Outboard-Gear

dbx 676 Channel Strip and PAU 805 4-Channel Preamp

Two Solid Front Ends for Getting Audio Into Your DAW

If there’s no console in your recording workspace, there are two ways to go when purchasing preamps. One option is to buy the cleanest no-frills preamp possible, to which you can add processing, if needed, via plug-ins or separate hardware. But sometimes you need a full-featured channel strip with EQ, compression/limiting, and even a digital back end offering an all-in and portable solution for vocal and other recording. The two products reviewed here take these different approaches. The dbx 676 is a full-featured mono tube channel strip, while the PAU Audio 805 offers four channels of high-end preamplification.

dbx 676 Channel Strip

The 676 is housed in a double-rackspace enclosure that contains a tube-driven mic preamp, equalizer, compressor and limiter. The preamp is designed with great flexibility in mind, starting with the power supply and its 250-volt rail. High-voltage powering is a technique typically used in preamps that aim for the cleanest signal with the greatest transparency. The higher voltage allows even the hottest signals to pass through without noticeable distortion, maximizing headroom. Yet the 676 also features a vacuum tube in the input stage, which means that warm vintage-sounding flavors sprinkled with harmonics can be achieved, as well.

The gain structure of the input stage is handled in a way that allows the signal to be seasoned to taste. Many preamps have two knobs, with one serving as a coarse control, the other as a fine-gain control. In other cases, one acts as a preamp gain, the other as more of the equivalent of a fader. The 676 is set up in a way that is more similar to the latter, while not seeming to follow that design exactly. The first control is decidedly a preamp gain, which can boost a signal and impart tube coloration. When fully throttled, it will cause a subtle harmonic distortion.


The second control, labeled “Post Tube Attenuation,” ranges from “-infinity” to “0,” so my thinking is that this should operate as more of a fader. That said, when driving it too hard, it seems to be pushing the gain, and as it approaches 0 dB, the signal and noise floor rise considerably. Because of this, the smarter play seems to be to gain up the first control with one hand, and then sneak up the second with the other and work back and forth between them until the gain meters at a desirable level while the right amount of tube saturation is accumulated. While this is not immediately familiar territory, setting the gain eventually becomes pretty intuitive, and allows the creation of very clean sounds with little coloration when desired, or warm, melty tube flavors when appropriate.

Illuminated toggling pushbuttons for +48V phantom power, a -20 dB pad, polarity flip and an 80Hz HPF accompany the gain controls on the left of the front panel. The input can be fed microphone-level signals through an XLR jack on the back panel, while a -20dB button on the front of the unit bypasses the XLR input and instead forces the circuit to accept signal from an unbalanced instrument jack on the front panel. I like the idea of using a switch to flip between these inputs rather than using normals, so that the unit can stay racked and connected and toggled when necessary.

Following the mic preamp, the signal encounters the equalizer section. The high and low shelves have fixed frequencies of 10 kHz and 100 Hz, respectively. The midrange band is semi-parametric with a sweepable notch or peak ranging from 100 Hz to 8 kHz. While the Q isn’t fully variable, there is a button to toggle between the default setting and a “narrow” Q mode. Despite the simplicity, given the limited controls for frequency selection and slopes, the little bit of harmonic richness and personality that the components impart allows the whole of the processor to be very useful. Certainly it’s capable of more utilitarian midrange scoops and proximity-enhancing bass bumps, but it really shines when performing more creative augmentation of signals.

The compressor follows a similar story. It has everything necessary to be a low-profile problem-solver while still offering the option of creative coloration. The circuit is based on the design of the dbx 162SL, which bears many of the characteristics common to the whole 160 Series. The low-distortion VCA central to the design of all 160s is found here. Features that popped up in the later models, like manual attack and release time as an available alternative to the automatic envelope-detecting circuit, as well as the OverEasy soft-knee mode, and the PeakPlus limiter, are all available. A ¼-inch TRS sidechain insert is available, the return of which can be used for keying, while a round-trip allows for filtering the source signal before returning it to the detector. For quick, convenient access to a similar function, a handy button labeled “Contour” engages a highpass filter, which simply rolls off the lows from the signal feeding the detector.

While the signal flow is fixed from preamp to equalizer to compressor, connectivity on the back opens up some other opportunities. Following the mic preamp, there is a ¼-inch TRS insert jack, which provides the opportunity for external processing before the source hits the to the equalizer circuit. This presents a number of opportunities, most notably the ability to record the compressed and uncompressed signals independently and blend them together later. I would like to see a dedicated input to the compressor so that the two halves of the unit could be used independently from one another. Given that there is no line-level input to the unit, the only way to use the compressor in a mix would be to sneak an unbalanced signal into the insert return, which sits after the preamp in the signal path.

