Woo audio wa33 hum

Hey all,

Just received my WA33 yesterday. It’s a used model that I was told works perfectly.
It hums like crazy, video available here: https://photos.app.goo.gl/GhybDDYwDcb78aeD8

I know tube amps are much more susceptible to the environment and such but was wondering what would be the best way to troubleshoot the source?


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I’m so sorry! I’d try this out and if you can’t get it to stop, reach out to woo. This is from the site.

22: What to do when my amplifier developed a light hum/noise?

Noises can come from many different places. e.g. power source, audio cables, environmental EMI. To test, please try the following.

  • disconnect all cables from the amplifier.

  • install ALL stock tubes.

  • move amplifier to another area of the house. e.g. living room, kitchen countertop, office, etc. (This is important to isolate the amplifier from other components).

  • keep cell phones, WiFi routers, powered hard drives and other high EMI devices away from the amplifier.

  • connect AC power cord directly to a wall outlet (no conditioners or power strips).

  • connect headphones to the amplifier and set volume to 11 o’clock position.

  • listen through headphone. Do you still hear the hum?

If you still hear the hum, try a ground-lift adapter (for testing ONLY). If the hum goes away using the adapter, you have a ground-loop issue in the house. You can use a device called HUM-X.


Does the wa33 use torodal power transformers? Cause if so those will hum like that when there is a dc offset