I noticed you're using 0603 resistors in highish values (>10k). Are these bog-standard thick film types or low noise thin film? If the former, they're a major noise source in my experience, particularly at lower frequencies.
I know you now think it's the tone control that is the issue, but there is still an issue with your crossover. Not noise related but distortion related. The top right op-amp appears to be loaded with approx 1k ohm. This is way too low especially as I can't see what it's driving. The minimum load for a TL07 op-amp should be 2k.
Also, on your line out, 2.2k is way too high output resistor. It will introduce noise and signal loss. 100 ohms would be fine to protect against capacitive cables.
Also, on your line out, 2.2k is way too high output resistor. It will introduce noise and signal loss. 100 ohms would be fine to protect against capacitive cables.
Line level filter
I'm stuggling with the design of the filter circuit. How did you arrive at the values you used? The top (high pass) section has a Fc of ~2900Hz for the 1st section on ~2000Hz for the 2nd and both sections are underdamped. The response will have ~2.3dB peak at 3.5kHz.
The LPF section Fc is ~2150Hz but is 2 pole where your HPF is 4. LPF section is also underdamped and the pole on the output of opamp (1.5K and 220N) will cause a 8dB droop between 200Hz and 2kHz.
What response are you targeting (Butterworth, Ellipitic, Cheby, LR) and what is corner frequency?
I'm stuggling with the design of the filter circuit. How did you arrive at the values you used? The top (high pass) section has a Fc of ~2900Hz for the 1st section on ~2000Hz for the 2nd and both sections are underdamped. The response will have ~2.3dB peak at 3.5kHz.
The LPF section Fc is ~2150Hz but is 2 pole where your HPF is 4. LPF section is also underdamped and the pole on the output of opamp (1.5K and 220N) will cause a 8dB droop between 200Hz and 2kHz.
What response are you targeting (Butterworth, Ellipitic, Cheby, LR) and what is corner frequency?
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