I've been asked to build a custom stereo 3 band EQ circuit for mastering: 315Hz Low-pass Shelf, 315 to 3.15K Bandpass, 3.15k high-pass shelf. Boost and Cuts on all bands. I've been looking over the Night EQ circuit and it seems simple enough to mod the high shelf frequency, but I'm having trouble wrapping my head around the low shelf and the bandpass. How do I do low-pass shelf with a gyrator circuit like these? How do I do a bandpass? I assume I can chain a low-pass shelf and a high-pass shelf to get a bandpass in this fashion.
Also, I need boost and cut +/-5dB in 1dB increments for each channel using 2-deck 12 position rotary switches so that both channels are controlled by one knob. Is there a formula I can use in this case to calculate resistor values for various dB boosts/cuts? I've looked over the Night EQ threads and I've seen posts about using rotary switches over the rev log 500k pots, but I haven't seen a post about replacement resistor values.
Now that I think about it, if I'm chaining a high-pass into a low-pass to get a bandpass, I'd need to control the boost/cut of the high-pass and low-pass at the same time. For a stereo unit, that would require a 4-deck rotary switch, wouldn't it? Is there a way to control the boost/cut for the bandpass section with a 2-deck rotary?
Sorry for all the questions, but this is my first custom EQ circuit and I'm trying to figure it all out. If there's an easier way to get what I need, I'm all ears. If at all possible, I'd like to avoid a passive design with a makeup gain stage at the end.
The circuit in question:
http://www.khstudio.us/DIY PICs/3D EQ - FULL.bmp
Also, I need boost and cut +/-5dB in 1dB increments for each channel using 2-deck 12 position rotary switches so that both channels are controlled by one knob. Is there a formula I can use in this case to calculate resistor values for various dB boosts/cuts? I've looked over the Night EQ threads and I've seen posts about using rotary switches over the rev log 500k pots, but I haven't seen a post about replacement resistor values.
Now that I think about it, if I'm chaining a high-pass into a low-pass to get a bandpass, I'd need to control the boost/cut of the high-pass and low-pass at the same time. For a stereo unit, that would require a 4-deck rotary switch, wouldn't it? Is there a way to control the boost/cut for the bandpass section with a 2-deck rotary?
Sorry for all the questions, but this is my first custom EQ circuit and I'm trying to figure it all out. If there's an easier way to get what I need, I'm all ears. If at all possible, I'd like to avoid a passive design with a makeup gain stage at the end.
The circuit in question:
http://www.khstudio.us/DIY PICs/3D EQ - FULL.bmp