# PA20 Mixer general crackle noise on all channels

**URL:** <https://forums.allen-heath.com/t/pa20-mixer-general-crackle-noise-on-all-channels/31776>\
**Category:** Other A&H Products\
**Created:** [15 April 2026 15:01 UTC](https://forums.allen-heath.com/t/pa20-mixer-general-crackle-noise-on-all-channels/31776 "2026-04-15T15:01:52Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Mojoampguy](https://avatars.discourse-cdn.com/v4/letter/m/f05b48/32.png) [@Mojoampguy](https://forums.allen-heath.com/u/Mojoampguy)\
**Post date:** [15 April 2026 15:01 UTC](https://forums.allen-heath.com/t/pa20-mixer-general-crackle-noise-on-all-channels/31776/1 "2026-04-15T15:01:52Z")

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Trying to repair a pa20 unpowered mixer for a local charity group. Basic problem is a crackling noise with nothing connected on both Left and Right outputs (shows up on PFL too. I isolated each channel by disconnecting the flat strip main mixing bus, one at at time. Noise still present, so it is not likely coming from a faulty channel. I viewed power supplies for noise on my oscilloscope. +10v supply used on Effects board is very noisy. I replaced all the output side components in the +10v supply circuit ( diode, filtering components, capacitors,resistors, inductor) but see no change. Disconnected the PSU fan just in case it was the source.

note. +/-15v and 48v supplies are noise free.

Questions

1. Is this likely to be the source of my noise problem , like I personally suspect?
2. If not, what else could I attempt to isolate the noise source?
3. Having already replaced all comments in the +10v circuit of the PSU, do you have any suggestions?

Thanks in advance