My Vox VT30 has suddenly started humming and not in a good way.
I have been reading about others having this issue but have not found the fix yet.
Here's my scenario:
1. Amp has a hum like a 60hz ground loop after turning it on and with the volume control in the back of the amp all the way off.
2. Lifted the ground and no change.
3. Tried different AC outlets and no change.
4. Reset the amp holding Channel 1 and 4 buttons down, turning it on and then pressing Bypass.  This resets the digital brain and there was no change.
5. Sent an email to Sweetwater Support to see if they know anything about this.
6.  Ordered a new tube today which I will get right after Christmas.
 
When I first got the amp, it was really quiet.  I have barely used it in this last year.  It cost $200 and I don't think I want to spend $100 getting it fixed so I posted this thread so see if anyone has any clue as to what might be going on.
I would love to get this amp working again.
TIA
Rimshot

Don't forget, Sweetwater doubles the warranty...
 

Yes but I am out of warranty now...

Sounds like a bad power supply capacitor, but solid state is mysterious to me. It may be worth a visual inspection to see if there's any obviously blow components. Just be careful not to touch anything lest the static blows it up.

Hi John.  I will check that out.  Thanks much for the tip.
In your experience, could this issue be related to a bad tube?  I am concerned that there is hum even when the master volume control is turned all the way off.  
 
Thanks.
 

It depends where the master volume is located in the circuit. I thought it was a Solid State amp. If it has tubes and uses an AC heater voltage (6.3 volts) then you could have an imbalance in the heater supply. With that AC supply they balance the AC with a grounded center tap to cancel hum. Many transformers today don't have a center tap to save money. Instead, they connect each side of the heater supply to ground using a resistor. This creates a balance and cancels hum. If a resistor goes off spec or gets a bad connection, then it can cause noise.
 
I don't think I explained that too well, but I've got the flu and a spinning head. Try changing the tube and see if the hum goes away. The reason that the volume doesn't affect the hum level, is that the hum is being generated at a point past the volume control or outside of the signal path completely. 

ampfixer
It depends where the master volume is located in the circuit. I thought it was a Solid State amp.

I've had little luck finding a schematic, but it looks like it has a solid state front end and tube output.
 
Rimshot, if you don't know what you're doing, I wouldn't go sticking my hands into your amp, on or off.  There are voltages around 400v, sometimes stored in large capacitors that aren't automatically leaked when you turn off the system.
 
Changing a tube shouldn't be a problem if you can get at it without touching anything else.  Not sure you'd be getting any sound if there was a problem with an output tube, which I think is all you have.  How many tubes to you see?  Just two big ones, two big ones and a small one, or some other combination ?
 
 

I wouldn't suspect a tube.  That sounds more like a power supply (capacitor) problem.
 
I don't know about Vox, but many amps use connectors internally to connect, for example the preamp board to the power amp board.  If that connector is not making good contact it can cause hum.  Peavey was famous for internal connector problems on amps that use Molex connectors. 

I see just one tube.  It is a 
Electro-Harmonix 12AX7EH Preamp TubeThe volume control is located on the back of the amp.  
Here is some help on the subject:
http://www.valvetronix.net/forums/vt30-problem-loud-hum-t4484.html
 

Look at the good news: at least it's not a bad output transformer.