In Use

The 676 was definitely fun to use. It encouraged experimentation when it came to guitars or drums, but simultaneously provided confident control when trying to convey more straightforward, accurate depictions of sources. I was a big fan of what it could do for musical vocals or spoken word. When dialing in a shrill rock vocal, playing with the preamp drive and equalizer, back and forth, allowed me to add a little bit of distorted bite, but to tune it to single aggressive phrases without compromising clarity and intelligibility. Meanwhile, on an announcer-type voiceover, the same circuit could produce pristine tone with bottom end that could be exceedingly full without threatening distortion. The equalizer was great for clearing out the crowded lower midrange, controlling proximity effect and helping the top end cut through. Once again, playing with the tube drive and the high-frequency equalizer, this time in milder proportions, a splash of harmonics created the perfect finishing touch.

The compressor had the perfect sound for both of these vocal conditions. Setting the attack and release to automatic mode, and working with the hard-knee mode, the speed was just right for tightening things up and adding punch. When it came to the VO, as I kicked the ratio up beyond 3:1 and closer to 5 dB of gain reduction, things became predictably muddy and compressed-sounding. In this case, the Contour button came to the rescue and did a pretty remarkable job of bringing life back to the sound. While tight, punchy percussive sound was useful in that case, the rock vocal merely needed some leveling of its dynamics. Switching to the OverEasy mode stripped away any obvious sign that compression was taking place, A/B’ing the compressor circuit in and out revealed that it was doing a great job of taming the most aggressive spikes.

The unit worked similar wonders when I tried it on a mono drum overhead, and then a room mic. The high-headroom versus the optional drive led to a world of great tonal options. For the overhead, the compressor’s automatic attack and release times again enhanced the punch. Kick and snare blasted through with a controlled sound. The speed was just perfect, and I was never able to match the quick snap of the compressor’s auto mode when switching to manual attack and release. The manual controls, however, allowed more liberties when addressing the room mic. I could slow the attack and get big booming resonances that could be layered under the main drum tracks. Playing with a combination of the release and the Contour button allowed the control to add pumping or hide it. Every sound was great and usable; it was just a matter of choosing which served the track the best.

Plugging in an electric guitar and using the 676 as a DI didn’t disappoint, either. Despite its 12AU7 being similar to what you might find in a guitar amplifier’s preamp section, this unit will not necessarily produce comparable overdrive. No, it doesn’t sound like a distortion pedal. However, when being reasonable and using it to warm up and add a little personality to a guitar before feeding it to a virtual amplifier, the 676 was on point. On top of the great sound of the pre, the compressor did a great job of bolstering the signal so that a software amp’s distortion sounded more realistic.

If you are looking to build an analog processing chain to feed your DAW, this all-in-one solution certainly fits the bill. Each component has a great sound and the flexibility to produce a variety of flavors. Whether recording voice, DI’d instruments or acoustic sources, this strip is a solid performer that will take your solo recordings to the next level.

Try This

The 676 does a great job of turning a drum overhead into an old-school hip-hop drum sample. Drive the input so peaks are just below clipping. Kick up the low shelf and back off the high one. Scoop 200 Hz on “Narrow” mode in the midrange. Use the compressor at 5:1 ratio, 200 ms attack and 4k release, shooting for -5 to -10 dB of gain reduction. Turn the Contour button on and the OverEasy off, and play with the makeup gain and limiter to set a level.

Product Summary

COMPANY: dbx

PRODUCT: 676 Channel Strip

WEBSITE: dbxpro.com

PRICE: $999.95

PROS: A lot of great-sounding options in one portable package.

CONS: Signal flow through the components is not variable.

PAU Audio 805 Mic Preamp

What happens when a hard-hitting drummer with a background in electrical engineering can’t find a mic preamp that satisfactorily captures fast transients? He designs his own. Andrew Hamill, founder of PAU Audio, created the 805 with drummers in mind, aiming for a low-distortion, clean-sounding preamplifier that had enough personality to be musically inspiring. The result is a single-rackspace unit housing four high-headroom preamps whose crystal-clear sound makes them an excellent choice for tracking any kind of instrument.

On the surface, the design is pretty straightforward—no excessive bells or whistles. Each of the four channels has a single large, continuously variable knob with no detents for gain control. Sturdy switches with accompanying blue LED indicators address all other functions. including polarity flipping, phantom powering, and toggling the functionality of a given channel between a mic preamp circuit fed by a rear panel XLR jack and the alternative DI circuit, which accepts signal from the high-impedance, unbalanced, ¼-inch jack on the front panel. The lack of an input pad—circuitry that can risk impedance mismatching—was a deliberate choice in the design. Instead, the input structure is designed to accommodate hot input levels while providing enough gain to treat lower-level signals.

Under the Hood

Apparently, engineers who have heard the 805 have compared it to an API mic preamp. I found this interesting, as a considerable amount of an API preamps’ character comes from transformers and the rest from the discrete op amp. The 805 has no transformers, and this definitely works to the advantage of a preamp designed for fast transient response and low distortion. The top panel should be made of glass so that everyone can see the slick, clean-looking and stylish PCB, loaded with giant capacitors and an array of other components. The other eye-catching feature was the large custom toroidal power supply, which is a key component in establishing high headroom with minimal distortion.

