You are here

Warm Audio WA-1B

Valve Optical Compressor By Bob Thomas
Published December 2023

Warm Audio WA-1B

The war of the clones shows little sign of ending — and Warm Audio have now trained their sights on a very classy optical compressor.

The WA‑1B is the latest release from Texas‑based Warm Audio, and it’s described in the manual as being “an accurate recreation of a world‑class Scandinavian compressor combining smooth tube‑optical warmth with precision controls.” The model number, cosmetics and controls make it pretty clear that its muse is the renowned Tube‑Tech CL‑1B. Made by Danish manufacturers Lydkraft, that device is a single‑channel, transformer‑balanced, valve‑based optical compressor, and it’s been in continuous production since 1991. Its lengthy lifespan (32 years and counting) would qualify any piece of studio hardware as a ‘classic’, but it arguably earned that reputation earlier than most, and I am somewhat surprised that it seems to have been ‘recreated’ in hardware only once before now.

Outside & In

Other than being only 2U high, compared with the CL‑1B’s 3U, the WA‑1B’s front panel is almost identical to that of its inspiration, being blue with white lettering and featuring the same comprehensive set of compressor controls, metering and layout, though it does add the convenience of front‑panel meter calibration adjustment.

The CL‑1B was an upgrade of the 1987 CL‑1A, moving from hand‑wired to PCB internal construction, and the CL‑1A was based on what at that time was the discontinued UREI/Teletronix LA‑2A valve‑amplified optical compressor (it had originally been available from 1962‑1969). Lydkraft had added a full set of conventional compressor controls (attack, release, ratio, threshold and make‑up gain), plus bypass and attack/release timing selector switches — this innovative switched circuit determines whether the attack/release timings are fixed, manually controlled or determined by a combination of those two modes, delivering a fixed attack time and a programme‑dependent release. An additional innovation was the two switch‑selectable side‑chain busses that allowed multiple units to be linked and controlled when required.

The WA‑1B’s five front‑panel rotary compressor controls are 41‑position detented potentiometers that have a reassuringly solid precision under the fingers. Its trio of three selector switches (attack/release timing, side‑chain bus and meter source) have a similar sense of solidity that bodes well for their longevity, while the (not detented) meter calibration control is perhaps the silkiest and most precise rotary potentiometer I’ve handled this year, and made aligning the VU meter a simple pleasure. The unit’s bypass and on/off switches are rather chunky, all‑metal affairs that again exude an air of quality, although the mains switch could, I think, have been set back further in the front panel than on the review unit.

The WA‑1B’s rear panel carries a fused IEC mains socket, a 115V/230V voltage selector, twin TRS jack sockets for the side‑chain busses, and the transformer‑balanced XLR and TRS audio I/O connectors.

The WA‑1B offers both XLR and TRS jack I/O, as well as side‑chain link busses, which allow multiple units to share the same control signal.The WA‑1B offers both XLR and TRS jack I/O, as well as side‑chain link busses, which allow multiple units to share the same control signal.

The WA‑1B’s internal construction is of the high quality I’ve come to expect from Warm in recent years, with its through‑hole components being impeccably hand‑wired. A toroidal transformer supplies 15V power to a main PCB that houses the audio and compressor circuits together with a separate 270V supply for the valves. A single daughterboard that sits vertically behind the front panel carries the compressor control knobs. The main PCB’s largest features are the custom, large‑core Lundahl LL7908 and LL1970 transformers that, respectively, balance the unit’s fully floating audio input and output. Almost as prominent as these are the twin‑triode ECC83 (12AX7) valve, one half of which acts as the preamplifier for its other half, which forms the phase splitter feeding the ECC82 (12AU7) twin‑triode, push‑pull output stage that drives the output transformer.

Another prominent main PCB feature is the optical attenuator, the Gain Reduction Element (GRE). Unlike the majority of modern optical compressors, in which an optical element such as a light‑dependent resistor (LDR) forms part of the side‑chain that controls a VCA‑based gain cell, in the original LA‑2A (and its more accurate clones and derivatives) the optical attenuator forms part of the audio signal path. In this configuration, the compressor’s side‑chain control voltage acts directly on the optical attenuator to create the required amount of compression, and the output of the attenuator routes to the preamp half of the ECC83 via the 0 to +30 dBu make‑up gain stage. It’s worth noting that in the WA‑1B the audio signal travels along a minimalist, non‑silicon pathway that no doubt helps to deliver the WA‑1B’s 5Hz‑25kHz (‑3dB) frequency response and its ‑75dBu self‑noise at 30dB make‑up gain.


