In recent years more and more audio equipment manufacturers have tried their hand at creating an 1176 style FET compressor. There has also been quite a raise in popularity within the DIY scene to build different 1176 revisions to the same specifications as the originals. Most recently Warm Audio have produced a Rev-D clone with CineMag transformers, entering the market at an affordable price point of around £530. A modern Universal Audio 1176 will set you back around £1530. This blog post will have a quick look at the technical differences in gain reduction curve and distortion, between a modern WA76 and an original Urei 117LN.
This first graph shows a clean sine sweep, and then the same sweep routed through the WA-76. When the same test was performed on the Urei noticeable harmonics could be seen, whereas the WA-76 only presents what seems to be a higher noise floor in the high frequencies. Both tests were carried out without gain reduction present.
Proceeding from the results gathered from the first graph, I looked into the distortion created from gain reduction, instead of just from the idle transformers. The Urei can be seen to produce an evenly decaying harmonic series throughout even and odd harmonics. The WA-76 however has much stronger odd order harmonics, over three times as loud as the Urei. The phase response at each harmonic is drastically changed with the WA-76 also.
The following two gain reduction curve graphs show the difference between the two 1176 models. The first the WA-76 and the second the Urei 1176LN. Immediately it is visible that the Warm Audio had a much smoother curve to its release, whereas the Urei seems to push back with an ‘S’ shape curve.