Heritage Audio: Grandchild 670-500 Compressor

There’s an age-old philosophical question in the audio community: “If a Fairchild compressor/limiter falls in the woods and loses over two dozen tubes and transformers, is it still a Fairchild?” Where does innovation end and compromise begin, and is it even worth attempting to pull off something this ambitious? The elephant in the room, though, is that most of us have never worked with a real Fairchild, something I’ve been able to do only a handful of times – but that’s not even near enough experience to speak with any authority on this subject. Keeping this in mind, my approach to Heritage Audio’s two space 500 Series Grandchild 670 vari-mu stereo compressor was simple: Does it sound good and do what I want a vintage-style variable-mu to do?

My first test was listening to the “box tone” of the Grandchild without any compression. If you’re looking for the Grandchild to do something along the lines of the Manley Variable Mu (where your source sounds noticeably different by just passing signal), you should probably keep looking. The Grandchild seems pretty transparent, even when driving the input quite hard. That’s not a good or bad thing; it just depends on what you’re wanting out of your compressor. After a few weeks, I was hearing an extremely subtle high end roll-off when using the Grandchild on brighter sources or the mix bus. It’s sweet and warm, but not something I would say is a feature of the unit. As far as frequency response and harmonics, it’s fairly clean by design.

The Time Constant options also differ slightly from the original Fairchilds, which is definitely a step in the right direction, in my opinion. The first setting is what Heritage is calling the “Ardent Mod,” named after Ardent Studios [Tape Op #58], where everyone from Led Zeppelin to The White Stripes has recorded – quite the history! There’s a lot of lore behind Ardent's modifications to their in-house Fairchilds, but in essence, they had some of the Time Constant settings modified to be quicker and more useful. I’ve never really used the higher/longer Time Constant settings on any Fairchild design, so an option like this is a welcomed rarity.

Time Constant 1 on the Grandchild is an instant and familiar sound when used on acoustic guitars; it just sounds right, and apparently, it was what Jimmy Page always requested on his acoustic guitars. If there’s one single takeaway from this unit, I think Heritage nailed that part. From there, Time Constant 2 becomes the original Fairchild's first setting, with the rest following suit.

Let’s talk about what I believe is the essence of the “Fairchild Experience.” There’s a lot going on under the hood, but you have very little control over many parameters. You pick a couple of settings and use your ears. I find myself realizing after the fact that I’m being a lot more aggressive with the Grandchild than I would with other compressors that let you fine-tune many parts of the compression process. You also realize after a while that a seemingly simple design has the potential to be extremely flexible when you get better at understanding all the intricate interactions. This leads to my biggest complaint: Like the original Fairchilds, the Grandchild does not offer an output control, which can require post compression make up gain during tracking, or when pushing the Input hard. The DC Threshold essentially varies the ratio and compression curve (knee). When turned fully clockwise to the right, you begin in compression territory, then gradually move to more of a limiter ratio as you turn counterclockwise to the left. When setting your input gain to match your original signal, you’ll have no problem getting more than enough compression with the DC Threshold set between around 1:00 and up to the default 5:00 setting. If you want to get into heavier limiting territory (such as crushing drum room mics), you must drive your input gain so hard at times that you’ll be clipping your converters. In my case, I’ve got the Grandchild in the 500 Series slots of my API Box console [Tape Op #101], so I’ve got faders to compensate on the output side of things. However, to get the most from your Grandchild, I would suggest you budget for some sort of attenuation device to manage the compressor’s output. (On the other hand, the Grandchild is one of the few 500 Series units we've seen with a power switch on the front, allowing one to turn it off when not in use to save tube life and reduce heat output. -Ed.)

I also found it frustrating that the three position high-pass sidechain filter is on the side of the unit, which means you have to take the Grandchild out of the 500 Series chassis to change it. There were times when the filters worked perfectly for something like mix bus duties, and other times when they made the Grandchild react differently at the detection circuit. A simple flip of the switch solves that, but the positioning could be more convenient. For most instances, I kept the sidechain off, except for mix bus duties alongside the API 527 compressor built into my console.

Compromise isn’t always a bad word – it makes options like the Grandchild a reality. I can’t be the one to tell you whether or not some of those compromises are going to be things you can work around for your situation. What I can tell you is that there are not many options in this format or price point, and the fact Heritage was able to pull this off at all is impressive in and of itself. There were a few moments of frustration where I couldn’t quite get the Grandchild to do what was needed, but many other instances where it put a smile on my face and sounded flat-out awesome. Though this unit is not a Fairchild in every way, it often gets close to the real thing. I also can’t afford to spend as much on one compressor as I did on my whole recording console, which makes most of those compromises easier to swallow!