Monday, August 26th, 2019

Review of the Warm Audio WA76 FET Compressor

By editorOctober 7, 2017


Back in 2015, I spent some time reviewing the Universal Audio 1176LN FET based compressor which I had a lot of fun with and opened up my eyes to the world of creative uses of compression.  You can read that review here.

Fast forward to 2017 and I had been keeping an eye on the Warm Audio WA76 which is very closely based on the same design right down to the front panel layout.  The only reason I had held back buying a pair of these was lack of stereo linking, which I thought at the time would be necessary for my intended use across my stereo drum buss.

Then I discovered that UK distributors, Nova Distribution, had added the option of stereo linking via a small additional circuit board inside the unit and a 3.5mm stereo link jack.  That put me across the buying threshold and a pair of WA76’s arrived a few days later.  (Stereo Link version is also available in the US from my old friend Warren at ZenPro Audio).

In case you are new to the 1176 design, I’ll spend a few moments bringing you up to date.  The WA76 (like the 1176 original) uses a Field Effect Transistor (FET) as the gain reduction element within the design.  American designer and then studio owner Bill Putnam launched the original 1176 back in 1968 at a time when the wider availability of solid state transistors offered a cost and space effective alternative to vacuum tubes within audio equipment.

What sets this particular design apart from most hardware compressor on the market today is the range of compression effects possible due to the very fast attack time of 20us.  To put that attack time in perspective, it is 500 times faster than the attack time of Warm Audio’s WA-2A opto based compressor.

The 2RU x 19” rack mount unit follows the layout of the original design very closely and uses an all steel chassis which is robust.  However unlike the original 1176 design, the WA76 makes use of an external brick PSU which transforms mains supply into the 24VAC used to power the circuitry.  I’m no great lover of external PSUs but I have to say it has the huge advantage of completely eliminating hum from the WA76’s audio path.  Back in 2015 when I reviewed the original 1176 design, hum levels were a concern.

Standard WA76 rear panel

Audio input and output are transformer balanced using CineMags which provide good signal level handling and sound just right within this design.  Both XLR and ¼” jack connectors are provided which is flexible and good design practice.

Incoming audio is passed through an input attenuator which controls both the input level into the unit and effectively the amount of compression as the WA76 has non user adjustable threshold.  However it’s worth noting that the threshold is actually varied depending upon the ratio selected (so you can avoid large level jumps when you switch ratios).

Attack and release times are set by rotary control.  Attack is always fast (the slowest setting is 0.8ms and the release time can be set to between 50ms and 1sec.  In practice the release time is programme dependant so that recovery from short periods of compression is faster than from sustained compression (for any release setting).  In practice this works very well.

Post compression make up gain is also provided by rotary control with a massive 50dB available.

Compression ratios are all pretty aggressive with the lowest available being 4:1 rising through 8:1, 12:1 and a closer to limit 20:1, selected by mechanically interlocking pushbuttons.  This is not (on the whole) a subtle compressor but don’t let that suggest any lack of flexibility.  The ‘all button’ mode is also provided which requires some practice and involves defeating the mechanical interlock so that all buttons are pressed in at the same time.  This takes the WA76 into whole new compression territory and turns it into a real tone machine!  Not for the faint hearted but great when you need to make an audio statement.

A large illuminate VU meter can be switched to read either gain reduction or output level (ref to +4dBm or +8dBm) again selectable by mechanically interlocked pushbuttons with a fourth button acting as the unit’s on/off switch.

The rear of the unit houses the XLR’s and ¼” jacks, the 24VAC power socket and a small screwdriver adjust for the VUs zero gain point.  There is also a pushbutton which brings a 23dB input attenuator into the input stage.  I didn’t find this necessary to use in my fairly standard set-up.


Rear panel with stereo link mod

In the case of the ‘Nova’ stereo linking mod, you get an additional unlabelled switch (Nova’s unit on their website has labelling!) to bring the stereo linking circuit into play when the units are connected via the supplied 3.5mm linking cable and an additional knob to calibrate gain reduction between the two units (when used in stereo mode).  Switch downwards and you are in dual mono use.  Switch upwards and you are in stereo linked mode.  This stereo linking is done using additional active circuitry which derives a mono mix of the two unit’s audio input which forms the feed to the side-chain of each unit, so in theory at least, stereo matching should be excellent.  In practice I found it very difficult to keep the units matched and as the calibrate knob is at the rear of the unit (and in my case not very accessible), I eventually gave up and used both units in mono mode even though my main application is across the stereo drum buss.  In practice I found it worked fine with no real issues of stereo image shift during compression.

So what does it sound like?

Firstly across my stereo drum buss, I can hugely impact on the ‘size’ of the drum kit by bringing the WA76 into play.  Set with fairly fast attack and release settings (‘17’ is my favourite setting for both) and a ratio of either 8:1 or 12:1, drum kits can really be brought to life.  This compressor is particularly good at dealing with puny kick or snare drums which, with a combination of the WA76 and some EQ, can be made as beefy as is desired.  The WA76 also provides that important ‘glue’ which hugely simplifies balancing the various drum sources within the drum mix.

I use my own pair of WA76s as the first element within my stereo drum buss insert, followed by an elysia xfilter stereo EQ and then finally an IGS S-Type Stereo Compressor with the IGS used into heavy compression but in parallel mix mode and set 75% to clean.  This is a monster chain and gives me a lot of control over the stereo drum mix.  I will usually route electric bass into the same buss so that the whole rhythm section is ‘in tune’.

What surprises you about the WA76 is just what a good general workhorse it is across a wide range of sources.  It can be amazing used with vocals, especially when you want to bring the vocalist forward in a busy mix and in this regard it is more effective than using EQ to try and do the same job (but both is also good!)  It is always good with bass guitar and can be a very effective compressor (and tone control) across acoustic guitar.  You do need to keep your wits about you; this compressor is capable of very aggressive effects, so you need to work the controls and find the sweet spot.  I would never class the WA76 as a transparent compressor but when you need to find some attitude and some glue then it usually does the business.

You can use it across the two-buss but again bear in mind it’s a minimum 4:1 ratio so you might decide to use it as a parallel compressor with just a small amount mixed with the ‘clean’ buss.

The WA76 is well put together with quality pcb’s and zero hum in the audio path.  Warm Audio have done a great job of offering this classic FET compressor at a very affordable price.  If you are looking to move on from 1176 soft based emulations to the real thing, then the WA76 is a great buy.

Robert Campbell
October 2017

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