Maybe best to temporarily remove the top boost module and get the amp running perfect without it. Top boosts are often quite poorly built. The chassis grounds look like they haven't been cleaned. You could unscrew them and clean the contact points with wire wool, then tighten every bolt on the chassis. I've read Steven Grosvenor (AC30 tech book guy) adds an aluminium L shape plate between the power transformer and pre amp to also help reduce hum quite a bit.
I actually find it pretty dang quiet with the top boost out of circuit / in the other channels. Certainly similar to my other vintage amps. I need to do a deep dive on the TB card implementation, I kept everything the same as it was when I bought the amp but who knows if the previous guy did it right. Supposedly it was Mark Sampson of Matchless that installed it way back but who knows.
Hello. I have the exact same vox as you with external top boost but original from factory. on the brilliant channel I have a really strong hum especially when the bass potentiometer goes above half. I'm trying to understand by following your videos how you solved it and where I should check first. the normal and vibrato channels do not have this type of problem. Hope you can help me Thank you
Don't know what program you're using to edit your audio/video, but you should be able to find RTA plug ins or RTA functionality to an EQ plug in. These perform FFT analysis (amplitude vs frequency) on the audio. You should be able to see a reduction of the amplitude at 60hz on the after. You can hear it too. You won't get rid of hiss with this mod. Just mains frequency 60Hz hum. Do this analysis for yourself to visually confirm the difference made by the change. Also find a frequency generator program on your phone. Hook up decent headphones and dial in 60Hz (hum). Then 120Hz (ripple). Internalize this difference so you know that you're listening for.
Old saying: "For every complex problem, there is a simple solution ---- and it's always wrong"! Perhaps not "always", I'm inclined to say "often"; but anyway, trusting those old, greasy, oxidized bolts and nuts, and the oxized chassis underneath them, as "ground" is certain to be problematic.
@@YeatzeeGuitar , there's no substitute for removing the bolt and cleaning the chassis around the bolthole, and either thoroughly cleaning and wire brushing the bolt and nut, adding star washers, or simply replacing the hardware with stainless. Having the socket mounting flange in the middle of the stacked "sandwich" ground doesn't help either (I prefer a dedicated ground). I'm not a Vox expert, but I'd clean all those grounds, every one, with new hardware installed. Perhaps Lyle will give you some tips as to which of those ground points should be relocated...
Well, I know what’s coming next, but semi-spoiler: this did lower heater noise but revealed a different problem…
That's a LOT of hiss; hard to hear hum through the rushing water noise!
Goodbye heater hum, hello ground loops!
Maybe best to temporarily remove the top boost module and get the amp running perfect without it. Top boosts are often quite poorly built. The chassis grounds look like they haven't been cleaned. You could unscrew them and clean the contact points with wire wool, then tighten every bolt on the chassis. I've read Steven Grosvenor (AC30 tech book guy) adds an aluminium L shape plate between the power transformer and pre amp to also help reduce hum quite a bit.
I actually find it pretty dang quiet with the top boost out of circuit / in the other channels. Certainly similar to my other vintage amps. I need to do a deep dive on the TB card implementation, I kept everything the same as it was when I bought the amp but who knows if the previous guy did it right. Supposedly it was Mark Sampson of Matchless that installed it way back but who knows.
Hello. I have the exact same vox as you with external top boost but original from factory. on the brilliant channel I have a really strong hum especially when the bass potentiometer goes above half. I'm trying to understand by following your videos how you solved it and where I should check first. the normal and vibrato channels do not have this type of problem. Hope you can help me
Thank you
Haven't solved it yet, will be circling back to the amp soon so subscribe to catch the video when I do
Don't know what program you're using to edit your audio/video, but you should be able to find RTA plug ins or RTA functionality to an EQ plug in. These perform FFT analysis (amplitude vs frequency) on the audio. You should be able to see a reduction of the amplitude at 60hz on the after. You can hear it too. You won't get rid of hiss with this mod. Just mains frequency 60Hz hum.
Do this analysis for yourself to visually confirm the difference made by the change. Also find a frequency generator program on your phone. Hook up decent headphones and dial in 60Hz (hum). Then 120Hz (ripple). Internalize this difference so you know that you're listening for.
Old saying: "For every complex problem, there is a simple solution ---- and it's always wrong"! Perhaps not "always", I'm inclined to say "often"; but anyway, trusting those old, greasy, oxidized bolts and nuts, and the oxized chassis underneath them, as "ground" is certain to be problematic.
Yeah not a ton of options on the upper chassis, I did tighten that bolt holding the tab for ground to try and help.
@@YeatzeeGuitar , there's no substitute for removing the bolt and cleaning the chassis around the bolthole, and either thoroughly cleaning and wire brushing the bolt and nut, adding star washers, or simply replacing the hardware with stainless. Having the socket mounting flange in the middle of the stacked "sandwich" ground doesn't help either (I prefer a dedicated ground). I'm not a Vox expert, but I'd clean all those grounds, every one, with new hardware installed. Perhaps Lyle will give you some tips as to which of those ground points should be relocated...