Heritage Audio Grandchild 670

From the Spirit of the HERCHILD to the 500 Series: a "large format" signature in a compact module

After making a strong impression with the HERCHILD Model 670 and Model 660, Heritage Audio brings this tube compression philosophy to a more accessible and easily integrated studio format: the 500 series. The GRANDCHILD 670/500 retains the core goal of the range, which is to capture that sought-after analog character while making it available in a compact two-module chassis. This precise positioning is what makes it interesting: to rediscover the "Fairchild"-type response and an organic compression feel without having to use a bulky rack-format processor.

A stereo compressor designed for mixing, bussing, and demanding tracking

The GRANDCHILD 670/500 is aimed at sound engineers, producers, and advanced home studio users who want musical stereo compression capable of adding density, glue, and texture to a drum bus, instrument bus, stereo synth, guitars, or even a mix bus when seeking a warm imprint. Its Variable Mu design emphasizes a natural and progressive action, ideal for controlling dynamics without crushing the sense of movement, while adding the harmonic richness typical of tube stages.

Controls, curve, and sidechain: compression ranging from firm limiting to transparency

True Variable Mu, NOS tubes, and dedicated transformers

At the heart of the module is an authentic Variable Mu compression topology: two NOS 6BA6 (5749) tubes per channel, paired with three transformers (one per channel and one for the sidechain circuit). This construction aims to reproduce the elusive response and behavior sought after: compression that can be broad and authoritative, yet surprisingly smooth when set for subtlety.

Settings inspired by classics, adapted to modern workflows

The INPUT GAIN control offers an adjustable range of 20 dB, useful for calibrating input level and pushing the compression stage according to the desired color. The AC Threshold sets the working threshold, while the selection of 5 attack and release times facilitates adaptation to the source: from fast hold to tame transients to slower times that preserve punch while thickening the signal.

DC Threshold: continuous progressive slope

The DC Threshold provides access to progressive ratio behavior, a particularly musical approach when you want to avoid the "brick wall" feel typical of some harsher compressors. Here, the adjustment acts like a curve combining ratio and knee concepts: you can go from firmer limiting to very soft and transparent compression, with a smooth transition that remains pleasant on complex signals.

3-position sidechain high-pass filter: stable lows, a breathing mix

Essential for modern productions, the 3-position sidechain high-pass filter reduces the influence of low frequencies on the detection circuit. The result: the compressor reacts less to kick drum hits or overly dominant bass notes, helping to preserve the low-end foundation while achieving more consistent and "mix-ready" gain reduction.

VU meter, bypass, and 500 series ergonomics

The VU meter allows quick visualization of the processing behavior, useful both during tracking and mixing. The bypass switch facilitates instant A/B comparisons, essential for dialing in the right compression level and validating the musical impact of the processing within the context of the track.

Technical specifications

Category	compressor	Rack unit	2
Number of channels	2	Color	Black
EQ	No	Weight	1.12 kg
Valve	Yes	Dimensions (mm)	180 x 133 x 75

Input Gain	20 dB adjustable range	Dimensions	133 x 180 x 75 mm (H x W x D)
Power	16-16 V AC