Audio filter test & measurement with the 2204A - PART 3

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Glovisol
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Audio filter test & measurement with the 2204A - PART 3

Post by Glovisol » Fri Jun 15, 2018 11:44 am

Audio filter test & measurement with Picoscope & 2204A – PART 3

The audio processor to be tested consists of two active, Sallen & Key filters in cascade, a lowpass filter with a corner frequency of 3000 Hz and a specified attenuation of -35 dB at 6000 Hz, followed by a highpass filter with a corner frequency at 300 Hz and a specified attenuation of -35 dB at 150 Hz. The lowpass prototype used for both fiters is a Butterworth 6th order. All filter details, including individual section Q factors, are shown in the schematic uploaded in Part 1.

Figure 1 shows pass band up to 3 KHz and attenuation in the range 0 - 300 Hz. Picoscope parameters used are:
- Y Axis scale 3.00
- Balance 3%

Figure 2 shows initial pass band up to 6 KHz. Note this is an initial response with slope to be compensated by means of R5.2, as shown in Figure 3 following. Also note this is a very early test with light/50 Hz feedthru to the zener still present and you can see this by the responses at 50 Hz and multiples.

Figure 3 shows compensated pass band up to 6 KHz. Picoscope parameters used are:
- Y Axis scale 3.00
- Balance 5.33%

Figure 4 shows pass band up to 12 KHz.Picoscope parameters used are:
- Y Axis scale 3.00
- Balance 3%

Figure 5 shows pass band up to 24 KHz.Picoscope parameters used are:
- Y Axis scale 3.00
- Balance 2%

Filter attenuation should increase monotonically for a few more octaves, but as a limit to the display we have the instrumentation's dynamic range which imposes a constant lower floor to the measurement, as shown in all figures.
Attachments
Complete breadboard.JPG
Pss band  to 3 KHz.jpg
Figure 1 - Pass band to 3 KHz
Pass band to 6 KHz with slope.jpg
Figure 2 - Pass band to 6 Kz (initial response)
Pass band to 6 KHz.jpg
Figure 3 - Pass band to 6 KHz - corrected slope
Pass band to 12 KHz.jpg
Figure 4 - Pass band to 12 KHz
Pass band to 24 KHz.jpg
Figure 5 - Pass band to 24 KHz

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