• Sterling Skye

1 Doesn't Mean 1. Know Your Gear: Pultec EQP-1A


The Pultec EQP-1A equalizer. A thing of beauty with unparalleled sonic characteristics. An updated model created from the original EQP-1 invented in 1951 by Eugene Shenk and Ollie Summerland of Pulse Techniques (Pultec). This incredible piece of gear has found its way into nearly every recording and mixing engineer's tool kit. But, there are some secrets hidden within it's circuitry that you may not be familiar with.


In this article, I'll be referencing to Universal Audio's plug-in emulation of the EQP-1A. This is the version I use in my mixes. All other variations/emulations of the EQP-1A should have similar specifications. Always refer to the operating manual of the Pultec model you're using for exact specifications.


The EQP-1A is described as a 3-band, tube amplified program equalizer. The layout of this unit is not as straightforward as it may look. Even I was fooled by the controls when I first started using this EQ. Looking at the controls, you can see there's a low frequency and high frequency section. But, where's the third band? This is where we have to open the manual and shed some light on the inner functions of this unit.


The below image displays the 3 separate bands and their associated controls.

I'll be the first to admit that this is not how I predicted this unit operated. I never even acknowledged the "ATTEN SEL" dial until I read the operating manual. This might be a big aha! moment for some of you, just like it was for me. So now that we have distinguished the 3 EQ bands, let's dive deeper into the numbers behind the knobs.


Let's start with the low frequency band. There are 3 controls in this band that adjust an extremely broad low frequency shelf. So broad, in fact, that a boost at 30Hz/CPS (cycles per second) affects frequencies up to 1000Hz!


Boost: 0 to +13.5 dB.

Attenuate: 0 to -17.5 dB.


Looking at the above specifications, it's starting to make sense when I claimed how 1 doesn't mean 1. If the boost dial is set to 10, that equates to 13.5 dB of gain. This puts a setting of 1 somewhere around 1.35 dB. Same concepts goes for the attenuate dial. If the dial is set to 10, that equates to 17.5 dB of gain reduction. This puts a setting of 1 around -1.75 dB.

The next band also has 3 control dials. A similar stepped frequency selector, this time in KCS (kilocycles per second), and a variable boost dial. The 3rd dial is a variable bandwidth dial. This dial only affects the selected frequency band in this section. Keep in mind that sharp does not mean surgical sharp. A sharp bandwidth on this unit is still fairly broad if you compare to a sharp Q on a digital counterpart.


Boost: 0 to +18 dB.


To continue my 1 doesn't mean 1 argument; setting the boost dial to 10 equates to 18 dB of gain. This puts a setting of 1 to around +1.8 dB.

The final band is a high frequency shelf with 2 controls. A stepped frequency selector and a variable attenuate dial. Similar to the low frequency shelf, this high frequency shelf is extremely broad. Attenuating at 10kHz affects frequencies down to 1000Hz and lower!


Attenuate: 0 to -16 dB.


A full frequency response chart from the original manual can be found HERE.


One last hidden element to be aware of is the small bump in gain added by simply implementing this EQ into your signal chain. Detailed examinations of the original hardware version of this unit showed an apparent 1.13 dB level boost. This boost has been added into most plug-in models as well. Although this may not be a significant boost in signal level, it can add to the "louder is better" argument. I wouldn't make it a common practice to reduce the output by 1 dB, but if you're looking for a more accurate way to analyze the "color" being added to a signal, a 1 dB reduction could do the trick.


Final Thoughts:


I would highly recommend checking out the Pultec EQ Shootout article by Lynn Fuston. You'll find in depth comparisons of different Pultec-style hardware and software units with audio samples. You can find the article HERE.


The Pultec EQP-1A is an incredible piece of equipment. I can guarantee that at least one instance of this EQ can be found in all my mixes. It sounds incredible and it's extremely musical when boosting frequencies. I especially love it on drums, bass and vocals. Hopefully I can get my hands on a hardware model in the future.

If you learned something new o