EQ573-II - EQ 500 series, Neve style - DIY Analog Pro Audio
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  • EQ573-II - EQ 500 series, Neve style - DIY Analog Pro Audio
  • EQ573-II - EQ 500 series, Neve style - DIY Analog Pro Audio

EQ573-II Equaliser for the series 500

$459.00
$459.00 VAT incl.
$459.00 VAT excl.

The EQ573-II is an parametric equalizer based on the design that was originally used in the Neve 1073 and 1084 modules, that has been adapted to the '500' format of API*.

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EQ573-II

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The EQ573-II is an parametric equalizer based on the design that was originally used in the Neve 1073 and 1084 modules, that has been adapted to the '500' format of API*.

The EQ573-II can be used as a standalone unit but also as an insert, between the input and output stages of the MP573 mic pre, recreating the full architecture of the 1073.

the EQ573-II is the successor to the EQ573. The improvement mainly concerns the ease of assembly and the reliability of the final product. The audio behavior is the same, the only differences being the lack of attenuation when inserting into an MP573 and the removal of intermediate Q in the mid band.

Just install it in your API* compatible LunchboxTM rack and start recording.


Highlights

    • Three bands equalizer and high pass filter
    • High shelf EQ: +/-16dB @ 10kHz, 12kHz, 18kHz, 20kHz, 25kHz
    • Mid EQ: +/-18dB @ 0.27kHz, 0.36kHz, 0.5kHz, 0.7kHz, 1.1kHz, 1.6kHz, 2.3kHz, 3.2kHz, 4.8kHz, 7.2kHz, 10kHz
    • Low shelf EQ: +/-16dB @ 20Hz, 35Hz, 60Hz, 110Hz, 220Hz
    • High pass filter: -18dB/octave @ 25Hz, 45Hz, 70Hz, 160Hz, 360Hz
    • Additional frequencies in all bands
    • 2 Q values for the mid EQ (1073 and 1084-Hi)
    • Pre/Bypass/XLR switch on the front panel allows both MP573 insert or standalone mode
    • Single ended, class A circuit
    • Carnhill inductors
    • Available assembled or as a full kit (everything included)

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Controls

1 High shelf corner frequency: From 10kHz to 25kHz (OFF=disabled).

2 High shelf level: Sets the high frequency attenuation or boost from -16dB to +16dB.

3 High Q Gain switch: Modify the Q of the mid frequency band.

4 Mid band center frequency: From 270Hz to 10kHz (OFF=disabled).

5 Mid band level: Sets the mid frequency attenuation or boost from -18dB to +18dB.

6 Low shelf corner frequency: From 20Hz to 220Hz (OFF=disabled).

7 Low shelf level: Sets the low frequency attenuation or boost from -16dB to +16dB.

8 Source Selects the source of the EQ between XLR and a linked MP573 preamp (OFF=bypass).

9 High pass filter: From 25Hz to 360Hz (OFF=disabled).


What's in the kit?

Absolutely everything!

  • Passive components (resistors, capacitors),
  • 2 Carnhill inductors
  • Active components (diodes, transistors, LED, ...),
  • Front panel elements (switches, potentiometers, knobs),
  • Connectors, relay,
  • PCB's,
  • Front panel and side panel,
  • All hardware

You bring the solder (use good quality solder, 1mm diameter max) and the Lunchbox.


Difficulty level

The EQ573 kit is a rather complex build because of the high components density.

PK008

Specific References


Technical specifications

Measure Conditions Value
Iddle supply current No input signal I = +/- 40mA
Input impedance f=1kHz on XLR 20kΩ
Maximum input level on input XLR +25dBu
Maximum output level before clip on output XLR +26dBu
High Freq maximum boost/cut   +/-16dB
Mid Freq maximum boost/cut   +/-18dB
Low Freq maximum boost/cut   +/-16dB
High pass filter attenuation   -18dB/octave

The Sound Skulptor EQ573-II (Revision 2.2) is a professional-grade, inductor-based equalizer designed for the 500-series format. It is a hybrid architecture combining high-performance operational amplifiers, discrete transistor gain stages, and passive LC (inductor-capacitor) filter networks.


1. Input Stage and Buffering

The signal enters the unit through the balanced IN+ (B10) and IN- (B8) pins. An OPA2134 operational amplifier (U1.1) serves as the initial input buffer. Relays (RLY1.1, RLY1.2) manage the bypass and routing, including an external Send/Return insert point at J2 which is used to insert directly in the MP573 preamp.


2. First Discrete Stage: Low and High Band Equalization

Following the input buffer, the signal enters the first of two discrete Class-A amplification stages.
  • Discrete Amplifier A: This stage is built using a trio of BC550transistors (Q1, Q2, Q3).
  • Feedback-Loop Filtering: Frequency shaping for the low and high bands is achieved by placing the filter networks within the feedback loop of this amplifier in a Baxandal style.
  • Low Frequency (LF) Band: Managed by the 47kA potentiometer (P2) and a bank of capacitors (C35 to C44) . Frequency selection is controlled by SW4.
  • High Frequency (HF) Band: Controlled by the 10kA potentiometer (P1) and capacitor bank C25 to C34. Frequency selection is handled by SW3.

