Bark Scanning Filter PCB FH / band pass / high pass

Motivation

Bark Scanning Filter PCB FH front view.

This PCB is part of my Bark Scanning Filter project. You can find more information on the Bark Scanning Filter project page

This PCB holds the twenty third and twenty fourth Bark filter. The last band pass with 10500Hz center frequency and the high pass with 13500Hz cut off frequency. It holds the associated VCA's and the associated precision full wave rectifiers as well. For understanding how everything works together please have a look at the block diagram on the project page.



Specs and features



Implementation

Schematic

Bark Scanning Filter 110 FH schemaic 01

Bark Scanning Filter: PCB 110-FH schematic 01

Bark Scanning Filter 101 B1 schemaic 02

Bark Scanning Filter: PCB 110-FH schematic 02

Description:

On page one you can see Bark Filter twenty three, the band pass with 10500Hz center frequency, the precision full wave rectifier for the envelope and the VCA. On page two you can see Bark Filter twenty four the high pass with 10500Hz cut off frequency, the precision full wave rectifier for the envelope and the VCA.


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Calibration

I highly recommend to calibrate all filters before putting everything together. It is much easier this way.

Bark Scanning Filter calibration

Bark Scanning Filter: Filter calibration

First power the filter up. It should draw a quiescent current around 30mA each rail. You can see how I made the power connection on the lower right corner in the picture above.

  • Filter output amplitude
    • Apply a sine of the nominal filter frequency with 0.6Vpp to the input (odd or even).
    • Measure the filter output with an oscilloscope (odd or even).
    • Adjust trimmer TR_1(TR_4) for the output to 5Vpp.
  • Envelope follower output voltage
    • Set the jumper to pre VCA position (odd or even).
    • Measure the ENV output with voltage meter or scope (odd or even).
    • Adjust trimmer TR_2(TR_5) for the output to 5V DC.
  • OTA (VCA) offset)
    • Connect a low current LED with a 5k6 resistor from GND to Iabc input (odd or even). Watch the polarity.
    • The LED should lit up brightly.
    • Watch the signal from the VCA output with an oscilloscope (odd or even).
    • The signal should be the same as at the filter output (odd or even).
    • Remove the input signal.
    • Adjust trimmer TR_3(TR_6) for the output to 0V offset.
  • Modulation test
    • Apply a sine of the nominal filter frequency with 0.6VPP to the input (odd or even).
    • Connect a low current LED with a 5k6 resistor from Iabc input to Iabc output (odd or even). Watch the polarity.
    • The LED should dimly lit.
    • Watch the signal from the VCA output with an oscilloscope (odd or even).
    • Apply a slowly moving voltage at the scanner input (odd or even).
    • The amplitude of the output voltage on the VCA should follow the slow moving signal (odd or even).
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Building hints

  • None

Special parts

  • Replace the CA3280 with the now available AS3280.

Download

Bark Scanning Filter PCB FH documentation download
Bark Scanning Filter PCB FH Gerber files download

Bark Scanning Filter PCB FH front view

Bark Scanning Filter: PCB FH front view


2024 October

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