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Smooth, vintage-sounding induction coil EQ

By Phil O'Keefe

 

When it comes to EQ, the type that most people are probably most familiar with is the parametric EQ, and its cousin, the semi-parametric EQ. These generally have a boost / cut knob for each band, as well as a knob for selecting the center frequency that will be boosted or cut, and in the case of a true parametric design, a Q or bandwidth knob. However while they're very common today, parametric EQs are not the only EQ type available, and their large number of knobs makes them less than ideally suited to the very popular but front panel real estate-challenged 500-series rack format. Prior to the introduction of parametric equalizers in the early 1970s, other EQ designs were far more common. Many of these earlier equalizer designs have simpler controls, with switches for selecting pre-set frequencies, and knobs that allow the user to cut, and sometimes to boost at the selected frequency. This is an approach that is common with vintage equalizer designs, such as the much-loved vintage Neve and Pultec equalizers.

Induction coil based equalizer circuits like the ones used in vintage Pultecs are in some ways less adjustable than the filters commonly found in a modern parametric equalizers, but they are well-loved for their smooth, musical sound. While they're generally not the first-call units for narrow bandwidth surgical EQ duties, their sonic characteristics make them a great choice for sweetening and more broadband tonal adjustments. Think color and character as opposed to clinical and precise. The Radial Engineering Q3 is an induction-based EQ that uses both passive and active EQ circuity in its design and a unique preset-based approach. While the controls function a bit differently than what many people will be familiar with, there's a lot of useful sound-shaping capabilities hidden away within this 500-series unit, and they're surprisingly easy to access.


What You Need To Know

  • Like a vintage Pultec, the Radial Q3 is a induction coil type EQ, but while it is based on vintage designs, it isn't a clone of any previous equalizer.  
  • The Q3 is intended to be housed in a 500 series rack, with the rack supplying the power and the physical I/O connectors. I tested the review unit in a Radial Engineering SixPack rack, and it mounted into it easily, and worked perfectly, without any problems.
  • The current draw of the Q3 is a very reasonable 25mA, so even if you're using it with a power-hungry 500 series tube preamp, it's not likely to strain your host rack's power supply.
  • When used with a Radial Engineering 500 series rack or other unit that supports Omniport functions, the Omniport jack provides you with unbalanced I/O on a 1/4" TRS connection, with input on the tip, and output on the ring. This makes it very easy to use the Q3 as an insert on mixing boards with unbalanced 1/4" TRS insert jacks.
  • The main I/O is balanced, and designed to work with nominal +4dBu line level signals.
  • There are four knobs on the Q3's front panel. The three EQ knobs are labeled Bass Mid and High. Each knob is actually a twelve position rotary switch, with 11 preset EQ curves plus an Off setting. The manual contains detailed information about what each numbered preset for each band does. The High and Bass band presets are primarily boosts, while the Mid band presets are comprised primarily of subtractive EQ cuts.
  • The fourth knob is labeled Gain, and gives you the ability to compensate for any level increases or losses caused by the boosts and cuts from the EQ circuits. The range of the control is sufficient to maintain unity gain through the unit, even with some rather dramatic EQ dialed up. Because the Gain circuit is located before the EQ filters in the signal path, it's possible to run hot signals into the Q3 and then boost the levels going into the filters significantly more with the Gain knob and cause the inductor coils to saturate, which can add even more character to a sound.
  • The High, Mid and Bass knobs each have a corresponding "Shift" toggle switch. The Shift switch affects how much boost or cut you get with each preset you select. When the Shift switch is clicked to the right, the effect is about half as pronounced as when it's clicked to the left. This is quite handy - I found as I was auditioning various presets that if I found one that I liked, but that I thought was "a bit much", I could cut it back and usually make it "just right" or at least much closer to it with the Shift switch.
  • A 100Hz High pass filter is also provided, and when used in conjunction with the Bass Boost presets, it provides yet another tool for shaping the low end.  
  • Between the 11 presets on each of the three bands, plus the two possible Shift toggle switch settings per preset, there are over 12,000 possible EQ curve combinations with the Q3. While not all of them will be suitable for every sound source, you're bound to find something useful for practically any type of sound.  
  • An EQ In switch and green LED let you know when the EQ is active, and allows you to bypass the EQ filters (the Gain knob remains active) to compare the EQ'ed signal and the unprocessed signal.
  • Dialing up a suitable EQ sound is fast and easy. Because the EQ is preset and uses switches instead of continuously variable controls, it's also easy to return precisely to your favorite settings.
 