Since the WA‑1B doesn’t possess an input gain control, you’ll be using the output gain of the previous stage in your recording chain to set the level of the input signal and balancing that with any desire for, or hatred of, input‑transformer‑related harmonic distortion. With compression active, the make‑up gain control at the 0dBU point of its off (minus infinity) to +30dBU range, and the threshold control set in its off position so that no compression was taking place, the WA‑1B delivered unity gain, measured from input to output. Bypassing the compressor resulted in a metered ‑10dBVU drop in signal level.

The WA‑1B’s attack and release controls are both continuously variable between Fast (fully anti‑clockwise) and Slow (fully clockwise) times. Although Warm Audio have not released attack and release times, assuming that the WA‑1B is a faithful recreation of the original (as I believe that we can from those specifications that have been published) it is probable that these times, which can be switched between three separate circuits, are 1ms attack and 50ms release in Fixed mode; continuously variable 0.5 to 300 ms attack and 0.05 to 10 second release in Manual mode; and a programme‑dependent timing in the combination Fixed/Manual mode, in which a fixed fast attack and release time for short transients is followed by a longer, continuously variable release time (set by the release control) for longer peaks. The start of this second, longer release time can be delayed by turning the attack control clockwise, opening up the possibility of creating a more nuanced release time profile. Completing the picture, the compressor threshold control (which sets the signal level at which compression begins) has a continuously variable range from off (no compression) to ‑40dBU, and its compression ratio is, likewise, continuously variable between 2:1 and 10:1, the latter effectively being limiting.

The WA‑1B is what I’d call a ‘forgiving’ compressor — one that’s essentially incapable of delivering a bad performance.

In Use

Overall, the WA‑1B is what I’d call a ‘forgiving’ compressor — one that’s essentially incapable of delivering a bad performance on vocals, acoustic and electric guitars and basses, keyboards or synths, even at stupidly high levels of compression on highly dynamic tracks. Although it wouldn’t necessarily be my first choice on a drum kit, the WA‑1B delivered the goods on both kick drums and room mics. It is also a compressor that can be operated entirely intuitively... which is just as well, given that there’s no way of knowing precisely where you are on the attack, release or ratio controls.

Although its valves and transformers do add a touch of vintage analogue warmth, the WA‑1B possesses a speed and clarity that can also add a more modern edge to its performance. The Fixed timing mode delivers a very effective, general‑purpose performance that can serve as a useful starting point for further refinement, if that’s how you like to work. The Manual mode is an intuitive delight, especially if you like delving into the details of compression, and I really got into the Fixed/Manual mode — having the (new to me) ability to delay the onset of what I began to think of conceptually as the ‘second phase’ of release really did offer precise and more creative control of the release envelope.

The one feature of the WA‑1B that I couldn’t actually find a use for was the twin side‑chain link busses. I can’t think of a recording situation that I’ve ever been in where I would have needed to chain multiples of mono compressors together. Personally speaking, I would have much preferred Warm Audio to have added side‑chain high‑pass filtering and a normal stereo link, rather than recreating what is, to me, a rather arcane aspect of the original.

It’s very easy to see why Warm Audio “are very excited to bring the sound of an unattainable studio compressor at a ridiculously affordable price”, to quote the introduction in the owner’s manual. Really, I’d have liked to see the company take things a step further, and embrace the opportunity to differentiate this recreation from the original by adding in more of the functionality that’s expected in a compressor today. But having said that, there is no doubt at all in my mind that the WA‑1B is an extremely capable, great‑sounding, high‑quality, valve‑based optical compressor, and one that performs particularly well on vocals, both male and female. Given both its level of overall performance and the value for money on offer (it’s not an impulse purchase but far more affordable than its inspiration), then if you’re in the market for a specialist vocal compressor that could also be successfully deployed on virtually any other highly dynamic source, the WA‑1B should definitely be on your RADAR.


Other than its muse, the Tube‑Tech CL‑1B, the only hardware alternative to the WA‑1B I’m aware of is Heritage Audio’s Tubesessor, but while this offers everything that the WA‑1B does plus a comprehensive side‑chain filter, valve saturation and a stereo link facility, you pay considerably more for that!


  • Delivers the high level of overall performance you’d expect of a valve‑based optical compressor of this type.
  • Excels, in particular, at compressing both male and female vocals.
  • Very attractively priced for the performance on offer.


  • A side‑chain filter would be nice!


An extremely capable, great‑sounding, high‑quality valve‑based optical compressor that delivers a superb overall performance – especially on vocals — at a very attractive price.


£1159 including VAT.