500 series Equalisers

500 series modules

It had to happen.

One day, as one of the few manufacturers of consoles with 500 series support,
we simply had to design 500 modules. This day has come.

We’re proud to introduce the first of our 500 series modules.
More modules are in the works and will be released over the coming months.


4-band Inductive Equaliser


The name Iridium is based on “Iris”, the Greek goddess of the rainbow.
And that is exactly what you’ll get. A silky smooth rainbow of EQ.
Dial in any frequency, and be amazed.
We have yet to come across anyone who does not like this EQ.

Inductor based circuits are the “holy grail” of equaliser designs.
These were used for example in the much favoured Pultec equaliser design, which dates back to the late 1950’s.
Owing to their unique electro-mechanical properties, inductors impart a character all of their own, which is very distinctive.

The Iridium uses 16 inductors spread out over the four bands, with custom-wound Carnhill inductors in the low-mid and low bands, giving precise control and the inductor sound on each band.

Iridium is a Class-A, discrete design, with all components carefully chosen and matched to provide an extremely musical sound. You’ll get a very distinctive sound, which most sound engineers love.
However, this circuit is a decidedly modern design with updated techniques and components that were simply not available 60 years ago. This is definitely not a “clone” or “copy” (we at Interphase Audio do not build clones or copies of anything)

As a consequence of using inductors, this provides a “peaking” or “bell” characteristic, giving tight control of the frequency selected.

Each band provides switch selection of any of 6 carefully selected frequencies chosen at musically pleasing intervals.
Each band allows very fine control of up to 15dB cut or boost per band.

Iridium is available as 500 series module or as 51x series module.
To find out more about the difference between 500 and 51x modules, check our
500 page

Our rackmount
NDUCR features two Iridium running at +/- 24 volts.

Iridium 360 Degree

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Iridium Specifications

• Input impedance: 30kohm
• Common mode rejection: 80dB
• Distortion: 0.001% (+4dBu output, 1kHz)
• Frequency response: 7Hz to 70kHz (-3dB)
• Boost / Cut range: +/-15dB (continuously variable)
• HF Frequency: 8, 9, 10, 12, 14, 16 kHz (stepped)
• HMF Frequency: 1.5, 3, 5 6, 7, 8 kHz (stepped)
• LMF Frequency: 125, 250, 500, 1k, 2k, 4 kHz (stepped)
• LF Frequency: 50, 80, 100, 150, 300, 600 Hz (stepped)
• Filter Q: 1.2 (just over 1 octave)
• Maximum input level (500 module): +28dBu
• Maximum input level (51x module): +32dBu
• Maximum output level (500 module): +28dBu (10k load)
• Maximum output level (51x module): +32dBu (10k load)
• Nominal input and output level: +4dBu (electronically balanced)
• Output impedance: 100 ohm
• Noise floor (typical, unweighted, EQ on): -80dBu
• Noise floor (unweighted, EQ off): -100dBu
• I/O connections (Rack XLRs): pin 2 +, pin 3 -, pin 1 ground
• Current requirement: 65mA (maximum) per rail
• Size and weight: Standard 500 Series, 0.4 kilos

is available as 500 series module or as 51x series module.
To find out more about the difference between 500 and 51x modules, check our
500 page

To order, go to our
Purchase page


What are Inductors ?

Inductors are wires wound around a coil that provide a form of frequency-dependant resistance. When they saturate, they bring out beautifully musical harmonics that give your tracks the silky-smooth, polished sound that has made classic consoles and equipment so desirable for over sixty years. This is what makes them different from capacitor-based EQ designs, which do a great job at surgical equalisation. But it has always been up to Inductors to provide the tone.

While some of the inductors we use are off-the-shelf, we have choosen to also use custom inductors. This attention to detail in controlling variables such as the winding and core materials in relation to the surrounding circuitry allows our Inductive EQ’s to capture the classic sound, while at the same time be up to todays standards in sound-quality and noise level.


I received the Iridiums and have been trying them out for almost two weeks. They sound amazing. Really, really great sound. I'm so impressed with how easily they can energize a sound without sounding like anything drastic was done to it. Of course the top and bottom end boosts sound great, but one thing that surprised me is that midrange cuts seem to sound particularly good with this EQ. I don't know what it is--maybe I'm imagining it! But I feel like I can tame whatever is honking in the mids and everything still sounds nice, and not like I just killed the presence of the sound.

Thank you for a really great EQ! I will be keeping an eye on your future designs.

Phil, Chicago, March 2022

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