Limitations

  • The Q3 is a tone-coloring and tone-shaping tool, but not a surgical EQ. If you need the kind of precision control that you get from a full-parametric EQ in order to fix a narrow-band problem frequency, then this obviously isn't the ideal EQ for the job… but when you want to add vibe, color, and enhance and shape the tone of a sound source, the Q3 is an excellent choice.
  • Similarly, the preset-oriented design of the Q3 doesn't lend itself quite as well to mix bus duties as it does to processing individual tracks when recording and mixing.
  • The Shift switches are a bit tricky to reach and activate - a fact that Radial points out in the Q3's manual. They suggest using a "pen or tweaker" to adjust the switch settings. I found I could also use my fingernail fairly easily, but if you have larger hands, you may need to keep a suitable tool nearby.
  • Some clicks and pops when changing settings on the EQ switches is normal and is to be expected with a passive / coil based EQ. Again, Radial warns users about this in the Q3's manual.
 

Conclusions

This is a really fun, fast and very straightforward EQ to use, and it's super-easy to call up some very cool sounds with it. While the manual gives you the lowdown on what all the various preset EQ curves are, most people are going to forget about trying to memorize them all, give in to the interface's charms, and just click the knobs and combine the various presets on each band until they hear something they like - and that's exactly what they should do. It's all about listening to what this very smooth and musical EQ is doing and picking what sounds most appropriate for the situation at hand, and the design of this unit encourages that approach.

The Radial Engineering Q3 is the type of EQ that is at its best when adding character, color and excitement to the sound. It really isn't a good alternative to a surgical EQ when the situation calls for that, but it is a terrific tonal shaper. You can add considerable boost in the highs, but they still remain smooth and sweet sounding, without a trace of harshness. The bass boosts are similarly impressive; adding both weight and substance without getting muddy and losing definition and detail. The ability to cut mids is also a powerful feature, and adds even more tonal shaping capability to this fun-filled box… and things really start getting interesting when you combine more than one band to create different combination EQ curves and start slamming levels a bit to get some saturation happening. Of course, any preset-based unit is going to live or die based on the usefulness of the presets that are included, and the Q3 does very well in that respect - the presets are flattering and well-suited for a variety of sound sources, and the Shift switches increase the options even further. From vocals to acoustic and electric guitars, bass to drums, the Q3 is an equalizer that can bring a bit of magic to your tracks with its warm, silky, vintage-inspired sound, and compared to what most other modern and vintage inductor-based equalizers cost, it's a bargain. The Radial Q3 is filled with the kind of character and personality that you just won't hear from most parametric equalizers - whether they be hardware units or plugins. It is a sound that I find very appealing. Check one out if you get a chance and see if you agree.  

Resources

Radial Engineering Q3 500 Series Induction Coil Equalizer ($800 MSRP, $699.99 "street")

Radial Engineering's Q3 product web page


Specifications

Circuit type: Coil / Capacitor / Resistive Boost and Cut filters
Frequency Response: 20Hz-20kHz, +/- 1dB in non EQ positions
Dynamic Range:  >112 dB
Noise: <-90dBu (600 ohm source impedance - filters off)
Noise: <-87dBu (600 ohm source impedance - filters on)
Output Headroom: +27 dBu
Clip Level - Input: >+20dBu
Clip Level - Output: +27dBu
Equivalent Input Noise: -100dBu
THD+N: <0.003% (0dBu input at 1kHz)
Input Impedance: 12k balanced
Output Impedance: 440 ohms balanced
Warranty: Three years, transferable



Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.  



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