Saturday, April 20, 2024


Locomotive Audio is a boutique audio equipment builder in St Louis, Missouri (my old home town :-). Their products are hand made in very small numbers so they can deliver old-school quality, beauty and ultra-high performance.

The 14B Vari-Mu by Locomotive Audio

The 14B is a 2U, vacuum tube powered vari-mu compressor which incorporates original design features with vintage design elements. If you mix outside the box, you'd better put seat belts on your ears because this compressor inserted on the lead vocal track will blow your mind. 

I've tried the 14B on a number of different sound sources but inserted on the vocal track during mixing is my favorite use by far: the 14B provides a HUGE sound without the usual artifacts a FET or VCA type compressor can impart. Once I started using the 14B on a vocal insert it immediately made me want more of them so every vocal could have its own 14B compressor. 


Hinged front panel, knurled knob holds it in place

The 14B chassis and metalwork take design cues from classic pieces like the Gates Sta-Level and the Teletronix LA2; the hinged front panel folds down to reveal the inner electronic workings. I'm not sure what the reason for this hardware design is but I like it. Also, like the vintage hardware the tubes and transformers are mounted on the rear of the 14B; this gets all the heat generated by the tubes outside the box with lots of air space around the hot glowing glass bottles. Mounting the tubes on the rear panel also makes them more subject to accidental breakage or possibly melting cables that get too close in a crowded rack.

14B rear panel power package, R to L, in/out XLR's, Mu metal transformer cans, preamp tubes, 6V6 pair of output driver tubes, massive steel output transformer

On the front panel is the gorgeous glowing Sifam VU meter which is used to show gain reduction and output level. A switch is provided right below the meter to select which signal is indicated, “gain reduction” or “output level”.

Input and Output level knobs on the front panel are larger than the knobs used for setting Attack and Release times; the Side-Chain Low-Cut is an even smaller knob. Four miniature switches are joined by one large and substantial toggle switch which turns power On and Off; a big jeweled pilot light completes the vintage styling. 

XLR Input and Output plus unbalanced stereo link 1/4" phone jack

The rear panel is crowded with tubes, transformers and XLR input and output jacks. Also on the rear panel is a 1/4” phone jack which is used to link two 14B hardware units together for stereo operation. 


In use the 14B does not disappoint, it has sounded great in every application I've tried so far. Vari-Mu compression and limiting sounds different from all the other “gain reduction methods” (FET, VCA, & Optical). The 14B audio output is never dull, it's always sweet and pleasant without the slightest bit of harshness. Putting one of these on your lead vocal can help it blend perfectly into a mix, full and punchy sounding without destroying the overall dynamics of the performance. 

In use the 14B does not feel as fast as some of my FET compressors and not as aggressive as some VCA compressors but the results never disappoint. The 14B keeps the sound BIG in spite of the gain reduction it is capable of delivering. 


One of my other Vari-Mu compressors is the “Weight Tank” which is also produced by Locomotive Audio. The Weight Tank is a great sounding compressor which uses the same remote cut-off, variable-mu vacuum tube as the 14B; this might lead you to think they're similar in performance. While the Weight Tank and the 14B share some similar sonic characteristics the 14B hits harder, it cuts deeper and faster, has more useable range, delivers bigger tone and sound than the Weight Tank when used in identical mixing situations. Just as a painter uses different brushes and paints to achieve specific color effects the Weight Tank and the 14B have different applications where each shines brightest. 

The output section of the 14B is like a 20-watt push-pull guitar amp powered by a pair of 6V6 power tubes. The output section of the Weight Tank is more like a 1-watt guitar amp. The Weight Tank is sonically similar to the highly coveted Altec 436 (think Abbey Road, Beatles), a very capable variable-mu compressor. The 14B sounds like a vintage tube Sta-Level on steroids, with faster, deeper gain reduction and always HUGE tone. You may have noticed some solid state FET and VCA compressors make your tone sound small while trying to keep levels in check, this is never a problem with the 14B no matter how hard you push it.


  • Only two rack spaces
  • Tubes on back for better cooling
  • Heavy duty vintage style hardware design
  • XLR Input and Output


I like the 14B A LOT. I'm thankful Locomotive Audio sells factory direct or else this vintage styled compressor would cost 30-50% more through retail dealers. At the current price it's a stretch for a typical home studio but if you're looking for a one-of-a-kind vocal processor (or an anything-compressor) this all tube model is a bargain in the modern marketplace. It is a treat to use the 14B, it brings broad smiles and joy every time I power it up in any mix. 

Thank you for reading High on Technology, Good Music To You!

©April 2024 by Mark King, it's not ok to copy or quote without written permission from the author.