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The Hidden Dangers Of Vintage EQ

Pultec EQP‑1A & Models By Hans Weekhout
Published June 2020

The original and best? EQP‑1A equalisers are once again being made under the Pulse Techniques brand.The original and best? EQP‑1A equalisers are once again being made under the Pulse Techniques brand.

Plug‑in models of classic hardware can sound great if you feed them the right level. But what level is right?

Like the real thing, plug‑in models of the famous Pultec EQP‑1A can add a unique character to your mixes. The silky high band polishes the top end in a way that's nothing like the sound of your DAW's built-in EQ. A little bit of low boost causes kick drum and bass to really be felt, rather than just heard.

If you're like me, though, you may have found that certain Pultec plug‑ins sometimes don't sound right. It turns out that there is a reason for this — and it's down to the way different plug‑ins respond to input level. Some plug‑ins need to be hit hard in order to bring out their mojo, while feeding the same level to others causes extreme distortion!

Am I Hot Or Not?

In a hardware Pultec, valves, transformers and other electronic components all contribute distortion, which shows up in the output as newly created overtones. By adjusting the input level of a vintage unit, you can determine the exact amount of coloration.

The same is true of most Pultec plug‑ins — but the vast majority of them do not have an input gain control. This means that the amount of coloration is determined simply by the level coming into the plug‑in. If that signal is too hot, too many overtones will be generated. Distortion will cause the mids and highs to sound harsh, and the low frequencies of kick and bass will be augmented by unwanted lower-mid harmonics. This will add a 'gargling' quality to the music, causing those instruments to shrink in size. Not something to look forward to!

So, the key to getting the best from Pultec plug‑ins is to manage the level going into them. And this is where the problem arises, because it turns out that different Pultec plug‑ins respond very differently to input level. Many of them produce distortion that varies proportionally with input level, but in others, there's a threshold above which distortion dramatically increases. And that's not all: some of them, quite unexpectedly, produce less distortion with hotter signals, and some introduce no distortion at all!

Six Of The Best

For my tests, I analysed some of the most popular Pultec-inspired plug‑ins: Waves' PuigTec EQP‑1A, Universal Audio's Pultec EQP‑1A and EQP‑1A Legacy, Softube's Tube‑Tech PE-1C, the Vintage EQ in Apple's Logic Pro and Analog Obsession's free Rare, along with UA's recreation of the more modern Manley Massive Passive.

Testing was done in Logic 10.4.8 at a sample rate of 44.1kHz. Each plug‑in was fed a pure 100Hz sine wave at various levels. The output spectrum...

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Published June 2020