Vox Valvetronix VT30 Cutting Out

[almano]

Hi, I hope the following is of some help to others who have experienced their “Valvetronic” Vox VT30 amp cutting out for no reason.

It is a bit of a long story, but please bear with it - it should all make sense in the end (I hope!)

I bought one of these amps about 3 weeks ago, as I thought it would be a good, self contained practice amp for Shad’s sounds all from one box. After just a few days I kept finding the amp would crackle and pop – and sometimes it wouldn’t even produce any sound at all from the guitar unless the jack was pulled in and out of the amp several times. At first I wondered if it was anything I was doing that was wrong – so I checked out several forums on the ‘net. It seems this is a (very) common problem with this amp! The general reply to this problem from the Vox moderators is to liberally douse the sockets and pots with switch cleaner – the reason being that oxidisation occurred in storage. Now this is strange, because my old Fender amp, after decades of storage and no maintenance at all, worked first time when I plugged it in a couple of months ago – no bangs, whistles, pops or humming – just good plain clean guitar. If oxidisation was the reason, surely an old neglected Fender amp would be the one to display problems, not a brand new Vox amp!

Anyway, although I knew it would invalidate any warranty, I thought I would take the thing apart and investigate why the Vox VT30 was behaving so badly.

The common consensus of forum opinion seems to centre around the jack socket – so I thought this would be a good place to start checking. I removed the chassis and found the jack socket soldered into a small circuit board held in place by a single screw and the jack socket fixing itself. There was some metal foil screening ‘covering’ on the copper track side of the board held in place by some double sided padded tape arrangement. I peeled this off so that I could check the solder connections on the jack socket – it all looked okay. It was then that I noticed what appeared to be a DC blocking polyester capacitor in the signal path cemented into more of that metal foil screening. The thought then occurred to me that if this capacitor was dry joint or open circuit, then the fault conditions it would cause would be the very one’s I am experiencing.

Being that this capacitor is a new component, it is most unlikely that the legs/wires of the capacitor would have oxidised so soon. This process normally takes years to happen – and, even then, the flux in the solder would usually sort out that problem in the normal process of assembly. No, there had to be another answer to the problem – I think it all probably boils down to the beige coloured cement compound they use to secure the metal foil screening to the capacitor. I rather think it’s more than likely they apply this cement compound before they solder the capacitor to the input board. My estimation is that solvent from the cement leeches along the legs/wires of the capacitor and causes a bad solder joint of that particular component to the board.

In order to prove my theory correct I used some ‘solder wick’ to remove the old solder, then I carefully scraped the capacitor wires with a scalpel blade and remade the joints with well fluxed solder and a very hot soldering iron.

I reassembled the amp – and, what do you know – it sounded like it always should have done from the beginning! No drops in volume or crackles or even anything untoward – just a nice sounding amp with lots of Shad’s style sounds in one convenient box! I have used it for around 20 hours now, on and off, since the "fix" and it has performed wonderfully - so hopefully this could be an answer to an ongoing problem that has annoyed many users of this amp.

Alright, I will admit that the 24 bit digital processing circuitry can tend to pick up interference from computers and monitors – but that isn’t too intrusive if the amp’s placed in a sort of null spot (moved from here to there until it sounds right!) All in all though, except for this particular ‘cutting out’ Achilles ’ heel, this isn’t a bad piece of practice amplification for the price.

I do hope my own findings with this amp may be of some help to anyone else who experiences a similar problem with their own VT30.

Best of luck with it, but don’t forget to take the usual precautions with soldering and electrics if you are going to have a go yourself.

Cheers,

Alan.