal transformers supply independent power to the digital and analog sections, the latter having smoothing capacitors and heatsunk voltage regulators close to the active circuitry.

The AES/EBU and S/PDIF inputs feed an AKM AK4113 receiver chip, the AES/EBU being isolated with a pulse transformer. The USB inputs, both operating in asynchronous mode, are handled either by an Analog Devices ADUM3150 transformer-isolated receiver chip (USB1.1) or an XMOS chip (USB2.0). It looks as if the datastream from the selected digital input is dejittered with a TCD2210 chip from TC Technologies before being sent to the digital filters, these realized in a Xilinx Field-Programmable Gate Array (FPGA), then sent on to the D/A section.

One DAC chip is used per channel, this the high-performance PCM1792 from Burr-Brown, which can operate with 24-bit precision at sample rates up to 192kHz. This chip is popular in the High End, being found in the PrimaLuna ProLogue Eight and Vincent Audio C-60 CD players, the Ayre Acoustics C-5xe^MP universal player, and the Bel Canto Design e.One DAC3.5VB and Musical Fidelity V-DAC II D/A converters, as well as the ASUS Xonar Essence ST and STX soundcards. Though the PCM1792 is a two-channel device, it can be used in bridged-mono mode to maximize resolution. Each PCM1792 feeds a pair of National LME49722 high-speed, low-noise, dual–op-amp chips, which are followed by a low-noise National LME49990 op-amp, apparently to sum their outputs. The balanced outputs use Burr-Brown DRV135 balanced line-driver chips; the single-ended outputs use LME49722 chips.

In an age when some manufacturers endeavor to keep their products' country of manufacture a secret (and complain when we out those secrets in our reviews), the FMJ D33's rear panel proclaims that it is "Designed and Manufactured in the UK."

Sound quality
Setting up the FMJ D33 was no more complicated than feeding its high-speed USB input the datastream from my Mac mini and selecting "ARCAM USB Audio 2.0" in Pure Music's Audio Setup menu. I used the Arcam's balanced outputs exclusively for my auditioning.

Because the D33's iDevice input will work only with products that allow a digital output—iPhone 4, 4S, iPod Touch 4G, iPads 1 and 2—it was not compatible with my iPod Classic 160GB or iPhone 3GS. As I report in the "Measurements" sidebar, the Arcam's AES/EBU input would not lock to the Audio Precision SYS2722's AES/EBU output. However, it did successfully lock to the AES/EBU output of my Ayre QA-9 A/D converter at all sample rates up to 96kHz, though not higher. The USB2.0 input had no problem playing files recorded with 176.4 or 192kHz sample rates. Ray Brown's classic Soular Energy album (24-bit/192kHz Apple Lossless files ripped from DVD-A, HiRez Music HRM2011), for example, was reproduced with a rich, purring tone to Brown's double bass, and grain-free treble in the cymbals and piano.