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Ampeg SVT-CL Crackling Sound (video)

#21
shaggy45 said:
How I figured out it was a bad preamp tube in mine was to bypass the preamp and see if it still made the crackle. It didn’t so that narrowed it down to the preamp. I snatched the preamp tubes out of my blues jr and put those in and no problems. So I ordered new ones and it’s been great ever since.
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But was it the 12AX7/AU7 in the preamp that you pull out of the front of the amp, or the preamp tubes that are actually on the chassis itself next to the power tubes?
 
#24
Ok, just had a good long while to test a bunch of different things. The problem is back with a vengeance. Turned the amp on for about 45 min playing through it at band volumes straight in. Bass > Cable > Amp. Everything seemed to be working fine. Tapped on all of the tubes (preamp, driver, and power tubes) and got no strange sounds.

Then, plugged in my pedalboard. Tuner > Compressor > Fuzz > Preamp. The crazy broken up sound immediately started. I double check to make sure it wasn't any of my pedals causing the issue, so I checked all the patch cables and everything seemed fine so I plugged directly back into the amp again and the sound was still there now, like the increased volume from the pedalboard had shaken something up causing this issue to happen.

I just tried wiggling the input jack on the 0db and 15db inputs and it's crackling loudly when I do that. Thinking those solder joints might be bad. I'm going to reflow the solder there and check it again in a few.
 
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#25
zwish said:
Ok, just had a good long while to test a bunch of different things. The problem is back with a vengeance. Turned the amp on for about 45 min playing through it at band volumes straight in. Bass > Cable > Amp. Everything seemed to be working fine. Tapped on all of the tubes (preamp, driver, and power tubes) and got no strange sounds.

Then, plugged in my pedalboard. Tuner > Compressor > Fuzz > Preamp. The crazy broken up sound immediately started. I double check to make sure it wasn't any of my pedals causing the issue, so I checked all the patch cables and everything seemed fine so I plugged directly back into the amp again and the sound was still there now, like the increased volume from the pedalboard had shaken something up causing this issue to happen.

I just tried wiggling the input jack on the 0db and 15db inputs and it's crackling loudly when I do that. Thinking those solder joints might be bad. I'm going to reflow the solder there and check it again in a few.
Click to expand...
Could very well be the problem. Wonder why none of us thought to tell you to check that. We must be slipping :D
 
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#28
Resurrecting this thread because I’ve encountered an almost identical-sounding issue. Seems to crackle badly but only on the low G note.

Swapped the 12AX7s in the pre-amp section for news ones - noise still occurs exactly the same as before. Strangely, it seems to happen when the head is on top of the cab but not when it’s on the floor. Suggest to me there may be something loose somewhere and it’s being vibrated but hard to know where. I suspect it’s in the pre-amp section because I ran an XLR from the balanced output and the crackle came through the PA too.

Has anyone come across this before?
 
#29
andykeating said:
Resurrecting this thread because I’ve encountered an almost identical-sounding issue. Seems to crackle badly but only on the low G note.

Swapped the 12AX7s in the pre-amp section for news ones - noise still occurs exactly the same as before. Strangely, it seems to happen when the head is on top of the cab but not when it’s on the floor. Suggest to me there may be something loose somewhere and it’s being vibrated but hard to know where. I suspect it’s in the pre-amp section because I ran an XLR from the balanced output and the crackle came through the PA too.

Has anyone come across this before?
Click to expand...
For me, it ended up being the input jacks themselves. I resoldered both the 0db and -15db inputs and that cured it. Try putting a little sideways pressure on the instrument cable in the jack when the noise is occurring to see if you can make it happen.
 
#30
andykeating said:
Resurrecting this thread because I’ve encountered an almost identical-sounding issue. Seems to crackle badly but only on the low G note.

Swapped the 12AX7s in the pre-amp section for news ones - noise still occurs exactly the same as before. Strangely, it seems to happen when the head is on top of the cab but not when it’s on the floor. Suggest to me there may be something loose somewhere and it’s being vibrated but hard to know where. I suspect it’s in the pre-amp section because I ran an XLR from the balanced output and the crackle came through the PA too.

Has anyone come across this before?
Click to expand...

Isolate the source. Send the preamp out signal to another amp, if you hear the static there, more than likely, it is in the preamp.

Reseat all the connectors in the preamp. After swapping out the tubes, try retensioning the tube sockets.
 
#31
Quick update - seemed to have sorted it. Reseated the tubes and made sure the pre-amp tray was secured really tightly when I screwed it back in. Shone my torch in via the back to make sure all the screws went in properly.

It had recently been in the repair shop for some resoldering to the heating plates because it was taking a while to warm up properly. So I suspect something may have not been screwed back in properly and the vibrations from the G note were shaking things somewhere inside.

Tested it continuously for about 45 minutes after, which was the longest I’ve had to noodle for a while, and the problem didn’t reoccur. :cigar:
 
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