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Warm Audio WA-412

Four-channel Microphone Preamplifier By Neil Rogers
Published January 2018

Warm Audio WA-412

Find out how Warm Audio’s API-inspired preamp compares with the real thing.

Warm Audio have become well known for their affordable recreations of classic mics, preamps and processors. I’ve enjoyed using one of their Pultec-style EQ’s in my studio for a while now, and I’ve heard lots of good things about their 1176 and LA-2A compressor clones. When invited to evaluate their new WA-412 four-channel preamp, I was happy to do so, as the equivalent API unit, the 3124+, has been an important part of my setup for years — but sometimes I’d like a few more channels. As Warm Audio’s offering comes in at less than half the price of the API, I was keen to discover how the two would compare.

First Impressions

The WA-412 is a four-channel microphone preamplifier, housed in a 1U 19-inch rackmounting enclosure. Each channel has the usual complement of controls you’d expect of a professional preamp, including 48V phantom power, polarity inversion, a 20dB pad, and a high-impedance instrument input. Going slightly beyond what you might expect, each channel has a ‘tone’ switch, which changes the preamp’s input impedance, and there’s also an output trim knob, which allows you to drive the input stage in search of coloration form the transformer/op-amp, without overloading the next device in your recording chain.

I’ll confess that while they’ve all sounded decent, I’ve not been a huge fan of the look of the Warm Audio products I own when compared with some of my more expensive kit, and the same can be said here. Aesthetic preferences are, by their nature, highly subjective, though. To offer such designs at such a competitive price, cost savings have to made somewhere — and it’s better to make them in things like the enclosures, which won’t impact on the signal path.

The WA-412’s layout is broadly the same as that of the unit that inspired it, though the gain pots and switches are different in both look and feel. For starters, the WA-412 has a stepped gain control, which is a handy feature, since it allows you to match two or more channels when recording. The switches for phantom power, polarity and so on don’t look the most expensive, but they feel and operate as they should. The last control on each channel is the output trim pot and, like the gain control, this is stepped. This trim should be a very useful feature, as a big part of the character of this style of preamp is what it sounds like when driven quite (or even very!) hard. It’s seemingly impossible to make them sound bad, and they can add a saturated, slightly compressed sound to drums in particular. Although API’s newest version also sports a trim control, my older ones don’t, so they’re routed to a line-level input on my Audient console, which acts as a 20dB pad — without this, I’d struggle to drive the API preamps without overloading my convertors. Still, I actually found the output levels of the WA-412 and my API 3124+ to be quite different, as I’ll discuss in a moment.

Another feature worth mentioning is that the WA-412 features a discrete six-pin op-amp, which can easily be replaced, whether for repairs or in pursuit of your personal holy grail of tone — the API 2520 op-amp is credited with providing a big contribution to the sound of their preamps, and you could, if you wished, put one of these, or one of various third-party designs, in the WA-412. (I’ll leave the heated debates about the relative perceived merits of different op-amp designs to the forums!)

Warm Audio WA-412 rear panel connections.

On Test

There’s only so much you can really say in the abstract about a microphone preamplifier, so let’s move on to how I found it to use in practice, in a recording session at my studio.

Siting the WA-412 immediately below my API in the rack, I switched the XLR inputs over and headed straight into a drum recording session. The initial sound was comfortably familiar, so I proceeded to experiment with driving the channels to see how that might change the sound and feel of the drums. As I touched on earlier, I was a bit thrown by the WA-412’s significantly lower output level: with the gain fully up and the trim-pot left alone, I was just about getting a healthy level through the line inputs of my desk, but on quieter sources I found myself adding extra level via the desk. In setups without a desk or any specific attenuation, this would be a lot more useful, so I suspect that this might reflect the target audience; in a more professional setup like my own it means it feels slightly different when used side by side with high-end preamps that are designed to be used in such an environment. Really, though, this was just a workflow issue, and apart from perhaps encouraging me to drive the gain harder than I might do normally, I quickly became used to it. I was very comfortable that the unit was delivering what it should sound-wise, and on a busy session it felt like it was giving me everything that my API does on drums, guitars and vocals.

In terms of the ‘extra’ features of the WA-412, because of the issue with my setup I never really needed the output trim, but many users should find it very useful indeed. I played around with the ‘tone’ switch, which affects both the mic and instrument inputs, but found the difference to be a bit inconclusive during the sessions in which I tried it. The theory is that by switching the input impedance between 600Ω and 150Ω, you can achieve either a ‘thicker’ or ‘cleaner’ tone, depending on what mic you’re using — ribbons and moving-coil dynamics are far more sensitive to changes in impedance than capacitor models. In practice, it felt like it was perhaps adding a touch more low-mid to a snare or electric guitar with the tone switch in, but the changes were not dramatic. (See if you can hear the difference yourself in the audio examples provided in the ZIP download — see sidebar at right).

The Warm Audio WA-412 happily sat in the rack throughout the review period and was used on a number of recording sessions. As a testament to how similar the two units sound, I can let you know that my fellow engineers and I never felt the need to spend the extra two minutes plugging our API unit back in when setting up for a session. This might be a general comment on the degree of difference between good preamps designed around a similar theme — but I honestly would struggle to tell enough of a difference to care.

Before handing the unit back, I had a bit of downtime to do a proper A/B comparison between the Warm Audio and API units. Dusting off my drumsticks, I recorded a few short passages of rock drums through each unit. I aimed for consistent performances while varying the amount of gain applied between conservative and driven into the red on the LED. I also managed to persuade Sam Inglis to throw down a bit of guitar, via a DI, which I was then able to reamp with various levels of gain applied by the two units. On a very close listen, when the gain is at a conservative level they sound very, very similar to me. When driven into the red, I feel that the WA-412 is a touch brighter, and possibly just a touch more ‘harsh’ as a result, but this is nit-picking really — check out the full set of audio examples and listen to the differences yourself.

Summing Up

Setting aside the API comparison and considering the Warm Audio WA-412 as a product in its own right, I have to say that it offers great value, given that there are four excellent-sounding, discrete, stepped-gain preamps. They do ‘clean’ well enough, but they also respond nicely to being driven for a little more tonal contribution.

If you’d prefer to consider how this preamp compares with its muse, then I’m confident that it sounds close enough that people would struggle to tell much difference in a properly set-up blind test. My only real criticisms when comparing the two would be my personal preference on the styling, and that difference in output level — which is not such an issue in its own right, but it could be a minor annoyance if you were looking at the WA-412 to augment an existing API setup.

If you like the sound of this style of preamp, and need four channels, then you’d be hard pushed to find anything as good as this for anything like the price, whether rackmount or in the 500 series.


API’s 3124V updates my 3124+ with an output attenuator, and for similar money the Millennia HV-3D and Neve 1073-inspired Vintech 473 are worth consideration. Less costly, though pricier than the WA-412, are the Daking Mic Pre IV and the SSL Alpha VHD Pre. Closer to the WA-412 in price is the Focusrite ISA 428 MkII. Slightly more affordable, the DAV Electronics BG2 MkII is of high quality but lacks some of the WA-412’s features.


  • Sounds great.
  • Stepped gain controls.
  • Output trim.
  • Op-amp can be replaced easily.
  • Price.


  • Output level could be hotter.


Warm Audio have produced a well thought-out, great-sounding four-channel mic preamp that captures the sound and flavour of a classic design, and offers great value to boot.


£1150 including VAT.

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