Warm Audio Bus-Comp

Stereo VCA compressor

Warm Audio Bus-Comp

Review by George Shilling

Since 2011 Warm Audio of Austin, TX have built up quite a range of studio outboard based on classic designs, marketed at bargain prices. The Bus-Comp is no exception. Subtitled a 2 Channel VCA Bus Compressor, the inspiration behind this model comes from the legendary SSL E/G compressor. That much-loved design has of course already seen plenty of re-creations and adaptations by third-parties. The SSL became the sound of pop music during the 1980s, and its characteristics are imprinted on our collective cultural psyche; it endures today in myriad hardware and software forms. Warm Audio’s take aims to authentically copy the original, and adds a couple of extra features.

Warm Audio Bus-Comp

The inputs and outputs are helpfully provided on both XLRs and TRS jacks; some costs have possibly been shaved here – they’re not Neutriks, but the XLRs latch positively and all have gold pins. Additionally there is a single Side-Chain Input using an XLR socket – just like SSL’s own outboard G Series Compressor. In fact, Warm Audio’s Bus-Comp faithfully includes almost all the settings and controls of the original SSL desk and outboard versions. You don’t get the SSL’s Autofade function, but that always was an odd feature for a compressor.


There is an authentic looking black gain reduction meter on the far left, usefully illuminated with bright white LEDs in the bottom corners. It behaves much as anyone familiar with the SSL would expect, with perhaps a little bit more of a bounce. The knobs are logically laid out in the same order as the 1U SSL. Continuous Threshold from -20 to +20 (thankfully no annoying centre detent), There is a familiar six-position Attack rotary switch, then Ratio adds a couple of extra settings, so you get 1.5, 2, 3, 4 and 10. The lowest setting in particular is a useful addition if you want to be gentler. Release has the expected settings from the useful 0.1S fastest to the great sounding Auto setting.


Warm Audio Bus-Comp

Then there’s a whole new knob: HPF. The manual oddly states what an HPF does without explaining the sidechain, but it behaves as expected, rooting out the lows from the detector circuit. Frequencies are 30, 60, 105, 125 and 185Hz (and OFF) and it works a treat, preventing the low end wreaking havoc with stronger compressor settings. Finally there’s a Make-Up gain knob with a range of 0 to +20dB. Big square pushbuttons light up yellow when depressed: Compressor on, External Side-Chain, and Engage Transformers. This plops US-made CineMag transformers into a discrete circuit, changing the character from neutral to flavoursome. Finally, on the far right is the Power rocker; far better having it here than putting it on the rear like the SSL does.

Warm Audio Bus-Comp

Authentically following the original SSL, the Threshold varies with Ratio, so that increasing Ratio actually usually delivers less compression. I gather this slightly odd behaviour was a deliberate design implementation in the original to allow better comparison of different ratios. As with any SSL or clone it is easy to make things pump or grab in a slightly undesirable manner. However, having the lower 1.5:1 Ratio and the provision of the HPF both mitigate that in many situations.


I spent quite some time punching the transformer circuit in and out, trying to work out what it was actually doing. Without precision test equipment, I can’t be sure, but it certainly adds magical enhancement in almost all situations. Most obviously there is added richness to the juicy upper mids where the ear is most sensitive, a sense of scooping out some wallowy muddiness lower down the spectrum, and a tightening up of the bass end. This is a great USP for the Bus-Comp of which Warm Audio are clearly proud: there is even a small CineMag logo printed on the rear panel, although oddly not on the front where you might expect it next to the Engage button. The High Pass Filter also gives the Bus-Comp a big advantage over standard SSL compressors. Setting the filter to 105Hz for a complex yet rocking band mix (with shouty vocals, raucous guitars and beefy drums), with fast release and a lower Ratio of 1.5 or 2:1, CineMag transformers popped in circuit and Threshold set to have the meter waggling around -4 and even heading close to -8 of gain reduction, things glued magically. The Warm Audio did everything expected of it to lend the mix an exciting and rich flavour.


The build quality is good. The silver knobs are a little utilitarian, and I’d have liked a line down their barrels to avoid the parallax that can occur when lining up settings. But everything seems solid, and there’s no reason to think this wouldn’t stand the rigours of daily studio use for many years. Anyone familiar with this type of compressor will not be disappointed, despite the price tag being a very small fraction of the official version. This is my first hands-on experience of a Warm Audio product and if they’re all as good as this, I’m a big fan.

Pros: Incredibly cheap yet authentic replica bus compressor with bonus HPF sidechain and transformer enhancement.

Cons: No lines on knob barrels.