MFOS State Variable VCF Noise / Output Level Issue [solved]

[roglok]

I need your help guys. I just powered up my MFOS 12dB VCF - everything works, but there are two issues:

1. The output level is very low

2. The circuit injects a considerable amount of white noise somewhere before the actual filter (i.e. the LPF can remove it completely)

I bet those issues are related, but I'm a noob and don't know where to start bugtracking. I've checked the board for any cold solder joints and swapped some of the op-amps to no avail.

Any ideas?
Thanks!

[roglok]

Please, somebody help me. I've managed to build the Steiner Synthacon VCF and other circuits on stripboard without any problems - now I'm working on my first professional PCB for the modular and it's driving me nuts!

The debugging so far involved switching to a +/-15v PSU, swapping all ICs and checking resistor values, but I can't get rid of the bloody noise. It's not static or ground loop hum, but a rather musical type of noise. I can make a recording if that helps... Could it be related to a bad cap? I've used film capacitors for the 0.1µF bypass caps and WIMA FKP for the integrators.

I'm grateful for any suggestions.

[haxster]

The Noise Level whistle is normal. Mine has that too. I have built several and all have that noise in one form or another.

As for the Signals being too low. You want to change the Input resistors from 1M to something like 100k-470K. 1M makes it sound too low.

[roglok]

Thanks for the clarification, haxster!

I figured the "low volume" was due to my input signal not being hot enough. Since the resonance level does not change with gain, the signal level was low in comparison to the oscillating filter. With a signal around +/-5V, the levels are just fine.

I wonder why Ray, given the excellent explanation on his projects, has not mentioned the noise issue at all. If it's a feature, I can live with it. Just thought something's wrong there...