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Drawmer HQ

Preamplifier & D‑A Converter
Published August 2011
By Hugh Robjohns

Drawmer HQ

Can a preamp and D‑A converter successfully straddle the pro-audio and hi‑fi markets? Drawmer believe it can...

British equipment manufacturers Drawmer will be very familiar to most people involved in pro audio, as they've established a long and impressive pedigree of analogue signal-processing and digital problem‑solving hardware, as well as a growing range of software plug‑ins. The latest addition to the company's portfolio is a rather unexpected one — not so much for its functionality, but rather its jaw‑dropping styling!

The HQ Precision Preamplifier/DAC is exactly that — a high‑quality stereo preamp with a built‑in D‑A Converter (DAC) — and is intended to function in the pro audio market as a monitor controller, as well as serving as a source preamp in high‑end hi‑fi systems. Other similarly specified professional and consumer hybrid preamp/controller products are on the market, but in Ivor Drawmer's own, inimitable, way the HQ does things differently, and a little more ingeniously!

Overview

First, though, I must comment on the styling of this unit. It's black. Very, very black, and very, very shiny too. It is an eye‑catching visual statement that looks every inch worth the not inconsiderable asking price. The mirror‑finished front panel is dominated by two huge rotary controls in the centre, with two smaller ones on the outside edges. The small ones are used to power the unit on and off, and to switch between two sets of line outputs (off, A, B, or A+B). The two large ones serve as the volume control and the input source selector. All four knobs are highlighted by an illuminated circumferential ring, in which a red‑tinted section indicates the current setting. The HQ is a very chunky product, too, weighing in at 6.6kg and filling a 2U rack space to a depth of 307mm. For the hi‑fi brigade, the rack ears are removable, while for the rackmounting professional, the feet can be removed.

The dual line‑outputs are configured such that output A is balanced and on XLRs, while output B is unbalanced and on RCA phono sockets. The balanced outputs provide up to +17dBu with the default factory gain settings, and the unbalanced outputs are nominally 6dB lower in level. However, internal jumper links allow the user to attenuate the output level independently for each output pair by up to 6dB (in 2dB steps). Additionally, either or both outputs can be switched (with more internal jumper links) to maintain a fixed output level, instead of following the volume control setting. It is also possible to boost the maximum output level up to +27dBu, if required, by using the input sensitivity options (see below) to increase the input levels.

The HQ boasts two standard quarter‑inch headphone outlets on the front panel, each driven from a dedicated buffer amplifier. The factory configuration enables the right‑hand headphone socket to mute both line outputs when headphones are plugged in, while the left‑hand socket doesn't. Yet more internal jumper links allow the user to choose whether or not either headphone socket mutes the line outputs.

The HQ 'family'. The HQ‑b has a blank front panel — which brings costs down — the idea being that you can do everything you need from your listening position, using the remote control.The HQ 'family'. The HQ‑b has a blank front panel — which brings costs down — the idea being that you can do everything you need from your listening position, using the remote control.The input selection is very comprehensive, with five digital and four analogue inputs to choose from. The analogue inputs comprise three on unbalanced RCA phono sockets, the third being switchable on the rear panel to accept an RIAA‑equalised low‑level input from one of those old‑fangled gramophone players (an earthing terminal is also provided). There's also one electronically balanced line input on XLRs. The digital side of things includes AES3 on both XLR and BNC sockets, S/PDIF on both RCA phono and Toslink optical inlets, and a USB input. Sadly, the last is restricted to 16‑bit signals at base sample rates, but at least it doesn't require any specific computer drivers — it is instantly recognised by both Mac OS and Windows. The other digital inputs can accommodate all of the standard formats up to 24‑bit, 192kHz. A buffered S/PDIF output of the last selected digital source (on an RCA phono socket) is also provided, and this can be used to feed an external digital recorder, meter system, or home‑theatre setup.

The nominal maximum output level from the HQ is achieved with 0dBFS on any of the digital inputs (of course!), and +8dBu on any of the analogue inputs — both balanced and unbalanced alike. The RIAA input requires ‑32dBu to deliver the maximum output level, but the sensitivity of each input can be adjusted up or down by 10dB courtesy of a rear panel 'set‑and‑forget' facility. Nine LEDs here indicate the currently selected input source, the sensitivity of which can be adjusted by pressing and holding one of three buttons (‑10dB, 0dB and +10dB). The new sensitivity setting is automatically stored internally and employed whenever that input is subsequently reselected.

