1975 Pultec EQ

Forest Q6 Coil EQ

Close up of an inductor coil

Q3 - inside view

Fletcher-Munson Equal Loudness curves

Q3™ Development

Several years ago, we started developing our first coil EQ called the Q6. Back then, we immediately found ourselves drawn to the most revered of all designs – the induction coil equalizer. Coil EQs are renowned for the warmth they introduce into the signal path and reduced phase distortion when pushed to extremes.

Vintage coil EQs such as the Pultec are coveted today due to the way they add warmth to the signal path along with a creamy top end. This is particularly useful with today's often sterile digital recording environment. One challenge with this older design is that has a limited frequency selection. Manley's Massive Passive expanded upon the design by adding additional frequencies, more control and increasing the number of EQ bands. Another challenge is of course cost: not everyone can afford to spend $10,000 to $20,000 on an equalizer.

We took a different approach. Instead of trying to follow the 'clinical approach' of a 'parametric graphic equalizer', we chose to create an EQ that would conjure up spirits! In other words, we wanted to move away from the 'traditional' whereby one selects a frequency, adjusts the width and changes the amplitude. This type of EQ'ing is standard equipment in most digital consoles and software programs.

The original Q6 design and the 500 series Q3 are different. They employ a preset curve architecture that is completely unique. As you get familiar with how the Q3 works, you will quickly find yourself gravitating to specific tones for certain instrument and mic combinations, essentially, creating a secret sauce that can make a snare stand out, a bass solidify or an acoustic guitar shimmer.

Facing the challenges

The challenges with coil EQs are numerous. An induction coil employs an air-filled bobbin that works like a transformer. When current is applied, a magnetic field is generated. This not only causes the coil to generate a magnetic field, but also makes it prone to being affected by outside electro-magnetic forces. This problem is amplified when you try to pack the coils tightly together inside a small box.

During the development stage, we spent months trying to eliminate noise. We discovered that a shielded coil sounds very different from non-shielded one, even though both may share the exact same specifications. The shield actually collapses the magnetic field which in turn changes the tone. We tested dozens of variations until we finally made our choice. But getting the coil you want requires significant resources. You cannot simply buy 'off-the-shelf' coils to do this type of thing. Each of the coils must be custom ordered. And because mechanical switches are required in the design, particular attention must be paid to both the quality of the contacts and the mechanical attributes of the switch.

Developing the feature set

The Q3 employs 9 coils that are combined with various circuits to generate 33 different preset curves. These are separated into three groups with 11 high-frequency boost curves, 11 mid cuts and 11 low frequency boosts along with a bypass position for each band. Three custom ordered USA-made Grayhill switches are employed for the task. Grayhill is considered to be the premier switch manufacturer of compact military grade rotary switches and like all quality devices, cost a bundle. But considering the Radial Q3 will likely play a never-ending role in your studio, longevity will be critical to the performance. With Grayhill switches, you can confidently twist and dial to your heart's content without worry of failure or downtime.

For the most part, the high and low presets are set up to boost frequencies while the mid presets will cut frequencies. This is purposely done following the way humans perceive sound. Back in 1933, scientists Fletcher & Munson demonstrated that our ears are most sensitive to the mid range thus the reason we naturally gravitate towards 'smile-shaped loudness curves' when we listen to music. By accentuating the highs and lows, and cutting the mids, the Q3 enthrals and enhances our aural senses, captivating the listener with an abundance of character.

Controlling the beast

Approaching the Q3 is easy. Close your eyes and listen. Each curve has been carefully sculpted to create interesting effects. To add even more splice to the soup, three miniature toggle switches enable you to reduce the amplitude of the effect. Point being, what may flatter an acoustic guitar or add crack to a snare drum may be a over the top for a female voice or unusable on flute. Simply 'shift down' to suit.

As you become familiar with the various types of curves in each of the three bands, you will quickly begin to combine curves to create new ones. And new ones you will find... in fact, if math serves correctly, there are just over 13,800 tone combinations (24 x 24 x 24). But don't let this number scare you. The most mind boggling thing about the Q3 is the repeatability of the circuit. Our brains easily remember patterns or short numbers like padlock combinations. Once you find your favourite Fender P-bass slap tone, you will quickly memorize the dials with 8-3-6 for each of the three 12 position switches. Add or subtract to the effect by switching the mini toggle. Or take it one step further by reducing the bass content with the high-pass filter.


Three example setting for guitars.

Ultimately, the Q3 will help you discover signature tones that will make your recordings stand out. The Q3 is truly a creative tool for those that are looking to develop new sounds while adding the warmth and character of old-school vintage nirvana!