Mix bus, meet your new best friend.

The Black Box Analog Design HG-2 is a line level, stereo unit designed to add saturation, harmonics, natural compression, increased RMS and enhancement during mixing and mastering. It is designed to easily and naturally do what usually requires multiple pieces of gear and do it better!

Tubes, transformers & tone!

The HG-2 uses custom input transformers to feed two paths: The main signal path travels through a 6U8A Pentode tube stage that then drives into the Triode stage that follows, resulting in everything from subtle harmonics to full on saturation.

Also fed from the input transformer is a parallel signal path that utilizes a set of 12AT7 tubes, voiced specifically for harmonics and saturation. This parallel saturation circuit is outfitted with a 3 way “Freq. Select” switch that allows the user to choose the frequency content returning from the circuit. The “low position saturates just the low mids and sub frequencies, the “flat” position saturates full bandwidth and the “high” position saturates only the high mids and high frequencies. The result is the ability to add top end to dull tracks, enhance low end or enhance and add energy to the entire signal. The “saturation” knob allows the user to control how much of the processed, parallel signal is fed into the main signal before hitting the Pentode stage. Finally, both stages reach the passive output attenuation before a pair of custom output transformers.

In addition to the saturation stages, an “air” switch adds a subtle top end lift and the “alt” tube button switches between two different 12AT7 tubes in the parallel circuit. Switching between tubes allows the user to select between differently voiced tubes for different types of saturation, instantly.

The meter button switches between 3 modes (VU, VU/Peak & Energy), and the “bypass” switch is a true bypass that shorts the input directly to the output with no additional circuitry in line.


Click "+" for detailed description of each control

1. Power switch

On/Standby/Off positions.  Standby mode sends power to the tube heaters and LEDs.

2. Parallel Saturation Frequency Control

Three position selector allows the user to filter the parallel saturation circuit before it mixes back into the main signal path.  “Low” saturates only the low mids and low frequencies, “high” saturates only the high mid and high frequencies and “flat” saturates the entire signal.

3. Parallel Saturation In/Out

Brings the saturation circuit in or out.  When “out”, saturation knob has no effect.

4. Parallel Saturation Pot

Volume control for output of parallel saturation section.

5. Alt tube selector

Selects between two sets of 12AT7 tubes in the parallel saturation section.  The “alt” tube is voiced more aggressively.

6. Pentode gain

Attenuation pot comes before the Pentode gain stage, allowing the user to drive into the tube.

7. Meter mode

Push button selector toggles between three meter mode.  Mode 1 is vu, mode 2 is vu with peak hold, mode 3 shows energy moving outward from the center of the meter.

8. Triode gain

Attenuation pot comes before the Triode gain stage, allowing the user to drive into the tube.

9. Air button

Brings the air circuit in or out.  When engaged, “air” adds a harmonic lift starting around 10k.

10. L/R trim

Very fine (.4db per side) left/right balance adjustment.

11. True bypass

Hard bypass shorts xlr inputs directly to xlr outputs for true bypass.  Note:  The meter is still active but fed from a buffered circuit so as to not add distortion or loss of level.

12. Output attenuation

Fully passive output attenuation located directly before output transformer.

Signal flow


Click here for PDF manual.

Black Box Analog Design: HG-2 Tube Processor

Tape Op Review by Scott Craggs

So, what we have here is a big (3RU-height), heavy (26 lb) black box filled with tubes and transformers, from a company called Black Box Analog Design. That’s a lot to like already, and I haven’t even told you what it does yet.

I’d been extremely curious to check out the HG-2 ever since I first saw it mentioned online awhile back. Robert Wainscott and Eric Racy, the brains behind BBAD, were happy to send over a unit for review, and I put it right to work in my mastering chain. The initial half-hour test session was enough to convince me there was no way I was giving this thing back.

