This week my FdA Audio & Music Production students at dBs Music in Plymouth (UK) did a compressor “shoot out” as part of their Analogue Recording Methods module.

We compared the following units:

  • Neve 33609 (Diode Bridge)
  • GAP Comp-54 (Diode Bridge)
  • TL Audio C5021 (OTA)
  • Joe Meek SC2.2 (Optical)
  • Universal Audio 6176 (FET)

The first surprising result was the similarity of the diode bridge based Golden Age Projects Comp-54, based on the Neve 2254 circuit, and the Neve 33609.  The units were a lot more similar than you would expect given the massive price difference.  I still have the standard transformers in the Comp-54 as I haven’t got around to upgrading them yet.

The inside of the GAP Comp-54. Note the empty transformer slots for installing upgraded transformers. There a three transformers in this design to keep the audio differential and stabilise the diode bridge.  More about this type of circuit’s operation (in the Neve 33609) circuit can be obtained here.

The TLA 5021 is OTA (Operational Transconductance Amplifier) based, making it current, rather than voltage, controlled (like the Ross compressor or Dynacomp guitar pedals). With the valve amps in it, it was harmonically interesting and, sounded good when used aggressively.

The 1176 side of the 6176 performed as expected.  This version is based on later revisions rather than the often cloned revision D or E.  As well as upgrading my GAP Comp-54, an 1176 build is still on my list of projects to attempt, there’s lots of information out there on building a DIY version.  Although, with the release of the, very favourably priced, Warm Audio WA-76, I wonder if  upgrading a WA-76 might be a more lucrative project.

Last up was the Joe Meek SC2.2 Optical circuit.  This one surprised me the most, designed as a stereo compressor, we decided to try it across a mix.  Not expecting it to perform as well as the Audient ASP’s built in (VCA) mix compressor, we strapped it across the mix bus.  It sounded great on our mix but completely different to the VCA types.  We didn’t get to test this further as we ran out of time in the session.  However,  when we get time to repeat this, I will record some audio clips and append them to this post.

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