3. Second Discrete Stage: Mid Frequency (MF) Equalization

The signal proceeds to a second dedicated Class-A gain stage for mid-range processing.

  • Discrete Amplifier B: Utilizes another set of BC550C transistors (Q4, Q5, Q6).
  • MF Band Filter: This stage features a passive LC filter in the amplifier's feedback loop (INb to OUTb).
  • MF Controls: Shaping is performed by the multi-tap L2 inductor and a series of capacitors (C48 through C59) selected by SW6 . Gain is adjusted via the 10kA potentiometer (P3).

4. High Pass Filter (HPF) and Output

Once the signal has passed through the three equalization bands, it reaches the High Pass Filter and output driver.

  • High Pass Filter: The output of the discrete stages (Node B) feeds the HPF section. This filter uses the L1 inductor in an LC configuration. The cutoff frequency is determined by SW1, which switches between capacitors C13 to C22 .
  • Output Driver: The filtered signal is buffered by the second half of the OPA2134 (U1.2) and then balanced for the final output by the THAT1646 line driver (U2). The balanced signal exits via OUT+ (B2) and OUT- (B4).

5. Power Supply and Voltage Rails

The unit utilizes the standard 500-series +/-16V power supply.
Protection: IN4004 diodes (D3, D4) provide polarity protection.
Discrete Audio Rails: Stable local voltage rails (V+a and Va-) for the discrete transistor stages are created using an RC filtering network with C83 (330uF) and C84 (1000uF) capacitors.


Build and review of the EQ573

Reviews

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Quality

Reinhard M
 04/02/2026

Great EQ - love it

After the LA502, the EQ573-II was the second module I built. The EQ is significantly more complex than the compressor. The most important thing — and here I agree with the previous speakers — is to take your time. You have to work very carefully, especially when mounting the many capacitors. If you work neatly, they fit well on the board.

And now for the most important part: the sound. It’s a treat to listen with just your ears. I really enjoy working without the distraction of colorful EQ curves.
The highs are addictive. I have to keep reining myself in. With vocals and acoustic guitar, you reach your goal very quickly and put a smile on the musicians’ faces during recording.

Grade 
Stefan
 07/05/2022

my 2nd DIY-Module

This Module was my 2nd DIY build. After I learnd my lesson on my 1st build, what it means to organise all parts befor you start, It was a joy to build this EQ.
And in the end, the most important thing is, this module rocks!!! Compared to my UAD 1073 EQ the EQ curves are very similar and the sonic characteristics are very close, but through the hardware unit, the signal has more body, is more 3 dimensional. I really love this peace of gear. Next thing is building the MP573 an run the EQ through it...Thank you Jean-Pierre for these beautiful kits.

Grade 
Matthias
 11/23/2018

Perfect! The classic Neve EQ and very musical

This EQ needs a lot of patience and concentration while building it, but it is absolutely worth the effort. It’s the perfect supplement for the MP573 preamp. I use it in my studio for tracking on every single track. It’s so musical that you rarely need any other EQs with more bands. If the sound is allowed to get coloured in a nice way you can even use it for mastering – I did this and achieved great results in no time (faster than with a Pultec). It’s great that the EQ573 combines the 1073 and 1084 models: You have a bandwidth switch for the mid frequencies and more frequencies available for the high shelf. It’s worth looking at the frequency response while using it (with Waves Q-Clone for instance) – you begin to understand why you don’t need more EQ bands for a perfect sound ;-)
I disagree with the other reviewer here: I don’t find it harsh at all (if you use it "correctly"). But as always, you should also consider using it for cutting the frequencies you don’t need and not only for boosting. With a reasonable combination you have a high class musical sound and lots of possibilities.

Grade 
ZMFG
 08/01/2018

Good For Certain Things

For the record, I had never soldered before I bought my first Sound Skulptor kit (CP5176). Also, I am not a trained recording engineer. This is the only Sound Skulptor I would give a 4 (out of 6 I own). What I've noticed after using this for a little over a year is that it can be a bit harsh. I use it more for HF/LF cut, and gentle tuning in the inner frequencies. I run it "inside" of my MP573 (which I love!), and occassionally in series when I am not getting the results I'm looking for. The build is a little tricky getting the pots and set up straight, but I had a lot of fun learning how this parametric structure works.

Write your review

EQ573-II Equaliser for the series 500

The EQ573-II is an parametric equalizer based on the design that was originally used in the Neve 1073 and 1084 modules, that has been adapted to the '500' format of API*.

Write your review

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