Being able to adjust the relative levels of different inputs is very handy when trying to balance a number of disparate sources, however the 10dB steps are rather too crude for accurate professional monitoring applications. The Grace m904, for example — which is admittedly about 15 percent more expensive than the HQ in the UK, but includes full talkback facilities — provides the same ±10dB input sensitivity range, but can be adjusted in 0.5dB steps. That's the kind of resolution and flexibility that many users will feel necessary for accurate level matching between sources in a high‑end monitor controller.

Completing the rear‑panel facilities, power is connected via the usual IEC mains inlet (with integral fuse holder), and a removable metal cover-plate obscures the mains voltage selector switch that enables either 230 or 115V operation. Finally, two RJ45 sockets cater for an optional remote control (see the 'Remote Control' box) and allow multiple HQ units to be linked together for multichannel applications using standard Cat5e cables. When used with the optional HQ‑r remote controller all of the front‑panel controls (except the mains switch) are totally disabled and their illuminations are extinguished. To avoid the cost of redundant controls, Drawmer also offer a version of the HQ that has only the mains switch on the front panel (the HQ‑b).

Regarding multi‑channel operation, the Cat5e linking simply synchronises the source selection and volume settings between units: there is no facility here to decode multi-channel digital sources, for example, such as those encoded with Dolby Digital or DTS. The idea is that multi‑channel sources would be connected to multiple HQs and the outputs directed to the appropriate speakers.

Technology

The rear panel of the HQ features an array of analogue and digital I/O.The rear panel of the HQ features an array of analogue and digital I/O.

From a technology point of view, the HQ is an interesting device. A very thoroughly regulated linear power supply occupies the extreme right‑hand side of the unit, with two circuit boards filling the remaining floor area. The larger of the two is the main analogue board, with a pair of volume‑control sub‑boards mounted vertically, while the smaller PCB handles the digital inputs. Another vertical daughterboard runs along the front panel accommodating the controls and micro‑controller circuitry. As expected, construction is to a very high standard.

The USB input is handled by a Burr‑Brown PCM2704 interface, while the other digital sources feed a Cirrus Logic 8416 receiver. The output is passed to a Burr-Brown SRC4192 sample‑rate converter, which deals with source jitter, the output of which feeds a Wolfson WM8740 high‑performance DAC. The latter appears to be clocked from a 27MHz crystal, so the DAC probably runs at a fixed 210kHz or 105kHz sample rate for optimal conversion performance, the SRC resampling everything to suit. This approach is common these days, and has proven advantages.

The analogue side of the unit employs National LM4562 ultra‑low distortion op‑amps, with sealed relays everywhere to switch between sources and activate other functions. The volume control circuitry is divided into left and right sections on individual daughterboards, each carrying nine sealed relays, which apparently control the volume in 0.5dB steps. A THAT 2180 Blackmer VCA chip is also fitted on each board, and this is where Drawmer's innovation comes in!

While the relay‑switched resistor‑attenuator volume control is widely recognised as the most accurate and transparent methodology, it also tends to be rather noisy when the level is being adjusted and all the relays chatter. Drawmer's unique solution, called SRVC, or 'Seamless Relay Volume Control', is to switch instantaneously across to the VCA as the volume control knob is moved. This allows the volume to be tweaked without the distraction of distant machine‑gun fire and then, in the instant that the knob is released, the required relays are apparently engaged again, so that the user hears only one click. It's a very neat solution and typical of Drawmer's lateral thinking to solve a common problem!

Intriguingly, though, I found that I was actually able to adjust the volume continuously to trim the output level precisely, just as you would expect from a conventional analogue volume potentiometer. The distinctly 'quantised' level steps that conventional relay‑based systems normally impose seemed to be absent. It's no surprise that the VCA element is active when making fine control adjustments, but I was expecting to see the level then jump to the closest available resistor‑chain setting after the control was released — and there was no obvious sign of that. So I'm not sure how the volume system is controlled... but it's very clever!

The SRVC technology has also enabled Drawmer to incorporate some nice 'safety' features intended to avoid unexpected loud noises, such as when the unit is powered up or when the line output selection is changed. For example, if the volume knob is below halfway when the unit is first powered on, the output fades up gracefully. If it's over halfway, the outputs remain muted until the knob is turned down and back up again. Similarly, if the line outputs are muted (perhaps because headphones are plugged in, or the output selector has muted one or both channels), unplugging the phones or changing the output selection causes the volume to fade up gracefully again. It's all done in a very elegant and thoughtful way.

