Debugging my mission filter board

Hi Everybody, Hi Oliver,
After my first build with standard filter and the second with a ladder filter I hoped the mission would be straight forward as well, unfortunately it doesn’t work out of the box for me, I have to get into debugging…

Digital board is done and works allright, I can access all pages and have the filter set to 4pm. It receives midi notes and shows it.
Nevertheless, I hear only a clicking sound with every note that comes through, and I am not able to tune the filter.

I was checking the unfiltered Osc signal, that seems to be ok. Changes as well when I change a patch.

Now at this point I am stuck - what points do I need to probe on the filter board to follow the signal path, and Identify if I have a fried component or a short or a bad solder point somewhere?

Thanks for any support,

As pictures help most of the time, here is my mission build:

Do you have the additional 6 pin header installed (not reqired for the standard filter)?

Yes, both headers are installed and connected. Does that link work ok with the pictures?

The build instructions show 4 points corresponding to each fitler stage. Have you tried listening to them?

Just checked, point 1 and 2 have a very faint audio signal, point 3 and 4 seem silent, no signal at all

What about IC1 pin 1?

Has Osc signal, far more level as the pins around IC5 for the filter stages

Photo of your board?

Does that link in my 2nd post work? Ok, it didn’t work for some reason, please copy n paste the URL…

The link works when cut n pasted, but clicking it doesn’t. You have a few dry joints it seems. Hard to tell which without a more sideward view.

I added two more pictures with a more angled perspective. You think resoldering might be an easy option to eliminate this potential fault? I tried to use little solder to keep the nice white PCB nice white…

I didn’t see your link.

Soldering looks OK.

Voltage on IC2 pin 7 with cutoff set to 0? Then with cutoff set to 127?

I read 1,86V with cutoff = 0 and -0,11V with cutoff =127

This is correct.

Resolder all pins of IC5, IC4, IC6.

Did so (resoldering sockets, and passive components around it), reseated IC 4, 5 and 6.

I think the behaviour is still the same, when I tried to figure out what it is I realised that changing the settings on envelope 2 changed the clicking sound when a new note is triggered, i.e. setting attack to more than 30 made it basically fade out, and either decay or sustain need to have a value to have that click hearable. I think it is the envelope of the VCA that is hearable on its own/ on the base noise.

any other idea? would it help to record the sound it makes?

The filter doesn’t work.

It probably outputs a steady voltage (clipping from one of the op-amps?), and what you hear is the VCA envelope multiplied by this constant voltage. It doesn’t indicate a malfunction of the VCA.

Fix the filter first.

So you confirm you have clear signal on IC1 pin 1; but crap on IC4 pin 1? Do you have a scope?

Good morning,
I don’t have a scope yet, just ordered an usb scope, hope it’ll be here by tomorrow. In the meantime I can try to use the scope plugin on my DAW. What do I need to measure with the scope?

What is the best way to verify that IC5, V2164D is not fried?

Thank you,

The scope plugin on your DAW won’t work. Doesn’t measure DC, doesn’t give voltage.

> What is the best way to verify that IC5, V2164D is not fried?

If it gets extremely hot, that is a bad sign. Otherwise, the only way to know is to put a chip known to work…

I was afraid, regading the scope, that the simple means would not be good enough ( I assume that rules out the simple smartphone - mic - osc out as well).

The chip is not getting hot, I can’t feel any temperature difference to the other chips on the board.

I verified the signal again, following the schematics:
IC1 Pin 1 is ok
IC5 Pin 2 is ok (slightly less volume)
IC4 Pin 2 and Pin 1 is barely hearable, I need to crank up the gain quite fully to hear something, but the signal is basically there.

To me it looks like the Filter is not opening, I think I will check the voltages on IC5 pin 3 as well, maybe the connection between IC2 Pin 7 and and IC5 pin 3 is broken?