Monday, 13 May 2013


I have just completed tweaking and testing a new EQ based on the EQ used in the famous EMI REDD desks. I have duplicated the standard per channel +- 10dB range stepped bass and treble controls (both 'classic' and 'pop' versions) and also included the brilliance boost/cut control from the EMI RS127 plug-in module which provided boost/cut at frequencies of 2.7KHz, 3.5KHz and 10KHz in addition to the 4.7KHz of the 'pop' plug-in. This all fits on a small PCB just 100mm by 100mm.

The three level control switches are mounted directly onto the PCB and the brilliance frequency select switch is connected by a short length of ribbon cable. The schematic is a little more complex than some of the other EQ circuits I have designed because the RS127 appears to have the same Q in both cut and boost. This necessitates using separate inductors for brilliance boost and cut as shown in the protootype schematic below:

I am going to fit this EQ to one of the channels of the demonstrator mixer. I plan to have two channels with Sowter input transformers and Pultec EQ. As well as being suitable for recording, these two channels can also be used for mastering as they have identical transformers and EQ. The Cinemag input transformer will be paired with the Helios 69 EQ and the Jensen with the new REDD EQ. Prototype test results can be found here:

Test Graphs

I also made a short demo recording showing the REDD EQ in action on a pre-recorded track. You can hear the result here:

Just Bob

The left channel is the track with EQ applied and the right channel is me commentating on the EQ settings at each point in the track. The track was recorded by by good friend Bob Wright:

The Song Factory

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