Meet the Legend: Pultec EQP-1A

aka Tube Program Equalizer


If there is a holy grail of vintage tube equalizers, the Pultec EQP-1A is certainly it.


Pultec EQP-1A-Tube-Program-Equalizer-diy-by-analogvibes-history

Travel back in time...

…to learn about the founders of Pulse Techniques, what was  so  special about it and of how the EQP-1A was created back in the days… read more>>


Pultec EQP-1A-Tube-Opto-Compressor-diy-by-analogvibes-specs

what it actually is...

…that makes people think of the the EQP-1A as the holy grail of vintage tube equqalizers. Facts & figures behind the myth…  read more>>

how it works


What it does...

…and how it actually works. What is a passive equalizer after all. What makes the EQP-1A different from other passive EQs out there… read more>>



How 2 built 1...

…of these iconic pieces of gear yourself! I’ll show you the first and most important steps to build an authentic passive tube EQ from scratch…read more>>

tube program equalizer


early 1950s

Eugene Shenk, who had been working at RCA for 14 years and Ollie Summerland, who had been working at Capitol Records – both skilled electronic engineers established Pulse Techniques in Teaneck, New Jersey

early 1950s

PulTec (abbreviation of Pulse Techniques) initially designed power supplies for tube equipment and audio oscillators but as a former colleague of Summerland moved to MGM to build a mastering studio, Pultec was ordered to build a mastering equalizer.

1951 – 1952

For MGM Shenk designed a passive equalizer followed by a push-pull tube amp to make up for the loss in gain caused by the passive filter circuit.

The result was the EPQ-1 Program Equalizer.

1951 – 1952

The EQP-1 Program Equalizer was introduced to the wider studio industry and it was pretty much a game changer on how a signal could be altered during recording or in a mix.


Around the same time the Pultec EQP-1A was introduced. Other than the EQP-1 which had a fixed 10k attenuation control, the EQP-1A made the high frequency attenuation selectable between 5Khz, 10Khz and 20Khz. Furthermore the EQP-1A offered two more  high frequency boost options (4Khz + 16Khz).


The EQP-1A quickly found its way into many top recording studios – across the US and around the world. Tamla Motown owned several units and Motown engineers were among the first to utilize the “low-end trick” the EQP-1A is known for.

1953 – 1969

Several versions of the passive tube EQ design were developed by Pultec. Among the more known ones was the 2 rack units version of the EQP-1A – the EQP-1A3 and the midrange companion MEQ-5.  But also the less known EQH-2 equalizer is an amazing piece of gear (kind of a EQP-1 filter design with an MEQ-5 tube amp). 

1953 – 1969
1953 – late 1970s

During all that time the Pultec company only consisted of the two founders – Shenk & Summerland who meticulously built all units by hand. Maybe that’s why many Pultecs still do their magic in top studios around the globe to the present day.

1953 – late 1970s

Pultec introduced a solid state version of the EQP-1A3. In this version the push-pull tube amp was replaced by a single-ended type op-amp. Supposedly they are a little bit on the cleaner side but still wonderful EQs – praised by many top engineers – especially for bus applications.


After working with the original Pultec designer Eugene Shenk for more than 10 years, Steve Jackson finally brought Pulse Techniques and most of the original products back to life. The reissues are said to be built to original specs with no compromise.


Martin Zobel out of Germany builds a 100% authentic re-creation of the original EQP-1A from scratch and makes it available as a diy project through analogvibes.


analogvibes introduces the Tube Program Equalizer – a complete do-it-yourself kit including all components and chassis parts – true-to-the original design.




Bypass switch bypasses the filter section of the EQ, but the signal still passes the amp.

Low frequency boost & attenuate at the selected frequency.

Low frequency selection switch to choose the frequency for both, boost and attenuation at the same time. Sounds weird but that’s where that “Pultec trick” for kick or bass is coming from…

Boost at the selected frequency.

Bandwith controls the q-factor of the high frequency boost.

High frequency selection switch to choose the frequency for boost only!

Cut at the selected frequency.

High frequency selection switch to choose the frequency for cutting only!


High frequency filter unit. This box contains all filter caps and the inductor for high frequency boost and attenuation.

Peerless S-217D output transformer.

ECC-83 (12AX7) tube for the first gain stage of the tube amp.

6×4 rectifying tube of the power supply.

Low frequency filter unit. This box contains all capacitors for low frequency boost or attenuation. In the vintage units caps and inductor in both boxes were potted in bees wax.

Triad HS-29 interstage transformer.

Audio input & output connections screw terminal – no XLRs on vintage units!

ECC-82 (12AU7) tube drives the output transformer.

Triad HS56 (or HS56V) input transformer.

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how it works...

Part I - Overview Pultec EQP-1a

This is a first introduction and overview of the iconic tube program equalizer explaining the controls as well as the major components on the back.

Featured: The Pultec EQP-1A in action.

In this great video Doctor Mix shows the EQP-1A in action. In case you never used a real Pultec EQP-1A before, this will give you good first impression.

more videos are coming soon...

Have a look at the LA2a-project page to get a feeling what’s coming.


Everything was better before - well, NOT!

The "Build Your Legend Series" including several epapers on how it works, a modern wiring layout and the ultimate analogvibes step-by-step guide is coming very soon.

Have a look at the LA2a-project page to get a feeling what’s coming.

For now, we already provide a complete BOM and a wiring layout. Not perfect yet, but a good start.

One more thing...

The Ultimate Complete Tube Program Equalizer Kit is available now. Update: Pre-order are closed.

Got a question? You can ask us everything you want...

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There are a lot of very nice and extremely qualified fellows (way more then Martin ;-), who would gladly help you out.