Pro Hard Knee Feed-Forward Compressor

This is an implemental circuit design of a hard knee feed-forward compressor applies a Pre-Trimmed Blackmer ® VCA THAT2180 series. It is designed to have standard professional audio completions such as balanced input/output, input-level potentiometer, and the most common compressor controls such threshold, ratio, attack, and release. It is also designed to have standard compressor function indicators such as input-level indicator and gain reduction indicator.

The Operating Controls

This circuit provides the following standard operating controls:

• Input Level Control

  This input level control allows user for manually setting the input level signal before compressed. Amount of the controlled signal level before compressor can be visually monitored via the input level indicator that has indication steps as -40dBU, -20dBU, -10dBU, -5dBU, 0dBU, +5dBU, +10dBU, and +20dBU.

• Treshold Control

  This threshold control provides the range between -40dBU to +20dBU. This is a hard knee threshold control type.

• Ratio Control

  This ratio control allows user for manually setting the compression ratio. The minimum ratio is 1:1 or by meaning that no compression. The maximum ratio is an infinity ratio or by meaning that it puts the compressor to work as a limiter.

• The Attack Time Control

  This attack time control allows user for manually setting amount of time for this compressor to reach the optimum gain reduction as that set via the threshold and ratio. It provides attack time range from approximately 1 ms to approximately 500 ms.

• The Release Time Control

  This release time control allows user for manually setting amount of time for this compressor to put back the output signal into the original level if the input signal level is decreased in condition that the threshold is lower than the configured input signal level or for reconfiguring the output signal into the proper level to re-follow the threshold and ratio settings. It provides release time range from approximately 5 ms to approximately 1800 ms.

The Indicators

This compressor circuit has two blocks of signal indicator drivers to provide input level indication and gain reduction indication:

• Input Level Indicator

  This indicator allows user for visually monitoring amount of the passed signal level that set via the input level control. It has 8 indicator LEDs those will indicate the step levels as -40dBU, -20dBU, -10dBU, -5dBU, 0dBU, +5dBU, +10dBU, and +20dBU.

• Gain Reduction Indicator

  This indicator allows user for visually monitoring amount of the gain reduction if compression occurs. It has 8 indicator LEDs those provides indication as 1dB, 3dB, 6dB, 9dB, 12dB, 18dB and 20dB.

The Trimming Of RMS Detector

This compressor circuit is designed with adjustable RMS detector. It has a low limit adjustment ("bottom output voltage" adjustment) and a level adjustment. The low limit adjustment as RT1 is used to set the lowest output voltage limit in which usually in approximate to -230 mV. The level adjustment as RT2 is used to set the output level to have the output voltage levels as accurate as possible to the output voltage levels of THAT2252.

Schematic Download

The schematic is freely available for download. It includes the analysis schematic in KiCad EDA V.8x format that can be simulated with use NGSPICE V. 43.

Download URL of the original design source in KiCad EDA format: https://sourceforge.net/projects/analog-audio-signal-processors/files/IMPLEMENTAL/HARD-KNEE-FEED-FORWARD-COMPRESSOR/STD-HKFF-COMPRESSOR-SCH-ONLY.zip/download

Download URL of the schematics in PDF format: https://sourceforge.net/projects/analog-audio-signal-processors/files/IMPLEMENTAL/HARD-KNEE-FEED-FORWARD-COMPRESSOR/STD-HKFF-COMPRESSOR-PROJECT-MAIN_CIRCUIT.pdf/download and https://sourceforge.net/projects/analog-audio-signal-processors/files/IMPLEMENTAL/HARD-KNEE-FEED-FORWARD-COMPRESSOR/STD-HKFF-COMPRESSOR-PROJECT-INDICATOR.pdf/download

PCB Design

The PCB design is available commercially. Feel free to contact the designer by WhatsApp message +62-897-5727-020 to purchase the PCB design files bundle.

If you want a special PCB design for this model, feel free to consult to the designer by WhatsApp direct message.