I'm going to set C3 filter at ~800hz.
I think adding back some low mids and cutting some lows with C4 may get me where I want to be. A little more beef and less honk.
RAT - What's with these filters?
- Thread starter jwin615
- Start date
I think adding back some low mids and cutting some lows with C4 may get me where I want to be. A little more beef and less honk.
YourGuitarist
New member
The LM308 in this configuration does not invert. Some op-amps do invert once voltage swing reaches rails such as the TL072. Its notable that the R3/5 & C2/3 are not true hi passes as the non-inverting configuration has a minimum gain of 1 so the LF blocking behavior of the caps acts like a shelving filter.
As for the other stages, a lot of builders specify their filters outside of the audio range because there is attenuation approaching the -3dB that stacks when multiple filters are used. This is especially true for first order filters as are most commonly used in pedals. The effective system corner frequency rises with successive filters.
Also the inversion might just be the cumulative phase shift from the filters, each one contributing 90 deg individually.
In other words, several 1st order hi passes at Fc=10Hz will produce a total hi pass with say an Fc=~20Hz etc.
Just for reference.
As for the other stages, a lot of builders specify their filters outside of the audio range because there is attenuation approaching the -3dB that stacks when multiple filters are used. This is especially true for first order filters as are most commonly used in pedals. The effective system corner frequency rises with successive filters.
Also the inversion might just be the cumulative phase shift from the filters, each one contributing 90 deg individually.
In other words, several 1st order hi passes at Fc=10Hz will produce a total hi pass with say an Fc=~20Hz etc.
Just for reference.
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YourGuitarist
New member
Here's a graph of input response, it seems I *may* be wrong concerning the low / high passing attenuating below unity in the op-amp. The HF shelving effect is however visible. A pole (low pass) is formed by the gain pot and and C3 in the sim. That pole moves down in frequency as gain increases. This stacks with the famous slew rate limiting too (which is not modelled here). V1 is the input filtering. V2 is the op-amp output.
Note that FR changes with gain so you may be able to get different sounds by hitting the front of the pedal harder and keeping the gain control lower.
Note that FR changes with gain so you may be able to get different sounds by hitting the front of the pedal harder and keeping the gain control lower.
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