# Vox AD30VT - cutting out ?



## bagpipe (Sep 19, 2006)

I've read about people having reliability issues with these Vox Valvetronix series amps, but mine has been fine .. until now ! 

The amp will be working fine and then the output just dies away. It looks like a power amp issue as there is absolutely no sound coming from the speaker, even with all the controls dimed. If I toggle the power switch it usually brings everything back again .. until the next time that it cuts out again. 

I took it apart and reseated all the connecters etc but I cant see anything obvious wrong. Is there a known culprit for these kind of issues on these amps? I guess this is the reason that people stick to good old fashioned point-to-point wired tube amps.


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## greco (Jul 15, 2007)

bagpipe said:


> If I toggle the power switch it usually brings everything back again .. until the next time that it cuts out again.


Do you think that the power switch itself could be making and breaking contact somehow? Probably unlikely...just a thought. Switches would typically be an " all or nothing" sort of thing.....but I've seen situations where that has not been the case.

Good Luck with it

Dave


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## bagpipe (Sep 19, 2006)

greco said:


> Do you think that the power switch itself could be making and breaking contact somehow? Probably unlikely...just a thought. Switches would typically be an " all or nothing" sort of thing.....but I've seen situations where that has not been the case.
> 
> Good Luck with it
> 
> Dave


Dave, thanks for the suggestion, but the power remains on to the amp - the LEDs on the control panel are still lit when theres no output.


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## Wild Bill (May 3, 2006)

bagpipe said:


> Dave, thanks for the suggestion, but the power remains on to the amp - the LEDs on the control panel are still lit when theres no output.


Hey BP!

I'm not aware of any common fault with these amps. Inside there's not a lot besides on big module and some glue parts around it, if I recall. The module has a thermal cutout which shuts it down if it gets too hot. Maybe that's an issue.

Anytime I'm chasing an intermittent cutout problem that starts working when you toggle the power switch my first suspect is a coupling capacitor. Caps often can open up and flicking the voltage on and off will make it "heal" but still be weak enough to keep failing.

Anyhow, as you've probably noticed when you look inside, electronic parts rarely make it obvious that they've conked out by looking fried from the outside. Rather they look just perfectly fine even though they're snackered in their innards! That's why we need test meters. A tech will take measurements and then say: "That reading's totally mental! Now what would cause that?"

Even when you find a bad part you don't simply replace it. You also have to ask yourself why the heck it failed! Something blew it and if you just tack in a new one it's likely that one will just blow too.

I guess the short answer is, you need a tech!:smile:

:food-smiley-004:


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## nonreverb (Sep 19, 2006)

I've worked on several similar amps and many times it's a solder problem. Sometimes during production, the wave soldering machine goes a little too fast under the board and the joints are thin...add a few hours of heat 'n cold and what do you get? Yup, cracked solder joints. I'm not sayin that this is the problem for certain but it is worth checking...particularly around connectors and the power amp transistors themselves:smile:


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## Ripper (Jul 1, 2006)

I've fixed a couple of these. One was solder joints, the other was simply a memory reset. If you check out some of the vox forums you'll find this is a common problem with this series. The memory chip doesn't always clear itself so you need to do a factory reset to get this working. You'll lose your settings but it worked. The following is from the vox manual

1. Turn off the power

2. While holding down both the CH and WRITE buttons, turn the power on.
When the CH1 and CH2 LEDs begin blinking, release these two buttons.
HINT: If you decide to abort this operation, press the TAP switch at this point.

3. When you press the WRITE switch, the CH1 and CH2 LEDs will change from
blinking to lit. Initialization will be completed in a few seconds, and the amp
will switch to Preset mode.
NOTE: Never turn off the power while initialization is taking place.


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## bagpipe (Sep 19, 2006)

Ripper and Nonreverb, thanks for the good suggestions. I was suspicious that it was a cold solder joint, and was trying to wiggle connectors, slightly bend the circuit board etc to try and force the failure, but I couldnt do it. I may take the main power board off and visually inspect it for a bad joint. I took the amp out of the cabinet and currently have it sitting on top of the amp. I left it powered on for 24 hours in case it was something heat related? Since doing that, I havent seen the issue, but it may just re-appear when I put the amp back into the cabinet.

I'm going to try the factory reset tonight. Thanks for providing the instructions.


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