Listening

The published specifications for the HQ make impressive reading, and my own bench tests using an Audio Precision x515 analyser confirmed most of them. Inter‑channel crosstalk was well below ‑100dB, while the Total Harmonic Distortion plus Noise (THD+N) figure was better than 100dB relative to the normal peak output level. The claimed channel matching of better than 0.1dB at any volume setting was also met, and frequency response was well within the specified ±0.1dB tolerance from 20Hz to 20kHz. In fact, I measured ‑0.5dB points at 7Hz and 80kHz for the balanced analogue inputs. However, my test figure for the DAC's dynamic range, using the standard AES17 protocol, gave a figure of 104.5dB, which is lower than the unweighted 113dBFS figure Drawmer claim. For comparison, my reference DACs — a Grace m902B and Benchmark DAC1 — managed AES17 figures of 108.8dB and 113.4dB, respectively.

Critical listening tests quickly confirmed the HQ's high‑quality signal path, with superb stereo imaging and depth, and very smooth and quiet backgrounds. I was unable to hear any significant quality change when adjusting the volume control (and therefore switching between relay and VCA‑based attenuators), and I couldn't measure any reliable difference either. However, I felt there was a hint more 'colour' involved in the HQ's sound character than was evident in either the Grace or Benchmark DACs. The HQ has a subtle but identifiable mid‑range richness not evident in either of the other reference units. For overall sound quality, though, I can't fault the HQ, which is a very natural and musical preamp to audition, with a detailed and revealing character that never becomes over‑etched or fatiguing in the way some lesser monitor controllers can. The large source selector and volume controls feel nice and solid in use, and the whole preamp exudes an air of excellence.

Verdict

The HQ is a very high-quality product, and the SRVC technology is extremely clever — I hope it will find applications in future Drawmer products. But if I have to be picky (which I do; it's my job!), the absence of dim and mono facilities marks the standard HQ down significantly as a professional monitor controller. Although both functions are provided on the optional HQ‑r remote (see box, left), I feel the HQ is much more appropriate for high‑end hi‑fi applications than as a professional monitor controller. The absence of talkback facilities and cue feeds also restrict its applications and, more importantly, renders it expensive compared to similarly equipped competition.

That said, the blank‑panel HQ‑b version with the HQ‑r remote controller is a far more practical prospect, albeit still a rather expensive one. Indeed, the HQ‑r is an elegant controller in its own right, and clearly designed with the professional user in mind.  

Alternatives

The new Grace m903 is 25 percent less expensive in the UK than the HQ, but provides an almost identical function set and technical performance, while the Grace m904 is 15 percent more expensive, but offers considerably more features and facilities, making it a far more comprehensive monitor controller. The Dangerous STSR system is also a strong contender, with a relay‑based volume control system, and although it has no digital inputs, it does have cue and talkback facilities, and a very cost‑effective upgrade route for surround applications.

Remote Control

The HQ‑r remote‑control unit is a very compact and neat desktop unit, with a large central volume knob accompanied by arrays of buttons on each side and below. The unit measures a modest 250x82x88mm (WxHxD) with a nicely angled front panel, and there is provision to secure the controller via base or side screw fixings, if required. It connects to the Remote In socket of the HQ unit using a standard Cat5e cable (supplied), and if multiple HQ's are to be linked for multichannel applications, short Cat5e cables are required to link the Thru output socket of the first HQ to the Remote In socket of the next, in a daisy‑chain fashion. The HQ‑r controller is powered via the cable.

To the right of the volume knob, nine illuminated buttons select and indicate the current source, while to the left, the top row of buttons activates the line outputs. The second row of buttons accesses two preset volume settings or enables the volume controller knob. The two preset volumes are established via multi‑turn trimmers on the HQ‑r's rear panel. A three‑digit LED display completes the facilities on the left hand side, indicating the current volume with 0.5dB resolution. Arranged in an arc below the volume control, three more buttons provide dim, mute and mono functions.

The dim button reduces the volume by a fixed 30dB, while the mute button attenuates the output to around ‑91dBu. Strangely, this is not as good as disabling the output with the speaker selector, which renders a noise floor of ‑108dBu. If course, this discrepancy is of no practical significance, but it does indicate that the mute function is not performed by using the output relays... which my inner geek finds intriguing!

Published August 2011

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