Collosalus - background noise issue (not heterodyning) - Solved

[JerS]

Hi gang, I am really stumped with this one. Here is the issue:
- I can hear a pronounced "swooshing" sound and loud hiss when not playing. The guitar is nicely flanged when playing, but this noise is excessive.
- I built two boards at the same time, one has the issue, the other does not (it is acceptably quiet)
- I cannot dial it out using the trimpots without losing the flange effect on the guitar

What have I done to try and fix:
- all voltages appear correct against the reference in the documentation
- I have replaced the MN3007 chip with several others (5 in total) - all have the same issue, and all work fine in the other board.
- I have replaced the NE5332 opamp, did not fix the issue
- I replaced IC4, the 4049 and 4013 chips, did not fix it.
- audio probed to try and find the source of the noise but could not pinpoint it. All I know is that the excessive hiss is present on pin7 of IC4 and also at pin 7 of the MN3007 and follows through to the output. This noise is not present on the other board I built.
- tried running with 12v power. Issue persists.

I built board using 1n5817 diodes and 100uf cap, no heterodyning noise (I have built several of these boards and know what that can sound like). I did not make any other parts subs, and all parts came from the same "batch" as far as I can tell as I ordered the lot at the same time.

If anyone has any idea where I can start looking to try and solve this I would be appreciative. I really need to salvage this board as there are none left available in the store!

Thanks - Jer

[JerS]

Well...I guess sometimes what you need to do is take a break and have a coffee. I have been working to try and solve this issue for 2 days, and posted here as a last resort. After posting I had a cup of coffee and decided to audio probe the power nets on the board. In a comparison, the noisy board was...well noisier. So long story short - I replaced the regulator and voila! Problem solved. Maybe it was a bad component, I dont know. I dont care now!

Sorry to have wasted your time with my ramblings! Hopefully this helps someone else.

[blearyeyes]

After reading your first post it seemed that the only thing left was the Charge pump circuit injecting noise somehow.....Then I read your next post.
Thanks for posting. I didn't know that could happen.

[Jeremy]

BlearyEyes, you make a good point - I should have mentioned that I changed the charge pump chip also, and it did not cure the problem. It was definitely the regulator. I noticed a few posts where folks described a similar issue, but then the post would gravitate toward solving the heterodyne issue.

I wanted to record this issue so that other searchers would have something else to check!