US$289
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| Discount | -10% | -15% | -20% |
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- Free Shipping for Orders $299+
- Handmade in HRK Workshop
- Fully Assembled and Tested
- Express Delivery to Europe │ USA │ UK │ Canada
- Fully Featured Diode Bridge Compressor
- similar design to Neve's 2254, 2264, 33609
- Adds complex Harmonics and analog warmth
- enhances the sound stage and track content
- Easy-to-Use for beginners
- proffesional studio editing tool
- Threshold from -25dB to +20dB
- Ratio from 1.5:1 to 8:1
- Fast Attack from 250uS to 100mS
- Recovery from 50mS to 2.5S
- +20dB Gain Make-Up
- Side-Chain 160Hz HPF
- Gain reduction meter
- Stereo Coupling Option
- Carefully selected high-Quality components
- Coupled with HRK Active Transformer
- On-Board Voltage 500 Rack PSU Filters
- Soft-Start PSU Function
- Direct Sale - Save on Distributors Fee!
CP554 | Diode Bridge Compressor Introduction and Demo
Video by Adam Steel. For more content visit https://youtube.com/@adamsteelproducer
The Sound of Vintage Transformers
The extensive use of the transformers in the classic diode bridge compressor units designed by Rupert Neve, was dictated by technological limitations of the 60s and 70s.
Simply put, the transformers were the only available devices at the time which could do a specific function in the pro-audio circuitry. For example, matching the input and output impedance, level reduction or amplification, and transforming the signal from balanced to unbalanced or vice versa.
CP554 is designed and built with the use of modern electronic components. Although it follows the classic diode-bridge compressor design principles, it is not a copy nor a clone of any vintage unit. A large number of the transformers in the diode bridge is not a must‐have design requirement! Transformers can be replaced by modern electronic components delivering a better signal to noise ratio and better electromagnetic interference immunity.
In the default mode, the CP554 will provide just a mild amount of the harmonics produced by the diode-bridge circuitry, while being neutral and non‐destructive to the music material.
Why Diode Bridge Compressors are so Rare and Expensive?
There are plenty of studio grade compressors on the market. The most popular are VCA, FET and opto-compressors.
The diode bridge compressors are rather rare and the options are limited. The most obvious are made the AMS-Neve units based on the original Rupert Neve’s designs, the 2254, 2264 and 33609 stereo compressor.
Some manufacturers introduces the Neve’s clones based on the widely available original diagrams. It is important to point, that even the most accurate clone, won’t identical to original, due to the transformers available from Carnhill.
To use the diode-bridge element as the gain control block, the circuitry has to be designed in the specific way. The ideal symmetry of the signal is crucial. In 60s only transformer could deliver close signal symmetry.
The increased noise floor is the other problem of the classic diode-bridge compressors. Improper circuitry design will drastically increase the noise, rendering the compressor unusable for the studio application.
Building the 1:1 copy of the Neve’s compressor is easy, but it is not enough to make a good quality equipment. Only deep insight understanding of the diode-bridge compressor design is the key to success.
CP554 is not a clone! It is designed to fallow the principles of the diode-bridge circuitry and to obtain best possible performance.
The Vinatage Mode
Vintage Mode is a proprietary design by B. Hrk of analog processing circuitry which delivers the same type of transformer harmonics which are present in the classic diode bridge compressors.
Vintage Mode is a fully analog circuitry (No DSP) designed by applying the practical knowledge and understanding of a classic analog circuitry performance, response and behavior. The extensive knowledge of the laws of physics, how the transformers and vintage circuitry work, combined with experience in analog circuitry design, allows to accurately reproduce the same performance, character, vibe or mojo of vintage analog circuitry and transformers. Electronic engineering is a science, not magic!
Vintage Mode circuitry ensures the same type of response of the signal as in the vintage transformers. More signal creates more harmonics. The overall experience is very similar to what any vintage unit would deliver, including the frequency and tonal response.
By default, the CP554 is neutral and versatile. It does not impose any strong character on the music material, vastly increasing the number of studio and music production applications. If required, the vintage mode will introduce classic/vintage harmonics, converting the CP554
to a vintage/classic Diode Bridge Compressor. Therefore, CP554 is 2‐in‐1.
Stereo Buss Operation
- Our improved production process ensures stereo matching between units
- If you purchase two units in one order, both units are matched for stereo operation, bus processing and mastering.
- Spcial stereo coupling link cable is supplied with every pair of CP554
*The Stereo Link cable is provided together with a pair of the CP554.
CP554 | Diode Bridge Compressor vs. DAW Plugins
HRK Active Transformer
Bart Hrk developed the propitiatory design of an Active Transformer to solve the problems of the common passive transformers.
Passive transformers are susceptible to electromagnetic interference (50Hz Hum, RF Smog) and the frequency response is dependent on load and source impedance, negatively influencing the overall performance of analogue studio equipment.