So, what does it do? BBAD bills it as “your mix bus’s best friend.” It can add harmonics, increase RMS level, tame peaks (gently or not so gently), and do full-on distortion if that’s your thing. It’s mainly designed to process complex 2-channel mixes, but naturally, it works great on submixes or individual channels too.

The heart of the HG-2 (Holy Grail? Harmonics Generator? Hits Guaranteed?) is its two gain stages, Pentode and Triode. Pentode feeds the Triode, and you can get a wide range of tones just playing these two gain stages against each other and/or against the output.

That alone would be cool enough, but there’s also a parallel saturation circuit, enabling you to blend in any amount of distortion (from barely audible to completely ridiculous) with the main signal. And you can choose from two different types of tubes for this circuit, one voiced more aggressively than the other. And, you can choose to have this parallel distortion be either broadband or targeted at the low or high frequencies. Nifty!

Besides that, there’s also a simple Air switch, which adds a smooth, high-frequency boost. The boost is at a fixed level, but you can adjust that level via an internal trimmer. I’m the rare mastering engineer who thinks “air” is overrated, so I was initially dubious about this feature, but hey, I was wrong. More on that later.

Before I dropped the HG-2 into my rack, I opened it up for a look inside. I am a very untechnical person; I can barely tell a capacitor from a resistor, but I can tell you that the inside of the HG-2 is a thing of elegant, simple beauty. It looks lovingly assembled, the faceplate is super thick, and the whole thing seems totally bulletproof.

So, tell us how it sounds already. Hang on, before we get to that, let’s talk about the ergonomics of this thing. Because the ergonomics are great. It’s laid out in a really smart fashion. There are big knobs for Pentode, Triode, Saturation, and Output. Unity gain is Saturation off, Pentode and Triode at noon, and Output at about 2–3 o’clock. In practice, I found a good starting point was usually Pentode at 2:00, Triode at 1:00, Output pulled back to about noon. You can do that with one hand motion in 2 seconds. The bypass switch is located right under the Output knob. You can toggle this with one finger while adjusting the output level — super helpful for doing level-matched comparisons. Likewise, the in/out and type switches for the Saturation circuit can be switched with a finger while you’re adjusting the knob. Maybe this stuff doesn’t sound like much in print, but in practice, it’s all really useful, and evidence of smart design by actual working engineers.

Anyway, the sound. At unity, it’s very transparent; you can barely tell it’s there. Once you start pushing the gains around though, the fun starts. I’m going to try really hard to avoid overused buzzwords here, but basically… big, open, wide, rich, vibrant, lively. That’s how it sounds.

By playing with the Pentode/Triode gains, and the Parallel Saturation, you can get a lot of level. A lot. Like, enough where you don’t need a limiter to get up to… ahem… “commercial” loudness. Initially, this was of course very appealing! But once I regained my senses a little bit, it was clear that this was not really the best way to use the HG-2. Rather than using it to get all-out level, it’s much better to use it for tone, and to view the increased RMS and tamed peaks as nice byproducts, rather than the goals.

The Pentode and the Parallel Saturation both feed the Triode, and with too much gain going into the Triode, you’ll get obvious distortion — and not the kind you want — so you need to pay attention. But at reasonable settings, you get a bigger, richer version of the mix you sent into it. And who doesn’t like that?

As mentioned above, I generally find Pentode around 2:00 and Triode around 1:00 a good starting point. But, it varies a lot depending on the mix. There’s a sweet spot on the Pentode around 2:30, where everything just all of a sudden seems to go “whoosh,” and the level comes up dramatically. Sometimes that’s great, other times I prefer easing up on the Pentode and leaning into the Triode. With moderate gain going into the Triode, you can crank it all the way up without any noticeable distortion, and this can lend a really smooth, velvety texture to mixes that’s very seductive.

