# Vox AC30 problem



## Bobbie G (Jan 31, 2018)

Recently I picked up an AC30CC1 in a trade. There is a problem with it that I've never seen before. Sometimes when I turn it on there is very little sound, like barely audible. That is, until I crank it and it jumps in, frightening every one in the room! Once it wakes up it's fine for the night. 

I've tried swapping all tubes except the rectifier. 

Any help is appreciated 🙂


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## Thunderboy1975 (Sep 12, 2013)

Plug in to the effects loop. Any change?


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## Alan Small (Dec 30, 2019)

clean the tube sockets including the rectifier if you have not already done so and spray the pots...the volume pot may have dust that prevents good contact until you turn it enough to get the "wham!" you are experiencing


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## Latole (Aug 11, 2020)

+1 for Alan Small answer.
Bad solder/ contact on power supply rail.
Bad contact on FX loop jacks ( Send / Return)

Turn all volume / gain knobs at least 20 times 0 to to10. With chance it clean volume contact/ wiper . Amp at OFF


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## knight_yyz (Mar 14, 2015)

Sounds like a bad/dirty volume pot


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## Latole (Aug 11, 2020)

knight_yyz said:


> Sounds like a bad/dirty volume pot


Right or bad contact with printed circuit ?


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## Bobbie G (Jan 31, 2018)

I doubt it's the volume pot, I've made it do aerobics without crackling or sound. What fires it up is playing hard and cranking the volume, while master is at max.

I will clean all the connections, pots, sockets, switches.


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## Latole (Aug 11, 2020)

It could be a bad solder somewhere in printed circuit.

FX loop jack contacts ; sometimes it is the issue, you can't clean them
The Send and Return connect the preamp to the power amp by internal contacts to the jacks
.
Put a patch cable ( pedal / guitar cable ) between them. If amp work well, replace jacks.
Patch cable bypass bad contacts.


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## Paul Running (Apr 12, 2020)

Did you try what was suggested in post #2? If you still have the same issue, using the effects loop as an input then most likely the problem is the PI / output side of the amp...the split-method for troubleshooting. The first thing you should check is the power supply...verify that the power supply voltages are stable, this applies to any electronic gear as a flakey power supply can send you off on a wild goose chase.


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## Alan Small (Dec 30, 2019)

just in case ...this trouble shooting is always done with all your pedals and tuner removed from the signal chain


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## Bobbie G (Jan 31, 2018)

Yup, did some testing. Amp works fine when effect loop is turned off, problem returns when turned back on. Cleaned the switch, problem seems to be gone!


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## Bobbie G (Jan 31, 2018)

On further digging I see a mod on screen resistors, does this look ok? Solder joints look ok.


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## nonreverb (Sep 19, 2006)

Bobbie G said:


> On further digging I see a mod on screen resistors, does this look ok? Solder joints look ok.
> View attachment 358157


I'd re-do the solder on those screen resistors. Looks like they're wrapped but not well soldered on the board terminals.


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## loudtubeamps (Feb 2, 2012)

Not familiar with this one so have to ask...are there any relays in the audio path?
That’s my wild guess .


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## Paul Running (Apr 12, 2020)

The screen-grids are operating with 10KΩ stoppers...well protected however, limiting the dynamic range of the EL84s...1KΩ would be sufficient and probably open her up a bit...unless I'm reading it from the opposite end then, it's 820Ω which is tickity-boo.






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## dtsaudio (Apr 15, 2009)

Paul Running said:


> The screen-grids are operating with 10KΩ stoppers...well protected however, limiting the dynamic range of the EL84s...1KΩ would be sufficient and probably open her up a bit...unless I'm reading it from the opposite end then, it's 820Ω which is tickity-boo.


They're 820 ohm 1%. Notice the slightly larger gap between bands on that last brown.
Interesting the schematic shows 100 ohm 1/2 watt. They are clearly 2 watt. And they are original. Not soldered particularly well, but original.


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