Travel back in time...
what it actually is...
how it works
What it does...
tube program equalizer
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
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.
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.
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.
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).
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.
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
Featured: The Pultec EQP-1A in action.
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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.
For now, we already provide a complete BOM and a wiring layout. Not perfect yet, but a good start.