The original Blackmer core, the Allison/Valley class A derivative, and the core with log error cancellation
<a href="//commons.wikimedia.org/w/index.php?title=User:Retired_electrician&amp;action=edit&amp;redlink=1" class="new" title="User:Retired electrician (page does not exist)">Retired electrician</a>
<span class="int-own-work" lang="en">Own work</span>. For the discussion of each circuit, see the excellent review by Ben Duncan in Studio Sound, July 1989 and the article by Gary Herbert at <a rel="nofollow" class="external free" href="http://www.thatcorp.com/datashts/AES4055_An_Improved_Monolithic_VCA.pdf">http://www.thatcorp.com/datashts/AES4055_An_Improved_Monolithic_VCA.pdf</a>