I was surprised when I didn’t see discrete op amp circuits, only unidentifiable ICs shrouded in heat sinks. Apparently the designers auditioned countless discrete and IC op amps, seeking a circuit that performed as well in practice as it did on paper. The eventual winner was an unknown in the preamp game but was chosen for its “pleasant and original” character. I can’t argue with the results, because the 805’s sound is truly unique.

In Use

I first tried the 805 when miking an electric guitar played through a slightly dirty tube amp. I placed a large-diaphragm condenser about a foot-and-a-half away from the speaker in a room with wood floors and a warm, slightly reverberant sound. The 805 captured the amp nicely, in a way that was similar to an API preamp, with a sparkly clarity that didn’t seem to push as much as it merely exposed detail and articulation in the upper midrange. This characteristic showcased the pick’s attack and the harmonics imparted by the amp’s tube gain. The top end was ear catching—so open and clear. I’ve miked guitar amps in that room countless times and don’t ever remember hearing the room sound come through in the recordings like I did with the 805.

The 805 reproduced lower-frequency sounds (i.e., the bottom end of the amp and the resonance of the room) in a way that sounded very true to life. The balance leant itself nicely to a bass plugged directly into the DI input of the 805. Once again, the bottom end was full, and quick thumping notes stayed tight and were never overstated. The buzz and bite of the strings and pickups cut through, providing a clear definition of each note. When designing the 805’s DI function, special care was taken to impedance-match the TS and XLR inputs to their respective input sources. The DI, providing high impedance by using discrete JFET transistors, brings a great mix of rich-sounding, vintage-inspired tone, met with supreme clarity and well-defined bottom end of a modern circuit. Whether using it for bass or electric guitar, the sound was always truly remarkable.

The preamp was impressive when miking any type of drums or percussion instrument. Even in the presence of the loudest hits there was plenty of headroom. I never wound up turning the gain all the way down. The sound was always crisp on top and round and full in the bottom end, without a hint of distortion from the circuit. Drums captured with this pre lent themselves well to EQ and compression in the mix. Any feature of the hit, whether it be the attack or the body of the drum, could be refocused using dynamics processors and stayed pristinely clear due to the clean capture. With other preamps, boosting certain frequencies reveals distortion artifacts that were merely being masked by other frequencies. This never seemed to be the case with the 805.

When using the unit to record speech, the clarity of the consonants and the balanced chest resonance provided a really nice track. The overall sound was clean and quiet enough that it seemed like the 805 might be a good candidate for Foley recording. When recording punches, breaking glass, and other loud, quick sounds, a small-diaphragm condenser and the 805 got the job done very well. There was enough headroom that I could back it off and never need a pad. The 805 proved to be one of the fastest pre’s I’ve heard.

When recording quiet sounds like cloth, I was surprised by how much gain there was. There were a few instances when I felt like I was getting close to maximum gain and still looking for more. There always seemed to be an extra push that came without any noticeable noise from the circuit. The same proved true when using passive ribbon mics. Recording fingerpicked bluegrass instruments like acoustic guitar and banjo, a ribbon mic can give a pleasant old-timey tonality and also keep a banjo from sounding too harsh. Not only did the 805 have plenty of gain, with headroom to spare, but it was the hands-down favorite in terms of sound. Other preamps sounded dark and needed a little EQ to hype the top end, but the 805 made the banjo sound just like it did in the room. All of the top-end detail was there, without being quacky, and once again, the room was perfectly intact.

When recording an acoustic guitar with a condenser mic, I did some A/B comparisons between the 805 and some other transformerless, solid-state preamps. Against a Millennia HV-37, the open, sparkly upper end of the 805 seemed to be a primary difference. The low end from both seemed similar, but overall, the top end of the HV-37 was definitely darker. Granted, the HV-37 could probably have been considered the more accurate sound, but given the nature of the instrument, the coloration of the 805 worked nicely. When compared to the solid-state transimpedance side of a Universal Audio 710, the bottom end of the 805 seemed a bit fuller. Both seemed to slightly hype the top, with the 805 seeming to have a bump around 4 kHz, while the 710 was pushing closer to 10 kHz. Both were interesting and useable but I preferred the sound of the 805 with its more substantial bottom end.

The Verdict

If you have extra line-level inputs on your interface and are looking for a set of preamps to feed them, this could be the perfect solution. Their clean, punchy sound with just the right amount of coloration means they sound good enough that you can just leave the recordings alone, or season them to taste after the fact. Aside from that, you would be hard-pressed to find a faster, better-sounding mic pre for drums and percussion. If your pre’s are flattening out drum sounds or breaking up when faced with loud hits, you have to give the 805 a try.

Product Summary

COMPANY: PAU Audio

PRODUCT: Model 805

WEBSITE: www.pauaudio.com

PRICE: $1,500

PROS: High headroom. Sounds great on a wide variety of instruments.

CONS: No highpass filter.

Brandon T. Hickey is a recording engineer based in Phoenix.

 

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