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Pulse Techniques EQP-1A

Analogue Passive Equaliser
Published February 2019
By Hugh Robjohns

Pulse Techniques EQP-1A

Is this, as the manufacturers claim, the most authentic recreation of the venerable PulTec EQP‑1A?

As a standard facility of most mixing consoles and DAWs, we all tend to take EQ for granted, even though there are many different types of equaliser with varying levels of sophistication and application. While the true origins of the first audio equaliser are shrouded in the mists of time, two names stand out for me as pioneers of audio equalisation: Peter Baxandall from the UK, and the American, Eugene Shenk. Baxandall was an electronics engineer (and friend of our esteemed Editor In Chief) who came up with a very elegant circuit for an active bass and treble equaliser. He published his design, royalty-free, in 1952 and it has subsequently been employed almost universally in mixing consoles and hi-fi amplifiers, bearing his name as the Baxandall equaliser or 'tone control'. Amazingly, at around the same time in America, Gene Shenk developed a passive design which has become the legendary studio equaliser — the PulTec EQP-1.

The PulTec name is an abbreviation of Pulse Techniques Inc, the full name of the company Shenk established with his business partner Ollie Summerlin at the start of the 1950s. Both Shenk and Summerlin (or Summerland, as many articles claim) were skilled electronics engineers, Shenk having spent 14 years working at RCA on radio telegraphy, while Summerlin had worked as an engineer for Capitol Records and later sold Ampex tape recorders, so brought a good knowledge of the flourishing recording studio industry.

Initially, PulTec made things like adjustable power supplies for valve equipment and audio oscillators, but one of Summerlin's former colleagues at Capitol had moved to MGM to build a mastering studio, and he commissioned PulTec to build a bespoke mastering equaliser. The result was the Model EQP-1 Program Equaliser, which was introduced to the wider studio industry in 1953. The EQP-1 continued to be made in one form or another for 30 years, and even though PulTec were always a relatively small-scale operation, they manufactured around 30 different products in all. Many were equalisers based on the same technology, but there were also microphones and phono preamps. Unfortunately (and amazingly, in hindsight!) when Shenk wanted to retire, he couldn't find a buyer for the business and the factory doors closed permanently in 1981.

The Rebirth of PulTec

With so many vintage audio companies the story could simply have ended there, but 20 years later another American, Dr Steve Jackson, decided he wanted to rebuild the original PulTec equaliser accurately and faithfully, with no component compromises and no gratuitous enhancements. The impetus behind this courageous decision was that because so few original EQP-1s survive without modification, models in good condition from the 1950s and '60s can attract quite ludicrous prices on the rare occasions they come up for sale. And although several manufacturers offer modern reproductions of the EQP-1, there are varying degrees of authenticity and many have also been 'enhanced', moving them even further away from the intentions of the original design.

Amongst the modern hardware recreations or homages of the EQP-1 are models from Manley, Summit Audio, Tube‑Tech, Cartec, Warm Audio, Magnetec, Drip, and various others; several of these have been reviewed in Sound On Sound over the years. For those skilled in wielding a soldering iron, there are many constructional schematics online and comprehensive DIY kits too. And of course the DAW user can employ a digital plug-in emulation from UAD or Waves, amongst many others.

However,...

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Published February 2019