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
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.
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.
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!