WHAT IS THE EQP?
Let's look at the real thing and see what AudioScape has cloned. The original Pultec EQP-1, developed by Pulse Techniques (Pultec), is a legendary audio equalizer introduced in 1956, widely revered for its musical sound and versatility in professional recording studios. It was designed by engineers Eugene Shenk and Ollie Summerlin to meet the needs of recording studios, offering a significant improvement over the noisy, lossy equalizers used in the film industry at the time. The EQP-1 and its variants, particularly the EQP-1A, became studio standards.
EQP HISTORY
- 1956: The EQP-1 was released as Pultec’s first program equalizer, housed in a 3U rack mount chassis. It featured a passive equalizer design with a tube amplifier stage to compensate for signal loss, making it practical for broadcast and recording applications.
- 1961: The EQP-1A replaced the EQP-1, adding frequency selections (20 Hz boost/attenuation, 16 kHz boost, and 5/10/20 kHz attenuation) for greater flexibility.
- 1971: The EQP-1A3, a 2U version of the EQP-1A, was introduced with identical circuitry. A solid-state version, the EQP-1A3SS, later replaced tubes with transistors.
- 1981: Production ceased as Shenk retired, but a final run of EQP-1A3 units was made for Power Station studios.
- 2000: Pultec resumed production, with Steve Jackson leading efforts to recreate the original EQP-1 and EQP-1A designs faithfully.
- Post-1980s: The EQP-1’s popularity led to recreations by manufacturers like Tube-Tech (PE 1A, 1985), Manley Laboratories (Enhanced Pultec, 1990), Cartec (EQP1A, 2010), Warm Audio, Klark Teknik, and others.
Circuit Design: Passive EQ with a tube amplifier stage (12AX7/ECC83 for input, 12AU7/ECC82 for output) in a push-pull configuration, using transformers for balanced I/O and negative feedback to minimize distortion.
Low-Frequency Section: Shelving EQ with boost/cut at 30, 60, 100 Hz (EQP-1); added 20 Hz in EQP-1A. Boost up to 12 dB, cut up to 24 dB.
High-Frequency Section: Boost at 3, 5, 8, 10, 12 kHz (EQP-1); added 4 and 16 kHz in EQP-1A. Cut at 10 kHz (EQP-1); added 5, 10, 20 kHz in EQP-1A. Bandwidth control adjusts Q from sharp to broad.
Tubes: 12AX7 (input) and 12AU7 (output), contributing to the characteristic warmth.
Transformers: Input and output transformers add subtle harmonic distortion, enhancing the “musical” quality.
The EQP-1’s design allowed simultaneous boost and cut at low frequencies, creating unique phase effects that became a signature technique (e.g., boosting bass while cutting midrange for clarity). Its tube-based Class-A circuitry and transformers contribute to its revered “warm” and “musical” sound, making it a favorite for vocals, drums, and mastering.
AUDIOSCAPE EQP-A
AudioScape’s EQP-A is designed as a faithful recreation of the original Pultec EQP-1A, with meticulous attention to replicating its sonic character and technical specifications. The AudioScape EQP is built in their 3RU, rack mountable, steel chassis, this is very similar to the chassis used on their V-comp and Opto models.
Build Quality:
Handcrafted in the USA, the EQP-A uses NOS components (e.g., carbon comp resistors) and point-to-point wiring connecting with modern circuit board construction. Unlike the original’s fixed power cable and terminal strip I/O, the AudioScape EQP uses modern IEC connectors and XLR I/O for practicality, a minor deviation that doesn’t affect sound quality.
Circuit Design and Components: AudioScape claims to have spent over a year on R&D, uncovering and correcting errors in the original schematics that affected high-end response, ensuring their EQP-A behaves like vintage units. They emphasize “no component compromises” and “Sonic Truth,” aiming to replicate the original’s passive EQ circuit and tube amplifier stages.
Tubes: The EQP-A uses NOS (New Old Stock) tubes, including the 12AX7/ECC83 (input), 12AU7/ECC82 (output), and the often-omitted 6X4 rectifier tube, matching the original’s tube complement for authentic sound. Chris (one of the AudioScape owners) has told me (more than once) that he believes the rectifier tube in vintage circuits adds to the sonics and audio reproduction of processors like the EQP-A and the V-Comp. My vintage Mesa Dual Rectifier amps live in the Tube Rectifier mode, I've listened to the Silicon mode and I like the Tube mode better, so Chris is right about rectifiers playing a role in the sound, in a positive way!
Transformers and Inductors: The EQP-A features a custom-wound input transformer, custom made inductor and custom output transformer (recreating the rare Peerless S-217D), all critical for the Pultec’s characteristic “box tone” and harmonic richness.
