[sdiy] Reality versus simulation?

Sarah Thompson plodger at gmail.com
Fri Nov 27 16:05:33 CET 2015


Another possibility would be stray capacitance from the breadboard itself causing loss at higher frequencies. Also, are you using a X1 or a X10 scope probe? If you are using X1, this might be the culprit, though 20kHz is a bit low to start seeing much difference there.

As an experiment, try putting opamps before, after and between the stages just configured as voltage followers. This will greatly reduce the distance any high impedance signals need to travel, and tends to make filter weirdness go away. I'm not necessarily suggesting this for a production version, but sometimes going for overkill then backing off is less pain. 

Sarah

Sent from my iPad

> On Nov 27, 2015, at 5:30 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
> As per schematic, +/-10% for the caps, +/-1% for the resistors.
> 
> Values wobbling about would shift the cutoff points a bit, but shouldn't give the significant downhill slope I'm actually seeing. Should it?
> 
> For example, RC variations give me a lowpass cutoff of supposedly 28.4KHz, but actually 25.6 kHz – 31.9 kHz.
> 
> 
>> On 27 Nov 2015, at 11:52, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>> 
>> Tom,
>> 
>>> So what's going on with the real-life filters? Can I improve their performance?
>> 
>> What are the actual values of the capacitors and resistors in your circuit?
>> 
>> Neil
> 
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