Presence EQ RS127 / RS135 Style Inductor EQ Pair

Inspired by the curves of the historical and legendary equalizer, this Groupdiy project used passive inductor equalizer circuitry scaled into a form that integrates with modern impedance studio workflow.

Jensen transformer balanced line input, output to instrument / DI input for mic pre makeup gain. AML inductor. 2k7, 3k5, 8k, 10k, 10db boost / cut in 2db steps.

Many types of rare vintage and high end modern capacitors of different dilectric and type were auditioned before settling on the boost caps, which are NOS military PIO. Cut caps are high-quality polypropylene film.

You won’t get anything like this in a plugin. It’s fascinating to hear and hard to describe...instead of sounding like it’s still in flat, 2 dimensional space but brighter, the frequency area’s energy seems to lift out of the speakers.

Top knob is db boost/cut, bottom is (from ccw) 2.7k, 3.5k, 8k, 10k.

Test results may vary depending on load; my test on a 150Kohm input:

0db boost/cut response shows 1 db down @10K, 2db down @15K, 4db down at 20K.

Max boost tilts slightly downward from 9.7db to 8.5db (from 2k7 to 10k)

Max cut tilts slightly upward from -9.25db to -10.7db (from 2K7 to 10 K)

Boosts hit frequencies very close to target, cuts at 8K and 10 K are very close, 2K7 hits closer to 2K6, 3K5 hits closer to 3K4.

Some slight nicks here and there, one face has a 5 mm or so long metal scratch under the paint. Grey paint is heavy duty and dried for over a week before assembly but there is a small light smudge that won’t come out on one unit, only visible in certain light. There is some paint wear on the black chassis mounting side where the screws are visible, also small ones on other sides. I’ve tried to highlight these blemishes in the photos but some have been covered up with permanent marker. They are not visible from a few feet away. The minty green color inside the faceplate in the open chassis pics is overspray from an attempt to make these closer to traditional green, but it wasn’t strong enough paint. There are rubber feet that I have not attached (in order to make packaging more efficient) but will include.