Pultec Equalizer Schematic: The History and Evolution of the Iconic EQ

Anyone who has every played a traditional electric guitar or Bass guitar has adjusted a passive equalizer. The tone controls of these instruments are a great example of a passive High frequency control. In fact the Pultec High Frequency " Atten" control works very much like this.

Notice how the signal travels into a Passive equalizer circuit first. It is important to understand that when all the controls of the Pultec are set to '0' the EQ circuit has "gain" of -15 dB. That's right, the signal has to be reduced by default if we want to make a boost circuit because a Passive EQ cannot amplifiy a signal!

Pultec Equalizer Schematic

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Simply, the key to the tone of these two circuits are its amplifiers, and Mercury EQ-P2 and EQ-H2 have different amplifiers to make up the gain lost by the passive equalizer circuit, thus they have different tones. The EQ-P2 and EQ-H2 sound different on the same application, and have a different reaction to the same instrumentation or voice.

The EQ-P2 is more open and silky, and equally adds warmth to highs, mids and lows of your source. The EQ-H2 is more punchy and robust and has a slight push in the low end and lower midrange. Although both sound amazing on any application and are both multi-purpose tools (equalizers) in the studio, if you had both you could then choose between applications.

The Mercury EQ-H1, EQ-P1, EQ-H2 and EQ-P2 are all based on the original Pultec equalizers which were tools developed to deal with the limitations of recorded music. Limitations that most often manifest themselves in the highest and lowest frequencies of the program material. The Mercury Studio Program Equalizers, like the family of original Pultec EQs, were originally designed to bring back the life and musicality lost in a recording. Whether by accident or genius, nothing has been able to do this better in music production than a passive equalizer with tube gain make up amplifier ('Pultec style') equalizer. The interaction of the passive boosting and attenuating shelving EQs (not relying on negative feedback), as well as the transformers, tubes and other amplification circuitry all add to the incredibly musical character of the product. Working engineers try other types of equalizers, but always end up coming back to the Pultec style as the equalizer of choice for those final touches while tracking, mixing and mastering.

As I was interested even more in the later model, I studied the 1968 schematic mainly because nicely as several, many photos of these products, and developed the extremely popular 1968 Are generally2a wiring layout.

The Mercury EQ-H1, EQ-P1, EQ-H2 and EQ-P2 are all based on the original Pultec equalizers which were tools developed to deal with the limitations of recorded music. Limitations that most often manifest themselves in the highest and lowest frequencies of the program material. The Mercury Studio Program Equalizers, like the family of original Pultec EQs, are originally designed to bring back the life and musicality lost in a recording. Whether by accident or genius, nothing has been able to do this better in music production than a passive equalizer with tube gain make up amplifier ('Pultec style') equalizer. The interaction of the passive boosting and attenuating shelving EQs (not relying on negative feedback), as well as the transformers, tubes and other amplification circuitry all add to the incredibly musical character of the product. Working engineers try other types of equalizers, but always end up coming back to the Pultec style as the equalizer of choice for those final touches while tracking or mixing and even mastering at times.

Simply, the key to the tone of these two circuits is its amplifier, and Mercury EQ-H1 and EQ-P1 have different amplifiers to make up the gain lost by the passive equalizer circuit, thus it has a different tone. Meaning the EQ-H1 and EQ-P1 sound different on the same application, and have a different reaction to the same instrumentation or voice.

The EQ-H1 is more punchy and robust and has a slight push in the low end and lower midrange. The EQ-P1 is more open and silky, and equally adds warm to highs, mids and lows of your source. Although both sound amazing on any application and are both multi-purpose tools (equalizers) in the studio, if you had both you could then choose between applications.

The TUBE-TECH PE1C is a passive tube based program equalizer based on the design of the old PULTEC EQP1A, featuring an all passive eq section and a high quality op amp. All components used are of the highest standard.

The PEQ Filter PCB is a high quality Filter PCB to build a passive equalizer project. The filter circuit is based on the vintage EQP-1A with a great range of additional frequencies. Optimized grounding, audiophile designed signal pathes and a nice selection of the best parts for each frequency-band make this PEQ sounding outstanding. Classi PEQ is compatible with the sweet sounding EF inductors that come close to the original Pultec Inductors, RM-Inductor or there is an additional pin-bank to wire up any vintage Inductor with similar specifications, Sifam, Cinemag or the original Pultec Inductor. Classi PEQ is compatible to tube SRPP stages and can be used for example with the GPultec SSRP stage or the OPA stage as well. The Full Filter Kit includes pre-confectioned wires that allow wiring pots and switches fast and easily. With this filter board you can reproduce any kind of the modern or vintage passive equalizer frequency pattern - just wire up the required frequencies you wish to controll on your front-panel.PEQ Frontpanels

RB500ME is a stereo passive equalizer packed into a double 500-series module. This beast is equipped with transformer balanced inputs and outputs (IGS Custom) as well as a class-A driver circuit.Of course, the entire filtering section is passive and it mirrors analog equalizers from the 60s. There is a separate frequency selector for low cut and boost sections.Top quality potentiometers and ELMA switches were used to achieve outstanding performance. 2ff7e9595c