$599.00 $499.00 ex. VAT

  • Mix and Match HRK 500 Products!
Promo Qty Discount
500 Mix & Match 2 - 3 10%
500 Mix & Match 4 - 5 15%
500 Mix & Match 6 + 20%


EQ550P | Passive Valve Two Bands Equalizer – MATCHED PAIR

  • Inspired by Famous Valve Passive EQ
  • Hybrid Tube Class A Gain Stage
  • Two Bands Shelf EQ Operation
  • 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 Discrete Output Transformer Driver
  • JJ Electronics ECC83 Dual Triode Tube
  • On-Board Voltage 500 Rack PSU Filters
  • Direct Sale – Save on Distributors Fee!

This is the EQ550P matched pair offer – two units with EQ curves.

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 reaches tone while maintaining the noise on the extremely low level.

Create 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.

Standard Cut and Boost Curves

Like any other equalizer, the EQ550P can be used to cut or boost the shelf frequencies.

The plots below show the maximum cut and boost for each band and frequencies settings.

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 modules, 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.

Discrete Transistor Class A Output Transformer Driver

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

Acoustic Guitar Demo Video

Acoustic Guitar Demo Track

CP523V set to moderate compression settings. Slow Attack, Medium Recovery, HPF- IN

      Acoustic Guitar - Dry
      Acoustic Guitar - CP523V

Female Vocal Demo Video

Female Vocal Demo Track

CP523V set to moderate compression settings. Slow Attack, Medium recovery, HPF- IN

      Female Vocal - Dry
      Female Vocal - CP523V

Drums Demo Video

CP523V set to moderate compression settings. Slow Attack, Fast Recovery, HPF- IN

      Drums - Dry
      Drums - CP523V


DIYRE EQP5 Passive Equalizer vs EQ550P Valve Passive Equalizer – Comparison Page ->

Item Condition

Brand New, Assembled and Tested.

Every single HRK product is carefully tested with Audio Precision test equipment before the shipping to ensure hassle-free operation.

Payment & Shipping


All Items are dispatched from the European Union within 1-3 working days.

We offer fast worldwide UPS shipping with tracking.

FREE delivery is available for orders over the 249USD to EU, USA and Canada.

FREE delivery is available for orders over the 299USD to Australia, New Zeland, Japan and other destinations.

Please check the shipping cost during the checkout.

Delivery to other WorldWide destinations – 24.99USD

EU Business Customers

All prices exclude the VAT Tax.

If you have the EU VAT number you can purchase the products available in the Bart HRK Shop with no VAT Tax.

Please enter your EU VAT Number at the checkout and the VAT will be deducted from the Total Payment.

Non-EU Customers

Customers from outside the EU can purchase the items with no VAT.

Please select the destination country and the VAT will be removed automatically.

If the VAT is not removed, please email customer service via the contact form and custom invoice will be issued.

Orders from the USA below 800USD are customs tax-free.

Payment Options:

You can pay for your order with any Credit Card



Input impedance: 10kOhm

Output impedance: 100R

Phase inverse: none

Gain: 0dB

All HRK Colour Modules are fully compatible with DIYRE Colour Format

All HRK Colour Processor and Preamps fully compatible with DIYRE Colour Format

All HRK 500 products are fully compatible with API 500 Format

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