The HRK Active Transformer solves the problems of the passive transformer while preserving and even enhancing the positive trades of the transformer output stage, including the harmonics content and the tonal response.
The HRK Active Transformer delivers the sound that we love, including the harmonics content and the tonal response, and removes all the hassles associated with passive transformers.
The Active Transformer produces a subtle “Air” effect and provides extended LF performance.
The Active Transfomer saturation depends on the output level. Higher output signal levels will saturate the Active Transfomer more, like in the classic studio equipment.
CP554 | Diode Bridge Compressor vs. Dione VCA Compressor
CP554 Specification
| General | ||
| Input Type / Input Impedance | Balanced Electronic | 20k |
| Output Type / Output Impedance | Balanced HRK Active Transformer | Less than 10R |
| Max Output Level | +25dBu@0.1%THD with 1k Load | * Balanced Signal |
| Recommended Load | Balanced 10k | Minimum Supported Load 600R |
| Initial Gain | 0dB | Gain Make-up set to 0dB |
| Phase Reverse | No | CP554 is not introducing phase reverse in any mode of operation. |
| Frequency Response | 5Hz-80kHz@-1dBr | Compressor disengaged. |
| Static Noise Level | -95dBu@10Hz-22kHz | Compressor disengaged. |
| Power Consumption | Typically 45mA per unit | 60mA max. per unit |
| Format | API 500 Format | Compatible with most of the 500 Racks |
| Compressor | ||
| Type of Compressor Engine | Diode-Bridge Symmetric Gain Cell | |
| Compression Curve | Adaptive Soft-Knee | Depends on the Threshold and Ratio knob settings |
| Threshold Range | -25dB / + 20dB | Smooth Continues Potentiometer |
| Ratio Range | 1.5:1 - 8:1 | Smooth Continues Potentiometer |
| Attack Time | 250uS - 100mS | Smooth Continues Potentiometer |
| Recovery Time | 50mS - 2.5S | Smooth Continues Potentiometer |
| Side Chain HPF | 150Hz@6dB/oct | Use the HPF Switch |
| Frequency Response | 5Hz-30kHz@-1dBr | Compressor engaged. |
The input signal should be connected to the rear XLR input.
It is recommended to use -12dBu input signal level initially and increase the level signal if required.
ALL HRK Products Are Brand New - Assembled and Fully Tested
All HRK Products are tested with the industry best audio measuring equipment
Audio Precision System
- Our improved production process ensures stereo matching between units.
- If you purchase two units in one order, you can be sure that both units are matched for stereo operation, bus processing and mastering.
All Items are dispatched from Poland in the European Union within 1-3 working days.
| Country / Region | Shipping Cost | Customs Fee | VAT |
| All 27 European Union Countries Delivery Time: 2-7 Days | – 14.99USD for orders below 299USD- FREE shipping for orders over 299USD | NO Customs Fees | – Yes, for personal orders- Not charged with the EU VAT number |
| United Kingdom Delivery Time: 3-7 Days | – 14.99USD for orders below 299USD- FREE shipping for orders over 299USD | NO Customs Fees | No VAT charge. HMRC collects the VAT. |
| USA, Canada Delivery Time: 5-10 Days | – 14.99USD for orders below 299USD- FREE shipping for orders over 299USD | NO Customs Fees for orders up to 800USD – charged by the USA Customs Office | No VAT charge. |
| Australia Delivery Time: 5-14 Days | – 19.99USD for orders below 399USD- FREE shipping for orders over 399USD | No info available – refer to local regulations. | No VAT charge. |
| Switzerland Delivery Time: 3-7 Days | – 14.99USD for orders below 299USD- FREE shipping for orders over 299USD | No info available – refer to local regulations. | No VAT charge. |
| Norway Delivery Time: 3-7 Days | – 14.99USD for orders below 299USD- FREE shipping for orders over 299USD | No info available – refer to local regulations. | No VAT charge. |
| Russia, Ukraine, Belarus – NOT AVAILABLE | NOT AVAILABLE | NOT AVAILABLE | NOT AVAILABLE |
| Worldwide destinations Delivery Time: 3-14 Days | – 29.99USD | Refer to local regulations. | No VAT charge. |
EU Customers
The EU Customers will not pay any extra customs fees.
Business customers with valid EU VAT number will not pay the 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.
For personal orders from the EU, the VAT will be added at the checkout.
UK Custmers
We ship directly to United Kingdom.
UK VAT tax is collected by HRMC
Non-EU Customers
Customers from outside the EU 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 a custom invoice will be issued.
USA and Canada
Orders from the USA below 800USD are FREE from customs tax.
We ship directly to USA and Canada
Payment Options:
You can pay for your order with any Credit Card and Apple Pay!
7 Days Return Policy
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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