The Parallel Saturation is also really useful. I was initially a bit dubious, as I tend to think saturation (parallel or otherwise) is overrated in mastering (most things in mastering besides EQ are overrated, but I digress). However, I was wrong. It sounds great, and it works really well on a wide range of music, from metal, to folk, to hip hop. Used judiciously, it doesn’t sound like “distortion”; it just makes mixes sound fuller and more up-front, and brings up low-level details in a nice way.

I tend to use Saturation in “normal” mode, but the Alt Tube setting (voiced more aggressively) finds its way on some tracks, and it’s great to have the option at the push of a button. Likewise, I mostly use Saturation in broadband mode, but the Low mode has be really helpful on thin-sounding mixes; it adds some nice weight in a more transparent way than piling on a bunch of EQ. I don’t use the High mode too often, but there were a few mixes where it worked out well, and again, it’s great to have the option.

That brings us to the Air circuit, and as mentioned above, I was skeptical at first. I don’t use this that often, as I tend to just use good old fashioned EQ to brighten things up, but again, having the option at the press of a button is great. You know, just press it; try it out. So simple — and on the right mixes, it sounds wonderful.

I mostly use the HG-2 in a mastering context, but I wanted to try it out on some individual tracks as well, so I took a couple of my own songs-in-progress and experimented with running tracks and submixes through it — mostly guitars, vocals, and bass. It worked well in all cases, and it was quick and easy to find appropriate settings. It really shined on bass. I don’t remember exactly what I did, but I think there was a pretty healthy amount of saturation added, and it worked wonders for getting a nice, full bass sound that was very present in the mix, without overpowering everything else. No small feat!

Somewhere up above I used the word “fun.” Let me say that again. This thing is fun to use. It’s quick, it’s intuitive, it’s musical, and it sounds awesome. There’s just the right amount of options. Besides the sonics, the fun aspect is the best thing about the HG-2. There are no numbers anywhere on it; you’ll never know how many dB this or that you’re doing. You just turn the knobs until it makes you happy. We need more boxes like this. Less thinking, more listening.

In the interest of being “fair and balanced,” am I supposed to say something bad about the HG-2? I got nothing. I think it’s terrific. It does pretty much exactly what I’d hoped it would, and I think it very nicely fills a void in the marketplace. We have zillions of EQs and compressors already, and while there are some other “nicerizer” boxes out there, I don’t think any of them are as versatile as the HG-2. When I was initially thinking about this review, I was going to talk about how far plug-ins have come in the past couple years, and how we now have some truly amazing EQs and compressors available in-the-box. The one area where plug-ins have left me wanting is distortion/saturation. I’ve tried a bunch and haven’t liked any of them at all. Which is why I was so anxious to get my hands on the HG-2; I was pretty confident it would be a really helpful addition to my mastering rig. It has proven to be just that, and I ended up purchasing the demo unit. Well, as it turns out, Robert and Eric at BBAD weren’t happy with the state of software-based saturation either, and they’ve teamed up with the folks at Brainworx to come out with a plug-in version of the HG-2. At the time of writing, I haven’t heard the plug-in version, but I’m going to guess that (1) it sounds great, and I’ll love it, and (2) I’ll still continue to use my hardware version, simply because it fits into my mastering workflow so well, and turning knobs is just always going to be more fun than clicking and dragging to turn virtual knobs on a screen. But having multiple instances available for individual tracks would be great, and I’m looking forward to checking out the plug-in.

In all, I can’t recommend the HG-2 highly enough. It’s hard to imagine anyone being disappointed with this thing. It’s not cheap, but for what it does, it’s a bargain. The demo recordings on the BBAD website give a good idea of what it can do. Check those out, then get one to try for yourself.


  • High voltage Pentode & Triode tube stages
  • Parallel saturation with mix control
  • Selectable parallel saturation frequency
  • Instantly selectable saturation tubes
  • “Air” lift
  • Ultra fine L/R trim adjust
  • Custom input and output transformers
  • True bypass
  • Selectable 30 segment meter (3 modes)
  • Illuminated push buttons & sealed relays
  • Internally modular design for easy servicing