Crackling Sound From AC30

[Pink Unicorn Horsey]

Just this morning, I started getting a crackling sound from my AC30. The best way I can describe it is like playing with a bad patch cable—the sound never cuts out altogether, but jumps from normal to quieter, then back to normal, as though you were jiggling the plug of a bad cable in your guitar jack.

(BTW, I've ruled out a bad cable or bad guitar output jack, as this happens with any cable and any guitar I use. I'm getting this whether I plug into the Brilliant or Normal channel.)

Any ideas?

- Keith

 

[CaughtLikeFire]

Re: Crackling Sound From AC30

Just this morning, I started getting a crackling sound from my AC30. The best way I can describe it is like playing with a bad patch cable—the sound never cuts out altogether, but jumps from normal to quieter, then back to normal, as though you were jiggling the plug of a bad cable in your guitar jack.

(BTW, I've ruled out a bad cable or bad guitar output jack, as this happens with any cable and any guitar I use. I'm getting this whether I plug into the Brilliant or Normal channel.)

Any ideas?

- Keith

nice avatar

try some tube swapping - crackling is usually preamp tubes.

1st pull each one, make sure the contacts are clean, and reinstall them. I use a dot of dielectric grease.

if the contacts are all good, take a good 12AX7 and try swapping it into each position to find the culprit.

 

[Pink Unicorn Horsey]

Re: Crackling Sound From AC30

nice avatar

Thanks. I found it on the IntarWebs.

try some tube swapping - crackling is usually preamp tubes.

1st pull each one, make sure the contacts are clean, and reinstall them. I use a dot of dielectric grease.

if the contacts are all good, take a good 12AX7 and try swapping it into each position to find the culprit.

I've never serviced this amp before myself, so I'm a bit clueless what I should and (more importantly) should NOT be touching. I opened up the back panel and found a big-ass circuit board, but no easy way to get at the tubes.

- Keith

 

[That90'sGuy]

Re: Crackling Sound From AC30

nice avatar

try some tube swapping - crackling is usually preamp tubes.

1st pull each one, make sure the contacts are clean, and reinstall them. I use a dot of dielectric grease.

if the contacts are all good, take a good 12AX7 and try swapping it into each position to find the culprit.

Yep, go for the preamp tubes first

 

[glassman]

Re: Crackling Sound From AC30

Keith,

Remove the chassis from the cab and lay it on a table with newspaper spread out on it, tubes facing up.

Go to Radio Shack and pick up a small can of DeOxit.

Remove each tube, one at a time and spray a little squirt of the DeOxit in the socket. Immediately place the tube back in and rock it gently. If the sheild mount is too tight to rock it, remove and reinsert several times.

Repeat for each tube except the rectifier tube (the one with the larger, octal base. For it, just squirt and reinsert; don't rock it as you can break off the index pin.

If the sound is still there, swap out a different 12AX7 to see if they are the problem. Hint: if the level of the "sound" can be attenuated with the volume control, the problem tube would be either the phase inverter or one of the power tubes.

A power tube on the verge of shorting can make a popping sound. If it is a power tube problem, I wouldn't use it until you have installed a new quad.

 

[J Moose]

Re: Crackling Sound From AC30

I've never serviced this amp before myself, so I'm a bit clueless what I should and (more importantly) should NOT be touching. I opened up the back panel and found a big-ass circuit board, but no easy way to get at the tubes.

That's because the tubes are BEHIND the circuit board on the back side of the chassis... pointing at the front wall of the amp, above the speakers.

If you look at the bottom of that picture, those four white circles are the power tube sockets. Rectifier tube socket is on the right, same row. Preamp tubes are just above those.

To get at them you need to remove the whole "head" portion. There's four bolts holding it in place, two on each side. Lay the amp on its face (speakers down) and pull those bolts out with a #3 phillips... #2 is too small. Has to be a #3 or you'll strip them. Ask me how I know that... hehe

But yank those four bolts and you'll be able to lift the whole chassis out and gain access to the tubes. There are, IIRC... a half-dozen 12ax7s and one tube is something else... I can't recall... but its for the trem circuit. Not a "standard" tube but not hard to find.

