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TOILmodular / FUJIN

A "wind/noise"-type Eurorack module with selectable noise types, selectable filters, VCA, and 2 output channels.
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Issue with noise generator #1

Open guytaylor opened 1 month ago

guytaylor commented 1 month ago

Hi there, I just built a Fujin, and am having an issue with the noise section. (Everything else is working fine, ie. VCA, filter, etc) So I stripped it back as much as possible, i.e. I removed all chips apart from IC3 and ran it without the control board and recorded the output I was getting at pin 1 of IC3.

It's sounding like this: https://www.dropbox.com/scl/fi/sfqwj9quzfhejqoxxgds8/Fujin-noise.mp3

Which I assume is not correct. :) Are there any requirements for the Q5? MMBT3904. I just used one I had, or should anyone do? Thanks! :)

TOILmodular commented 1 month ago

Hello Guy. I listened to your recording. Not sure if the noise generator is really the issue here. In general, as far as I know (also not really an electronics expert), each transistor acts a bit differently. But I never had any issues with all my noise circuits. Concerning your recording, I compared it with what I hear at my module's IC3 pin 1. I do not know how you connected to your pin. But if you do not make sure that your recording side is connected to the same ground, as the Fuji module, you might get this low frequency humming sound. I used another output module and just listened via headphone to the output. As long as the two modules were in separate cases, I got the same hum. I then just connected one of the CV inputs from Fuji to any connection in the case with the output module via a patch cable. With that the humming sound disappeared. If you listen closely to your recording, you will hear another white noise mixed together with the humming sound. But the amplitude of that noise is very small. That's because the noise coming directly from the MMBT3904 is very weak. So the next op amp in IC3 with pin 7 as the output is amplifying that noise. Check the output at pin 7. Even with the humming sound, you will get a much louder white noise. You can check the different noise types at the points in the schematic labeled WN_M (white noise, 4th pin from top at the upper left 5-pin connector between main and Ctrl board), PN_M (pink noise, 3rd pin at same connector), BN_M (blue noise, 5th pin at same connector). If you get proper noise outputs there, the issue might be somewhere else. Cheers, Daniel

guytaylor commented 1 month ago

Hi Daniel, Sorry about the long delay in getting back to you :)

I followed your suggestion of recording the output of pin 7, and ground connected. Sadly, it seems to be worse! :) I tried two different power supplies, the first a switched one, the second a linear supply. You can hear it here.

Here is the recording of the both: https://www.dropbox.com/scl/fi/jbfhq3ukhtyjpcwaq39vv/issue-2.wav?rlkey=61f4xtbm1qmgt2w7ec7r3wrnx&st=nivay7uj&dl=0

And like last time this is just the main board (no control) and the only chip I have in there IC3 which should be isolating the just the basic noise source, I assume?

As I have 5 PCB from when I had them made, I might try and build another main board and use a different transistor batch for the noise source. That's about all I can think of at this point.

(I have had issues with previous builds with noise transistors... and needed to try many different ones to get one it working correctly. Not sure if this is a common issue. It will be tricky to change on your board as it's SMD so close to other parts!)

Thanks again Guy

TOILmodular commented 1 week ago

Hi Guy. No worries. I was also on vacation. Let me know if you still have trouble. Maybe we can find out more. Cheers, Daniel