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Review by Dave Johnston: dbx 676 Tube Microphone Preamp Channel Strip

Posted by Tim Robertson on

In its 45th year producing professional audio equipment, US manufacturer dbx has added the 676 Tube Microphone Preamp Channel Strip to its arsenal. A small group of staff and students from SAE Creative Media Institute were able to put this new unit through its paces in the Classic Studio at SAE’s Auckland campus.

The 2U rackmount unit comes with a high­ voltage, Class­A tube preamp section, a 3­band semi ­parametric EQ and a compressor/limiter based on the famous dbx162SL. dbx are aiming their sights at both the recording and live markets with the 676 , boasting military­ grade build quality with vintage inspired controls, VU metering and an optional state­-of-­the-­art digital output card (which wasn’t released at the time of our testing).

The pro­audio market already has a handful of tube preamp & channel strip units available, with offerings from brands such as Universal Audio, Avalon, ART, PreSonus and several others. While dbx aren’t necessarily breaking new ground with their addition, they do have their rich history in dynamic processing to bring to the table, and they say the 676 represents the best of it.

The tube preamp section offers a lot of tone flexibility. The two dials, for gain and for post­ gain attenuation respectively, work together to achieve the desired amount of drive while enabling a decent signal level through to the EQ and Dynamics sections. In our tests, we were able to dial in anything from crisp clean tones right through to annihilation style drive, with many usable drive stages in between. There is a red peak light, useful for warning the user when output level needs to be pulled back with the attenuator, though an orange drive light could have been a useful addition for an extra visual indication of what’s going on when looking for just a touch of saturation. This is a minor gripe though; this is a solid, musical sounding preamp overall.

Next in the chain is the 676’s EQ module. It has low and high shelves, as well as a sweepable mid­-band (100Hz ­ 8kHz) with a ‘Narrow’ button that toggles bandwidth between wide (Q = 0.9) and narrow (Q = 2.9). Chances are you’re not going to use this EQ for surgical audio correction, so these options give more than enough control for tone shaping on the way in.

With dbx’s legendary dynamics background, you’d expect the compressor section of the 676 to impress. Having been developed based on the legendary 162SL, it doesn’t disappoint. It can provide very transparent compression, and could be used effectively on a wide range of applications. In our trials, subtle compression evened out our vocal takes nicely, and combined with a touch of flavour from the preamp the vocals instantly sat well when added to the instrumental mix. With extreme settings dialled in, we were able to completely annihilate peaks on a bass guitar DI signal without undesirable artifacts. You might expect some compressors to leave you with nasty clicks and pops when cranking the attack knob right up, but not in this case.

The compressor’s attack and release dials are labelled in a very technical manner which may be a little confusing at first, being measured in dB/ms as opposed to a more common time scale. While they could have made it a little more straight forward, this labelling is consistent with their 162SL, and indeed the classic 160SL , so it is understandable that dbx would want to maintain the style of their legendary models.

Due to its sheer versatility, the 676 would be a great addition to the studio for anyone looking to invest in a quality mono analogue input option for a touch of flavour on the way into their DAW. Adding a touch of analogue colour and some tasteful EQ & compression at the recording stage will allow your tracks to sit better amongst instrumentation from the get go, requiring less work in the mix. Having the 676 available as a hardware insert means that use of real dbx 162SL style compression is at your fingertips for any mono instrument, brilliant for lightening fast characteristics that are hard to achieve with plugins.


Dave is the Industry Liaison at SAE Auckland. He is also a musician as well as a freelance music producer & audio engineer.


Click here for more information on the dbx 676

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