Hi All. I hope this topic fits this room. I have a custom amp based on the AC30 with 2 Celestion Alnicos. The amp has less than 10 hours use on it. It sat for a year or two without using, and I know I am supposed to use a variac to power it up, but I turned it on, loud pop, and now one of the speakers is buzzing like it's blown. When I put my hand on the cone the buzzing/grumbling stops. This amp was never cranked. Did I blow the speaker? Hold downs are all tight, and I cant see anything rattling, though I have not checked tubes yet. Thank you in advance. Also, I'm assuming that I cannot simply unhook one speaker and run it, as this will damage the transformer?
Sincerely,
toneless in Seattle
Sincerely,
toneless in Seattle
Depending on the year this is a good website for downloading VOX amps including the VOX AC30 -
Vox Vintage Circuit Diagrams
Circuit depends on the year of manufacture .
Vox Vintage Circuit Diagrams
Circuit depends on the year of manufacture .
I see that this is your first post, inboil.
You say that this is a custom combo based on the AC30. Can you give more details or photos of the speaker connections?
You ask if it is OK to 'unhook one speaker'.
You can certainly run the amplifier with one speaker in order to check its operation. The amp will not be upset by the change in impedance in the short term. Just don't accidentally play through the amp when no speaker load is connected.
However, we really have to ascertain the reason for that loud pop which appears to have totally stressed out the now buzzing loudspeaker!
You say that this is a custom combo based on the AC30. Can you give more details or photos of the speaker connections?
You ask if it is OK to 'unhook one speaker'.
You can certainly run the amplifier with one speaker in order to check its operation. The amp will not be upset by the change in impedance in the short term. Just don't accidentally play through the amp when no speaker load is connected.
However, we really have to ascertain the reason for that loud pop which appears to have totally stressed out the now buzzing loudspeaker!
If the speaker is buzzing then the AC current is activating the voice coil it means the speaker is basically working , having repaired speaker voice coils its possible it has overheated causing the coil to come into contact with the surrounding magnet generating a scraping noise .
That doesn't matter at this stage it sounds like a tube or component relating to them has either blown or short circuited but as Galu has rightly said whether the other speaker is either okay or has completely blown resulting in silence ?
Tubes develop short circuits internally and EL84,s are no exception especially after long use as a guitar amp.
That doesn't matter at this stage it sounds like a tube or component relating to them has either blown or short circuited but as Galu has rightly said whether the other speaker is either okay or has completely blown resulting in silence ?
Tubes develop short circuits internally and EL84,s are no exception especially after long use as a guitar amp.
Thank you for the replies. I will get some pics of the speakers this evening. I will de-solder one lead of the suspect speaker and see if that stops the noise. The other speaker is working, so as Galu suggested, I will play with that one only for a while.
The loud pop only happened the one time after the amp sat for over a year. Last night it did not pop. Could that have really blown one speaker?
The loud pop only happened the one time after the amp sat for over a year. Last night it did not pop. Could that have really blown one speaker?
It is unlikely the speaker voice coil was damaged unless there was a large surge in current. The other speaker may just have been lucky to survive!
You didn't turn the amp on when the volume control was turned up full by any chance?
Re de-soldering one lead of the suspect speaker. If the speakers are in series, you will completely unload the amp - bad idea! Only do that if you know for certain the speakers are connected in parallel.
If you are uncertain, wait till your photos reveal the layout of the speaker wiring.
You didn't turn the amp on when the volume control was turned up full by any chance?
Re de-soldering one lead of the suspect speaker. If the speakers are in series, you will completely unload the amp - bad idea! Only do that if you know for certain the speakers are connected in parallel.
If you are uncertain, wait till your photos reveal the layout of the speaker wiring.
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Thank you for that tip. With a multimeter, what should I look for as a reading, if I unhook one? I would at least like to play it for a few seconds to determine if the speaker is bad, as they are 300$ a piece. OUch!
Well, I assume its like any circuit. Positive of one to neg of the other would be series.
Well, I assume its like any circuit. Positive of one to neg of the other would be series.
So, I de-soldered the negative lead of the suspect speaker but then had no sound at all, so, I soldered it back. When I press the cone, the rattling goes away, and when I lay the amp on its face, the rattling also goes away. Also, as the amp warms up, the noise lessens. So, I am hoping it's not the speaker. But I anxiously await your replies. Thanks in advance.
You've been advised not to unsolder one speaker until you've made sure whether they're connected in series (as in a stock AC30) or in parallel. You did it anyway. No sound means that both speakers in fact are in series. Hence, desoldering one of them means no load for a tube amplifier, which is bad. You might have destroyed something else in your amplifier during operating it without load.
Sorry, I'm afraid we can't successfully help you if you don't obey basic advices, in other words: don't know what you're doing.
Best regards!
Sorry, I'm afraid we can't successfully help you if you don't obey basic advices, in other words: don't know what you're doing.
Best regards!
De-solder the negative lead from the amp as before. Set your multimeter to the low resistance (ohms) setting and place the probes across each of the speakers in turn.
The speaker that buzzed will probably measure around 6 ohm, since its voice coil is not actually broken.
The other speaker will read around 6 ohm if it is OK, but you will get no reading (infinite resistance) if the voice coil is broken.
Report back your findings along with photos for further advice. N.B. Do NOT turn on your amp again until you are sure it has a safe speaker load.
I thought if the speakers were in series, I'd be ok. I only ran it for a minute before shutting it off. Once reconnected, it worked normally. As mentioned, the noised seemed to totally go away when the amp was face down, and the rumbling decreased significantly as it warmed up, which makes me hope something is loose. Why would a speaker perform differently if rotated 90 degrees? Thanks again for all the help in solving this. You have been very supportive.
If you've got a rubbing voice coil, you might cure it by rotating the speaker. It's just a matter of gravitational force that gets the VC centering optimized this way.
Btw, I've often read suggestions to rotate especially big woofers with heavy cones and VC's every year or so to keep them performing perfectly. But I've never followed it
.
Best regards!
Btw, I've often read suggestions to rotate especially big woofers with heavy cones and VC's every year or so to keep them performing perfectly. But I've never followed it
.Best regards!
I know you don't want to contemplate it, but the 'buzzing' speaker certainly has a damaged voice coil. As Kay says, changing the orientation of the speaker, as in laying the amp on its face, will change the extent to which it buzzes.
If there was a fault in the amplifier, it would affect both speakers equally.
If there was a fault in the amplifier, it would affect both speakers equally.
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Apart from a damaged voice coil, other causes of speaker 'rattle' are:
If you are not familiar with the parts of a loudspeaker, then refer to the attached diagram.
- The paper cone can separate from the speaker basket. Make sure the cone is firmly stuck down all around its circumference.
- The dust cap can separate from the centre of the paper cone.
- The corrugated disc (the spider), which supports the rear of the paper cone near the magnet, can separate from the cone or the speaker basket.
If you are not familiar with the parts of a loudspeaker, then refer to the attached diagram.
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