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


The DIYRE EQP5 and the HRK EQ550P are the passive Pultec inspired equalizers. This page compares the main features and highlights the difference between both units. This page should be treated as the guide for the website visitors and the FAQ section.

The main features of the DIYRE EQP5 and the HRK EQ550P colour mic preamps are presented and compared in the table below.




Number of Bands 2 2
Frequencies HF Band 10kHz / 16kHz (20kHz) 6kHz / 10kHz / 16kHz
Frequencies LF Band 60Hz / 30Hz 50Hz / 80Hz / 160Hz
EQ Filters Type Capacitors + 1 Inductor Capacitors Only
Adjustable Q YES (PCB Trimmer) NO
Gain Stage Type Integrated Circuit (IC) Opamp OR Discrete Opamp Discrete Class A Circuitry with ECC83 Vacuum Tube
Output Stage Electronic Balanced (IC) OR Transformer Class A Discrete Driver + Transformer
Input Stage Electronic Balanced Electronic Balanced


The DIYRE EQP5 and the HRK EQ550P share the same topology of the equalizer section. Each Band consist the independent Boost and Cut knob for HF and LF section, which makes four knobs in total. The frequencies for each band can be selected individually for Cut or Boost knobs. This creates a lot of options for creating custom EQ curves. The DIYRE EQP5 has two frequencies which can be selected for each Boost or Cut knob, while the HRK EQ550P has three frequencies to choose from for each Boost or Cut knob.

The Filter Type.

Although both units are inspired by the famous Pultec EQ, there are some differences between the EQ filter design. It seems that the DIYRE EQP5 follows more accurately the original design and provides the adjustable Q option with PCB trimmer. Furthermore, the filter section consists the single inductor which suggests that the HF response might be limited above 20kHz depending on Q setting. This assumption was made after analyzing original Pultec EQ schematic.

The HRK EQ550P is a pure shelf EQ and it has no provision for Q factor adjustment and no inductors. No limitation in HF band is added and the HF response continues up to 120kHz where it starts to slope down naturally. Such design of the circuit is optimised for Air frequencies and harmonics which are produced by the ECC83 valve and the output transformer.

The Gain Stage and the Output Stage.

The passive EQ filter section needs the gain stage to work properly. The EQP5 offers two options. First is the stock IC based gain stage OR the premium Discrete Opamp gain stage + the Transformer output stage. The user has to make the selection with the PCB jumper.

The EQ550P has only one option available. The ECC83 Valve / Discrete Class A gain stage and the Transformer output stage with the separate no-feedback, Discrete Class A driver.

The Price.

The DIYRE EQP5 is available as a DIY KIT starting from 200USD for the basic option – no Discrete Opamd and no output Transformer and the 269USD for the premium option with Discrete Opamp and the Output Transformer. The assembled version costs 300USD for basic option. There is no price available for the assembled premium option with the Discrete Opamp and the Output Transformer.

The HRK EQ550P is available only as an assembled and tested unit with the ECC83 valve stage and the output Transformer in standard option for less than 250USD.

Back to EQ550P product page ->