What I'd recommend doing while you troubleshoot the amp is to make a long speaker cable so you can separate the chassis from the cab and facilitate changing tubes easily w/o having to go through the whole mounting/unmounting process because it SUCKS and you'll likely have to do it several times.

Its worth it to replace that stock, crap speaker cable with something heavier in any case. I made the business end of mine long enough that I could feed a different head into the Vox speakers, or mainly... to use an attenuator.

The AC30 is really, really hard on tubes... and if you run yours where I like to run mine (channels jumped, volumes up around 2pm) its even harder! I've heard several techs call the AC30 an easy bake oven for tubes and it really fits.

Noises in these can be notoriously hard to track down... I have the exact same amp and almost every time I've had an issue it was tube related. But I've never had the crackling noise...

How old are the tubes and how hard do you run the thing?

Before you run off to the Shack for contact cleaner, do you have a multi-meter? How about a clip to drain the voltage? 5 or 10 watt resistor, some wire and alligator clips to drain the voltage and make it "safe" to probe around.

Get some chopsticks too...

 

[Pink Unicorn Horsey]

Re: Crackling Sound From AC30

I'll bet it is a bad pre-amp tube. I've had this amp for about five years, using it intermittently but often running it with the volume closer to 4:00 or 5:00 (read: nearly dimed).

The idea of getting a gazillion-volt shock from this amp scares the hell out of me. Even just draining the voltage, I'd want to have someone watching me who knows what he's doing. Anyone want to stop by this afternoon and give me a hand? There's a cold six-pack with your name on it if you do.

- Keith

 

[d1dsj]

Re: Crackling Sound From AC30

I had this with my Cornford MK just last week.... I think I've sorted it. I traced it to a bad solder connection on the footswitch! I would guess at a bad connection/ dry joint somewhere although I hope yours is just a valve. Good luck.

 

[\m/(00)\m/]

Re: Crackling Sound From AC30

i never really look at names...so the avatar had me convinced you were Zerb... and i thought "what the heck is Zerberus doing with an AC30?"

 

[J Moose]

Re: Crackling Sound From AC30

I'll bet it is a bad pre-amp tube. I've had this amp for about five years, using it intermittently but often running it with the volume closer to 4:00 or 5:00 (read: nearly dimed).

Sweet!!!

In that case I'd suggest a new set of power tubes... especially if you bought it used with old tubes.

I've had fairly good luck with the JJ's. There's some 'better' sounding tubes out there for sure, but there's a trade off with durability. Sovteks are NOT recommended and prone to quick failure & random noises IME. Haven't tried the EH power tubes yet.

When I was using my AC30 often, couple days a week I'd burn though a set of power tubes a year.

FWIW - I had a problem last year with mine where the amp would go full-tilt open... loud 60hz buzz at full blast, pretty randomly but consistently every time I used it. Didn't matter where the volume was. Could be after 30 seconds or 30 minutes of playing... I'd power cycle the amp and it was fine... for another 3 minutes.

Turned out to be a bad preamp tube which I only discovered after having the thing opened up on my bench & probing around with chopsticks for a week, thinking it was vibrations or a bad solder joint, cap etc.

I pulled the preamp tubes for use in other amps and one of 'em failed almost immediately. After that I put the whole thing back together and its been great.

If I lived closer I'd for sure stop over & help. I could probably even walk you through most of the guts over the phone...

But honestly, if you aren't even comfortable draining the voltage off the caps which is easy, then put the back lid on & stick to tube changes or haul it in for service.

I'd try the tubes though... and maybe some contact cleaner in the pots.

