There’s something about a Pultec EQP-1 that enhances anything you run through it, even if you don’t apply any EQ. “In regards to the EQP-1, the term ‘magical’ seems to be appropriate. Negative feedback is derived from an extra secondary winding on the output transformer - so that transformer distortion and some output loading effects are automatically compensated. The input section is built around an ECC83 (12AX7), while the output transformer is driven by an ECC82 (12AU7). Both valves are dual triodes, the two halves of each being used in the push‑pull mode to handle each half of the balanced audio through each gain stage. In order to make up for the lost gain, the Pultec uses a simple dual‑valve amplifier stage that is, unusually, fully balanced throughout and operates in a classic push‑pull arrangement. This is a shelf-cut with up to 16 dB of attenuation.Īs we said before, many engineers have found that audio can be enhanced simply by passing the signal through the Pultec, with the EQ switched out. The high frequencies can also be cut at 5, 10 and 20 kHz. The Pultec high-frequency section features a boost-peaking EQ and offers seven centre frequencies – at 3, 4, 5, 8, 10, 12 and 16 kHz – which can be boosted by up to 18 dB, while a Bandwidth control alters the Q of the equalization curve from sharp to broad. These frequencies can be boosted to a maximum of 13.5dB and attenuated (cut) by 17.5dB. The low-frequency section of the EQP-1A is a shelving EQ, providing four selectable frequency bands at 20, 30, 60 and 100Hz. We’ll explain this more in the next section. But more than that, it means the unit first drops the level and then boosts it again by using a valve design which ultimately adds harmonic distortion that in most cases adds depth to the sound.
This means that the signal level remains the same regardless of whether EQ is switched in or out, which is very useful when comparing a flat signal to an equalized one. This is needed to restore the signal level that is reduced when an audio signal is fed into the unit, making the EQP-1A a no-loss passive equalizer.
#Pultec equalizer schematic full#
The Pultec EQP-1 is a full passive 3U all-valve equalizer and therefore needs an additional amplifier circuit. But what éxactly does this Pultec equalizer do that makes it so special, we can hear you asking.
#Pultec equalizer schematic manual#
They were in high demand by radio stations, where they were installed to “add that ‘final touch’ to the balance of good programme material and to greatly improve the quality of programme material previously recorded on equipment of inferior quality”, as the original manual boasted. In the meantime, the Pultec EQP-1A was very well received, probably due to the fact that it was the first passive program equalizer on the market. The build quality and design of all the Pultec products was unparalleled and each and every Pultec was handmade to order. Summerland and Shank hand-built the first units and through many iterations, the basic design remained through the late 70’s/early 80’s. You see, the first Pultec (EQP-1) was already introduced in 1951 by Pulse Techniques, a company formed by Ollie Summerland and Gene Shank in Teaneck, New Jersey, USA. So we felt it was time to demystify this unique device!īut first, let’s start with a bit of history And if you ask someone why only a few would have an answer to this question. It’s such an extraordinary piece of gear that people love putting it on their master bus, even without any EQ enabled. But there’s hardly any piece of gear that is more revered to about its magic, than the Pultec EQ. They all add character to your sound, something intangible, a little bit of mystery. We love classic analog gear! In previous blog articles, we already covered some of the finest like the Binson Echorec, SSL EQ’s, the Mini Moog, VOX AC30 and the NEVE 2254. By Robin Reumers (Edits: Milou Derksen, Dennis Beentjes)
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