Vox AC10 Hissing/Buzzing/Gargling

[DMcough]

So I got a Vox AC10C1 (Tan edition - although that shouldn't make a difference) back in February and almost immediately had an issue with what I can best describe as a gargling sound when I play. It's a lot more noticeable when the bass is cranked and when I play an E note/chord. Took it to a local luthier and he said he'd fixed it (He said he found some loose gaskets) but the buzz came back pretty quickly. Was wondering if anyone else has had this kind of issue on their amps, and if so, what did you do?

Here's a recording of the noise:
https://youtu.be/cZE5knEq6OI

[xtian]

Sounds like a microphonic tube to me, but could be anything mechanical inside the amp. If you plug a speaker into the External Speaker jack on back, does it silence the internal speaker? That'd be the first thing I'd try.

[DMcough]

Sounds like a microphonic tube to me, but could be anything mechanical inside the amp. If you plug a speaker into the External Speaker jack on back, does it silence the internal speaker? That'd be the first thing I'd try.

It does, and the buzzing still continues.

[xtian]

If I understand you--you've plugged in an external cabinet, so the internal speaker is not sounding, and you still hear the noise. That points even more toward a microphonic tube, but also leaves room for bad filtering.

My go-to troubleshooting device for buzzes and rattles is a simple sine wave generator on my smart phone. I use a 1/8" stereo to 1/4" mono cable to play the sine wave into the guitar input. Adjust the frequency and amplitude until you can reliably hear the bad noise in the amp. Now your hands are free to investigate. You can press on the cabinet/speaker/components to find mechanical issues, and you can press on the tubes to see if you can silence microphonic rattling. Finally, you can clip in additional filtering caps at B+ and B+1 to see if that solves the noise.