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$299.00 $259.00 ex. VAT

Fully Assembled and Tested!

  • Mix and Match HRK 500 Products!
  • Buy VAT FREE with EU VAT Number
  • NO VAT for Orders from Outside EU
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Product Description

EQ550P | Passive Valve Two Bands Equalizer

  • 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.

Basic Demo Video

Track from the Basic Demo Video:


Kick Drum Demo Video

Track from the Kick Drum Demo Video:


Stereo Demo Video – HD Audio

Track from the Stereo Demo Video:



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

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.


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

We offer Fast & Free Worldwide UPS shipping with tracking.

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

Total cart value / Delivery cost:

up to 99USD / Delivery Cost – 19.99USD

99 – 148USD / Delivery Cost – 14.99USD

149 – 248USD / Delivery Cost – 9.99USD

over 249USD – FREE Delivery

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

Total cart value / Delivery cost:

up to 148USD / Delivery Cost – 19.99USD

149 – 298USD / Delivery Cost – 14.99USD

over 299USD – FREE Delivery

Please check the shipping cost during the checkout.

Delivery to other WorldWide destinations – 24.99USD

VAT and Customs Fees

For non-business orders from the EU, the VAT will be added at the checkout.

VAT is removed automatically for orders from outside the EU.

No Custom Fees for EU Customers.

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

EU Business Customers

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.

The VAT number is automatically checked in the VIES database.

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!

Return Policy

Our return policy is a part of the general Terms & Condition which you have to acknowledge at the checkout.

We stand for fair rules and a win-win approach. We understand that our customers may wish to return the product and we do provide such option. However, because we are a small company we can’t afford to run a grade B outlet shop like big distributors and provide the 30 days return period.

We can’t also scrap every returned unit. We could charge our customers more to offset the cost of the returns, this is what major distributors do. Or we can keep our prices low and hope that our customers will appreciate our policy.

This is why we provide the 7 days test period after receiving the package with the ordered items and if you wish to return the item we will accept the return request, providing that the item is not damaged and we can resell the product with the minimal loss for the company.

If the item is damaged during the transport we will do our best to help you and provide the replacement product.


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