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EQ550P | Passive Valve Two Bands Pultec Style EQ
Old 19th January 2019
  #1
Here for the gear
 
Bart_UK's Avatar
 

EQ550P | Passive Valve Two Bands Pultec Style EQ

EQ550P | Passive Valve Two Bands Pultec Style EQ
  • Inspired by Famous Valve Passive EQ
  • Hybrid Valve Class A Gain Stage
  • Two Band Shelf EQ Design
  • Separate Control for Boost and Cut
  • 3 Frequency Settings for HF Band
  • 3 Frequency Settings for LF Band
  • Vintage NOS Discrete Components
  • Output Coupled with Custom HRK Transformer
  • Class A Output Transformer Driver
  • JJ Electronics ECC83 Dual Triode Tube
  • On-Board Voltage 500 Rack PSU Filters
  • Direct Sale – Save on Distributors Fee!

The EQ550P is a Passive Tube based 2 Band Shelf Equaliser inspired by the famous Pultec design.

Each Band has a separate Boost and Cut Control which allows creating the sophisticated EQ curves.

Each Boost or Cut control has three different and independent frequency settings which give a total of 9 setting combinations per Band.

The Passive filter section changes the EQ curve by attenuating the signal. The ECC83 gain stage restores the signal to the nominal level adding the combination of harmonics and transients.

The EQ550P is very musical and easy to use. It can process any music material, instruments, vocal or recordings, producing amazing results.

The Valve – Discrete Transistors Hybrid circuit is the result of a long development process. It produces real Tube harmonics and reach tone while maintaining the noise on the extremely low level.

Create the Sophisticated EQ Curves!

The unique feature of Passive Equalizer is the ability to Cut and Boost at the same time.

The EQ550P can create the sophisticated EQ curves which cannot be achieved by the active shelf equalizers.

Ability to select three different frequencies independently for Cut and Boost provides countless possibilities in creating custom EQ curves.

Pictures below show a few examples of such EQ curves.


Hybrid Valve Gain Stage

“Valves can work only with high voltage” – this is the common myth repeated across the internet by self-acclaimed “experts” which have no experience in electronics.

The truth is that most of the popular valves can work with lower voltages without the problems. The key to the success is the clever solution for biasing the valve.

Specially designed discrete transistor circuit controls the biasing and forces the tube to operate as intended at the harmless anode voltage.

The result is a perfectly stable valve gain stage with standard ECC83 dual triode, which delivers 26dB of noiseless gain.


Coupled with Custom HRK Transformers

The Output of the EQ550P is coupled with specially designed custom HRK Transformers. Because of limited space in the 500 module, HRK Custom Transformers became smaller, maintaining no-compromise performance.

All HRK transformers provide the sweet-spot sonic characteristic with pristine detail reproduction. The goal of the design process was to create the transformer which will deliver a balance between the transparency and colouration typical for transformer stages.

Dicrete Transitor Class A Output Transformer Driver

The output transformer is powered by Class A, No-Feedback, DC-Coupled Discrete Driver built with NOS Transistors from ’70s.

More Info, Demo Video and Sound Samples available at:
EQ550P | PASSIVE VALVE 2 BANDS PULTEC STYLE EQ
Attached Thumbnails
EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-valve-pultec-eq.jpg   EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-fp.jpg   EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-valve-pultec-eq-2.jpg   EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-tube-pultec-eq-hf-curves.jpg   EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-tube-pultec-eq-hfmm-curves.jpg  

EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-tube-pultec-eq-lf-curves.jpg   EQ550P | Passive Valve Two Bands Pultec Style EQ-eq550p-passive-tube-pultec-eq-lfmm-curves.jpg  

Last edited by Bart_UK; 19th January 2019 at 07:48 PM..
Old 21st January 2019
  #2
Lives for gear
 
retractablezing's Avatar
 

Hey Bart, this looks neat. I've got a question, though: the only iron i see looks like an inductor, but that would be the output transformer, correct? So no inductors in the circuit?
Old 22nd January 2019
  #3
Gear Nut
 
