Sorry if this has been discussed previously. I am currently building my x0xb0x kit from Willzyx ( great service
) and I have just finished building the VCF and I'm now testing it with my scope. All seem's ok thankfully, but I'm a little confused over the section on the "official VCF tuning" section. I'm building each section and testing as I go along so I want to get this correct.
I have set the controls as mentioned in the fab manual and applied 3.0VDC via R90, and I'm probing VR4 pin next to C13. I can see the waveform on my scope changing with turning controls etc, but turning TM3 gets me no-where near the stated resonant frequency of 500 Hz.
When I do turn it the waveform changes, but the frequency does not ( I have even tried this on a calibrated frequency counter ). Am I missing something here?
I understand that it also mentions that this tuning can be carried out when the whole build is complete, maybe that is best? Is it then just a case of measuring the mix/headphone out frequency and trimming TM3?
Any help/pointers would be greatly appreciated.