by Bob Malkowski | 4,6 / 5,0 | Approximate reading time: 5 Minutes | Our Rating: 4,5 / 5,0

 ·  Source: WARM Audio


We review the WARM Audio WA-MPX, a tube mic pre and DI box promising the sound of the tape machines that birthed rock and roll. Can a tube pre at this price point really deliver warm, girthy, vintage tube tones? We took one for a test drive…


WARM Audio WA-MPX – Standout Features

  • Recreation and update of the AMPEX 351 tube preamp
  • Mic preamp, line input and instrument DI
  • High and low pass filters
  • Switchable gain modes for tube saturation
  • Phantom power
  • Switchable input impedance/tone
  • Warm analogue tube tone with huge headroom


We’re big fans of WARM audio’s accessibly priced microphones, preamps and audio gear, hear at Gearnews. The WA-MPX is the latest in a line of commendable recreations and re-interpretations of vintage and classic audio gear. We covered the WA-MPX when it was first released in March 2023, but now, thanks to the nice people at WARM Audio, I have one in my hands to put through its paces!

50s Tech for the 21st Century

The WA-MPX is based upon the pre-amp and electronics of the legendary, 1950s AMPEX tape machines.  These early machines found their way into the hands of recording pioneers such as Les Paul (yes THAT Les Paul) and Sam Phillips of Sun Studios. Sun Studios is famous for the breakthrough Rock and Roll recordings of artists such as Elvis, Johnny Cash, and Jerry Lee Lewis.

As time went on engineers took to separating the audio electronics from the tape transports of the AMPEX 351 and repurposing them as standalone tube mic preamps. So what we have here then, with the WARM Audio WA-MPX, is a modern recreation of the AMPEX 351 tube signal path but purpose-built as a tube microphone preamp.

Warm Audio WA-MPX and WA-2MPX

Meet the Warm Audio WA-MPX and WA-2MPX preamps! · Source: Warm Audio

First Impressions

Pulling the WARM Audio WA-MPX from its box, my first impressions are of a solidly and well-built piece of kit. Each of the front panel toggle switches flicks into place with a hefty and reassuring “klack”. Equally the gain and output level knobs are smooth and pleasant to use. I get the impression your money isn’t being spent on vintage correct bakelite knobs and so on. Instead, you’ll be buying a nicely made, workmanlike pre-amp.

One thing I should mention is that you must use the WARM Audio WA-MPX with balanced cables. I initially plugged up using unbalanced patch leads which led to odd behaviour from the VU meter and output control.  A quick chat with the helpful bods at WARM HQ confirmed the WA-MPX must be used with balanced connections only.

Big, Bold, and Warm

First up, I plugged up my “day-to-day” mic, an Earthworks ETHOS condenser mic. Flicking on the phantom power switch and dialling in some gain, you are instantly rewarded with a smooth rounded tone with lots of low-mid heft. If you use a low-output dynamic mic, then the “high gain” switch comes into play, making dynamic and passive sources really come to life.


Next, I grabbed a bass guitar and plugged in directly using the dedicated Instrument input. I’m not exaggerating when I say that tracking bass with nothing more than the WA-MPX gave me the best DI’d bass tone I’ve ever recorded! Thick, round, weighted, and yet still with lots of clarity, this tone is arguably worth the price of admission alone. I then plugged in my telecaster and was equally surprised at the warm, round, articulate tone.

Warm Audio WA-MPX

WA-MPX · Source: Warm Audio

Down and Dirty

You’ll find that to get the best out of the WA-MPX, you’ll need a solid understanding of gain staging. There’s an obvious “sweet spot” of input gain just before obvious distortion sets in. Here’s where that famed “tube magic” takes place. With that said, there’s value in the more extreme settings, too…

Switching to the line input, I ran a Minimoog bass line through the WA-MPX directly from my DAW. Again, the clean tone took on a weight and presence that really helped it in the mix. Flicking in the ‘Tone” switch adds some gentle saturation and colouration which is very pleasant. Then I eyed up the option labelled “Tape Sat”…

Tape Sat is intended to simulate tape saturation, the effect of having a very hot signal going directly to tape. I have to be honest here and say that, to my ears, it doesn’t sound much like tape saturation! What it does sound like, is high-gain tube filth, and in that respect, it’s a very usable effect. Using the tube sat option to dirty up synth lines, for example, is a deeply wicked and deeply enjoyable experience!

A WARM Impression

So then, is the WARM Audio WA-MPX another strong addition to WARM Audio’s line-up? Absolutely! While arguably not the most versatile pre-amp you’ll ever buy, it does have one overwhelming character: It’s a “go-to” unit if you want to add girth and heft to any source. I loved what it did to my voice when tracking and as mentioned, this is a phenomenal unit for tracking DI’d bass guitar!

If you’re looking to add some authentic tube warmth, dirt, and grit to your recordings then it’s hard to think how you could go wrong at this price.

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Warm Audio WA-MPX
Warm Audio WA-MPX
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3 responses to “REVIEW: WARM Audio WA-MPX – Vintage tube warmth at a bargain price?”

    Steve says:

    Thanks for the review, it sounds like a great pre amp. If I had the money I’d buy both a single and stereo version! 🙂

    Euphemia says:

    Do you need to use a balanced cable to input into the D.I. ( from your bass guitar ) ?

      Bob Malkowski says:

      The “Instrument” input on the front panel is an unbalanced TS input. You can (and I did) use a conventional guitar lead straight into the Instrument input on the WA-MPX.

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