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Scratchy rattling resonance
Scratchy rattling resonance
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Old 17th September 2013, 09:07 AM   #11
JingleJoe is offline JingleJoe
diyAudio Member
Join Date: Sep 2013
I had to sign up just to reply to this thread because I was dealing with this exact problem in a filter I built recently!

The resonance in my filter is acheived by adding feedback at a certain point in the signal path which increases Q factor and morphs the filter type into chebyshev, if your circuit is in any regard similar to this we may have had the exact same problem!
Although I can't tell for sure without a schematic.

The problem was that I was overdriving the amplifier portion of the filter. The waveform was hitting the rails and this caused no resonance to happen. Additionally when the input waveform peak to peak voltage exceeded the voltage fed back, less resonance happened. This was due to feedback limitation acheived with diodes.
Basically it's all down to overdriving your resonant parts.

When things were on the edge of resonance attenuation due to overdriving, it got really rattly and scratchy just as you described! I've adapted my filter to encorporate this- it's a feature now, not a bug
Things also got pretty raw when I had some offset voltage fluctuations in a previous design. Sometimes a signal present would cause certain parts of the circuit to become biased up, resulting in the waveform hitting the rails again and loosing resonance and getting all rattly. This happens especially when the input waveform has unequal high and low portions.

To overcome it, I simply attenuated the input signal a lot and amplified the output. This was fine for my specification and didn't even use that many more components but I can see how it would be undesireable for many applications.
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Old 17th September 2013, 09:12 AM   #12
JingleJoe is offline JingleJoe
diyAudio Member
Join Date: Sep 2013

Last edited by JingleJoe; 17th September 2013 at 09:20 AM. Reason: double post! sorry :s
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