Jeb A's Avatar
 

Intriguing
Old 27th February 2019
  #4
Gear Maniac
 
stylesforfree's Avatar
 

Did anyone pick one of these up? Im thinking about selling my 2 Lindell PEX-500 and replacing them with these.
Old 7th March 2019
  #5
Here for the gear
 
Bart_UK's Avatar
 

Quote:
Originally Posted by retractablezing View Post
Hey Bart, this looks neat. I've got a question, though: the only iron i see looks like an inductor, but that would be the output transformer, correct? So no inductors in the circuit?
No inductors, the output is coupled with the custom made HRK transformer and the no-feedback discrete driver.
Old 8th March 2019
  #6
Lives for gear
 
jitterybit's Avatar
Quote:
Originally Posted by Bart_UK View Post
No inductors, the output is coupled with the custom made HRK transformer and the no-feedback discrete driver.
So, no indictors and the make-up gain stage is transistor based.
How is this "pultec style"?
No doubt that it could sound great, but the only thing I see similar to a Pultec is the toob(and maybe the equipment curves).
Not trying to dog on you here, but the electrical engineer and the audio engineer that live in my mind can't agree.
Old 8th March 2019
  #7
Lives for gear
 
retractablezing's Avatar
 

Quote:
Originally Posted by jitterybit View Post
How is this "pultec style"?
You know, the way I see it, that can be said of most of the "clones" out there, some more than others, obviously. Most lack the interstage iron, etc. So, in fairness, as long as the curves are close and one can boost/cut simultaneously, I'd say "Pultec Style" is fair game. It certainly looks inspired by it. Again, just my opinion.

Last edited by retractablezing; 8th March 2019 at 12:18 PM..
Old 8th March 2019
  #8
Here for the gear
 
Bart_UK's Avatar
 

Quote:
Originally Posted by jitterybit View Post
So, no indictors and the make-up gain stage is transistor based.
How is this "pultec style"?
No doubt that it could sound great, but the only thing I see similar to a Pultec is the toob(and maybe the equipment curves).
Not trying to dog on you here, but the electrical engineer and the audio engineer that live in my mind can't agree.
Pultec EQ's are a group of many different types of passive equalizers. The common between all models is the passive attenuating filter section with specific capabilities and curves and gain make-up circuit.
Some versions or variations of the Pultec design consists pure valve circuit, some transistors or even opamps...

I have explained why I have decided to use the hybrid valve circuit on my page. I have a lot of experience in designing such circuits. They perform as good as many valve only circuits, providing better noise performance and fewer problems with HT supply. They are SAFE, which is a serious issue when it comes to 500 units...

As you are probably aware, the inductors are not the necessary component to create the shelf LF/HF EQ. The inductor which is in the HF section of the Pultec filter circuit will in fact cut off the high-frequency response, creating more bell type response, instead of pure shelf response. Hence the Q potentiometer. I decided to remove the inductor to leave the pure shelf response, not limiting the response in the 20kHz+ region, so the EQ will have HF "air".

Inductors have wider tolerance and can pick-up interferences from the PSU.
The sound won't get better only because the inductor is used in the circuit. The use of the inductors in vintage equipment was the result of a specific design decisions made by designers of the era. Usually, because there was nothing better available at the time. Same goes for valves...

I'm not claiming that the EQ550P is a 1:1 Pultec clone... It is "Pultec type" or "inspired by". It has the most important features of the Pultec type EQ, including curves. It is also affordable, which was the goal.

The original Pultec EQP-1A costs 4K and quite often is beyond the reach of many music enthusiasts... and if somebody has the money to spend on the original Pultec unit, then it won't be interested in clones anyway...
Old 4 weeks ago
  #9
Here for the gear
 

Would love to hear from anyone who owns or has used one of these
Old 4 weeks ago
  #10
Couldn't resist the very low price and the demos where to good to ignore... just bought a pair! And several pairs color modules, US Pentode and EZ Ge Eq and Ge Console!
Can't wait to get them all in my Rack 500!
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