Interstage Transformer: Unlike many clones that omit it, AudioScape includes the interstage coupling transformer, which they claim contributes significantly to the original’s sound.
EQ Curves and Functionality:
The EQP-A replicates the EQP-1A’s two-band passive design, with low-frequency shelving (20, 30, 60, 100 Hz) and high-frequency shelving boost (3, 4, 5, 8, 10, 12, 16 kHz) and cut (5, 10, 20 kHz), including the bandwidth control for variable Q.
AudioScape’s EQ curves are said to be “accurate to vintage specs,” ensuring the broad, musical boosts and cuts that define the Pultec sound. To my ears these pieces sound very musical and dare I say, "High Fidelity".
Technical Specifications Comparison
While exact specs for the original EQP-1A vary slightly due to its age and lack of standardized documentation back then, AudioScape’s EQP-A aligns closely:
- Frequency Response: 20 Hz to 20 kHz, ±1 dB, matching the original’s wide bandwidth.
- Distortion (THD+N): < 0.1% at 1 kHz, +4 dBu, reflecting the original’s low-distortion Class-A push-pull design.
- EQ Functionality: Identical frequency points, boost/cut ranges, and bandwidth control as the EQP-1A, with no added frequencies or features that deviate from the original.
AudioScape’s EQP-A adheres very closely to the original Pultec EQP-1A, replicating its circuit design, tube complement, transformers, and EQ curves with obsessive attention to detail. By using NOS components, it may even outperform some vintage units in consistency while retaining the iconic “Pultec sound.”
Advanced Testing and Mixing
Most of the time, I’ve been using the EQP-A connected to my Coleman Audio Transfer Console (< full review on H.o.T.) which allows four separate mastering processors to be individually switched completely in or out of the signal path for accurate A-B comparisons while mixing, (something you can’t do with the bypass switch on the EQP-A). I’m using a pair of EQP-A in insert #One of the Coleman and this pair of AudioScape V-Comps (< full review on H.o.T.) for buss compression in insert #Two. I love being able to switch the processors completely in or out of a mix for fine tuning settings, this really helps you hear the nuances each processor is contributing.
The Coleman console also allows the integrity of a processor's sound to be examined closely and hear whether it is affecting the sound negatively; I never heard the slightest hint of badness from the EQP-A.
EQP-A Specifications
- Circuit Design: Class-A, push-pull tube amplfier
- Input and Output: Transformer balanced
- Tubes: 12AX7/ECC83 (input), 12AU7/ECC82 (output)
LIKES
- Great sounding and useful equalizer
- Handmade in small batches
- Doesn’t degrade your mix
- Authentic and accurate “Sonic Truth” for comparatively low price
- Tubes are not sticking out the back
DISLIKES
- Large chassis size (like the original, takes up a lot of rack space)
- No TRS inputs and outputs
- No full bypass - "bypass" still feeds through transformers and tubes
- Not enough venting on the chassis, needs rear vents for additional air flow
EPILOGUE
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| Pair of EQP-A in the High on Technology Studio, click to enlarge |
I appreciate that AudioScape has brought these exotic, vintage style, tone processors, down to Earth with authentic reproduction and handmade, factory-direct, affordable pricing. I’m continuously comparing gadgets and so far, the AudioScape can't be beat - their smooth, low-noise performance and excellent sonics make them a solid, repeatable, Go-To for me. Apparently other folks also think these are cool because the current wait time to get an EQP-A is 5-7 weeks.
AudioScape products have a two year warranty and are sold direct to end users from their web site. So far I’ve added six pieces of AudioScape gear to the High on Technology studio and these are all used regularly, so it is safe to say I like them a lot and yes, they are good!
With the exception of one N.O.S. tube going bad in one of my V-Comps I’ve never had the slightest bit of trouble from any of my AudioScape pieces (their service department got me replacement tubes for the V-Comp in four days, they even answered my service inquiry on SUNDAY, try that with one of the big brands :-)
You can do different but you can’t do better than AudioScape without dropping monumental amounts on vintage originals (which might be plagued with problems - bad switches, failing caps - due to age) or some other clone with unknown credentials (other than a high price). I’m a big fan of AudioScape studio gear - it's reliable, sounds great and is priced right.
Hand built by humans, in small batches, is alive and well at AudioScape in Daytona, Florida.
Thanks for reading High on Technology, Good Music To You!
©May 2025 by Mark King, it’s not ok to copy or quote without written permission from the author.
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| Note the air gaps between the units to allow for more cooling, tubes gotta breathe |
Go forth and create something beautiful……………
