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Undertone Audio UTEQ500

500-series Equaliser By Matt Houghton
Published April 2024

With a chameleon‑like ability to replicate the curves of almost any analogue bell or shelf EQ, this has to be one of the most versatile equalisers out there.

Undertone Audio UTEQ500The UTEQ500 is a three‑band EQ, and yes, I know you’ve all used those before — but not one like this. Because, despite having only six dual‑concentric knobs and a few toggle switches to play with, the UTEQ500 is probably the most versatile ‘console‑style’ analogue equaliser I’ve ever had the pleasure of testing. A solid‑state design from UnderTone Audio, this single‑slot 500‑series module is electronically balanced, and the filtering is performed using resistor‑capacitor networks. With no transformers or inductors at play, it won’t surprise you to learn that it doesn’t sound ‘vintage’ in terms of harmonics and saturation. Rather, it’s all about the curves and the way you can manipulate them, though there is still definitely a sweet spot into which you can drive it for a little ‘crunchy’ attitude if you like to do that.


All three EQ bands are identical, other than that they operate in different frequency ranges. The frequency is determined using a pot rather than switches, so you can set each band freely within its range. Each band can also be engaged/bypassed independently. The high band, at the top of the module, runs from 1.4 to 22 kHz; the mid band controls are switchable to operate in either a low‑mid (90Hz to 1.4 kHz) or high‑mid (390Hz to 6kHz) range; and the low band frequency control covers 20‑340 Hz. There are also small toggle switches that allow you to set each band to boost, cut or notch — more on that below.

All of the six knobs are dual‑concentric types. That’s a good call on a 500‑series module because, as on a console, panel real estate is a precious commodity, and this choice permits lots of functionality to be accommodated while still allowing access for large fingers and thumbs. Of course, it also means that there’s more going on here than first impressions might suggest, and if you’re one of those who likes to dive in without reading up on what the controls do, you might like to approach this particular EQ differently.

The outer knob on the left of each band is its gain control. This is marked from 0‑10 rather than in dB, presumably so that the legend is uncluttered and relates meaningfully to the inner knob as well as the outer one. The gain pot can be set anywhere from 0‑15 dB, so with the boost/cut switch, the total range is ±15dB. When in notch mode, though, it can go deeper still, as I’ll discuss below. The outer knob of each band’s control on the right is the frequency selector. Then we have the inner controls, with the blue‑capped one on the right being a Q (bandwidth) control and the black‑capped knob one a Shape control.

At its fully anticlockwise position, the blue Q control gives you its widest bandwidth, with a Q of 0.3 delivering generously wide, gentle curves. At the opposite extreme you get what, for analogue hardware, is a very surgical Q of around 10. So with just the two outer controls and the blue inner one, you already...

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