 

[Thurisaz]

Re: Crackling Sound From AC30

Is it possible you didn't play this amp in 6 months to a year? Guitar World's Matt Bruck says that if you 'shock' the amp with too much voltage too quick, it'll end up making nasty popping sounds and what not when you dig in with the pick. There's a little more to it than that, but that's the basic of it.

 

[J Moose]

Re: Crackling Sound From AC30

A power tube on the verge of shorting can make a popping sound. If it is a power tube problem, I wouldn't use it until you have installed a new quad.

What's the chance of a bad screen resistor, or one that's going bad?

 

[Pink Unicorn Horsey]

Re: Crackling Sound From AC30

But honestly, if you aren't even comfortable draining the voltage off the caps which is easy, then put the back lid on & stick to tube changes or haul it in for service.

I'd try the tubes though... and maybe some contact cleaner in the pots.

Thanks, Moose (and the rest of you). Helpful stuff.

I think the pots definitely could use some contact cleaner.

As for just taking care of the tubes, I still need to remove the whole chassis, correct?

 

[Pink Unicorn Horsey]

Re: Crackling Sound From AC30

Is it possible you didn't play this amp in 6 months to a year? Guitar World's Matt Bruck says that if you 'shock' the amp with too much voltage too quick, it'll end up making nasty popping sounds and what not when you dig in with the pick. There's a little more to it than that, but that's the basic of it.

Good question! However, I think the longest it went without being played is a couple months.

 

[J Moose]

Re: Crackling Sound From AC30

As for just taking care of the tubes, I still need to remove the whole chassis, correct?

Oh yeah. Only way to get at 'em is to pull the chassis.

If you look through the top vents you can actually see the tubes... especially when its on & lit up. And if you reach around the back, above the speakers... you'll feel a metal plate running the length of the chassis. The tubes are behind that.

If the pots are scratchy/noisy when you turn them they need to be cleaned. Sometimes... often, just giving them a full rotation about a dozen times is enough to clean the muck.

 

[the guy who invented fire]

Re: Crackling Sound From AC30

You have to pull the chassis in an AC-30 to get to the tubes and due the bone headed design of AC-30's they are known to eat tubes...I'd say new tubes all around is a good first stop...if the noise keeps up after that find a good amp tech and have it looked at.

 

[kevlar3000]

Re: Crackling Sound From AC30

Clean all your input jacks, speaker and FX loop jacks along with the tube sockets. I have had this happen with more than one amp, simply due to the higher humidity of summer. Sometimes it is that simple... Cords and speaker cables good? ....

 

[Pink Unicorn Horsey]

Re: Crackling Sound From AC30

Clean all your input jacks, speaker and FX loop jacks along with the tube sockets. I have had this happen with more than one amp, simply due to the higher humidity of summer. Sometimes it is that simple... Cords and speaker cables good? ....

Cord's good. It's a combo, so no (external) speaker cable.

 

[auxjoel]

Re: Crackling Sound From AC30

I currently have a similar problem, when I use overdrive pedals, or crank the amp's own gain, I get crackle noise on some notes, it's not a constant sound, but just when I strum some notes. It causes this 2nd layer of crackly/speaker fizzle type sound that sits on top of the expected overdriven sound. I replaced all the tubes with brand new ones. and it is still happening. I also ran via an external speaker, and it still happens then too (not using the built in speaker).
I am running a VOX ac30cc2 (which has the 'link' ability that lets you run Top Boost and Normal channel together via 1 input)
I tried Normal, Top Boost, Top Boost+Normal(using the link option)
I tried the Warm and Hot setting on the back of the amp. and I also tried the Classic and Modern setting on back of the amp. But in all cases the crackle is still there.
Any ideas?

 

[beaubrummels]

Re: Crackling Sound From AC30

If it’s a glassy sheen kind of buzz that is more related, my black AC30 does that because I have a microphonic V1 tube. Using a short plate tube in V1 is supposed to fix it. Not my #1 amp so I haven’t bothered.