Perhaps the reason you don't encounter cascaded real poles is because the transfer function is not very desirable, as most beginner filter designers discover after doing that.Gold wrote:Or you could think of it as an over damped 3 pole filter. I don't think I've ever heard one. Getting perfect three pole filter response by cascading sections isn't what this box is about. This will be tuned by ear in design and use. I also don't think it will end up exactly like I imagined it would. I have never run across anything remotely like what I am proposing although the building blocks are straight forward. I have wanted this box for a long time. I don't imagine a designer would think of doing this as it would appeal to a very limited few. A lot of people seem to want tone boxes that are easy to use. I hate that. I wouldn't let a pultec clone in the same building.JR. wrote: -6db/oct filters are real poles so have fixed Q. Cascading 3 one pole filters tuned for the same -3dB point would by definition be -9dB at tuning (ASSuming you put buffers between them to eliminate loading).
For example cascading three real or natural poles in series tuned for the same -3dB @ say 50Hz, they would add to -9dB at tuning. Further it would be -3dB or half-power up at 2x tuning (100Hz). It would even be -0.3 dB at 10x 500 Hz. Not only that but cascading three passive poles without buffers will result in interaction between the pole tuning due to higher source impedance of previous stages.
In this type of specialty design if it sounds good it is good. As long as this is what you actually want, go for it, but there is a reason you probably won't find these filter alignments in professional products.
JR