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Volume goes up by itself

Jay Arnold

Jay Arnold

May 7, 2018
12
4
#1
So I recently purchased a SVT-212av. I am running my Fender Jazz through a Boss gt1B, to a Fender Rumble 500 to the SVT.
The issue is ever since I replaced the cab my volume will increase on its own the more i play. FOH says they are not seeing it on the board but could hear the volume increase. Has anyone ever had this issue??? Please help.
 
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#5
It may be a Pot going bad on the Rumble. The vibration could be causing to let more signal through. That's my my best guess. You could try turning all the pots back and forth a few dozen times or more.
 
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#6
FunkHead said:
It may be a Pot going bad on the Rumble. The vibration could be causing to let more signal through. That's my my best guess. You could try turning all the pots back and forth a few dozen times or more.
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This is extremely unlikely. If the pot hasn’t moved physically, it’s not going to be the cause unless the pot is so noisy that it’s unusable to begin with.

There are multiple dynamics control circuits and solid state switching circuits in the Rumbles, a failure in one of these can cause this, but it’s pretty rare.
 
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#7
agedhorse said:
This is extremely unlikely. If the pot hasn’t moved physically, it’s not going to be the cause unless the pot is so noisy that it’s unusable to begin with.

There are multiple dynamics control circuits and solid state switching circuits in the Rumbles, a failure in one of these can cause this, but it’s pretty rare.
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How about maybe the switching component in the effects loop? Or one of the switches on the front such as bright, contour, vntage or overdrive?

If it was me I would cycle every pot & switch a bunch of times. Especially ones that are seldom used.

I have seen Pots cause this exact problem but maybe they were an older design?
You could just tap on them and they would affect the volume.
 
#14
Having developed a lot of circuits, I have run across odd things from time to time. Oddest one was a signal processor that would work just fine, and after a few hours, stop passing signal. It wasn't thermal, it was a ground issue - an op amp didn't have a reference ground - when it powered up, the bypass capacitors on the supply formed a capacitive voltage divider between the plus and minus rails, so the op amp was biased. As it was a FET input op amp (very low input current) it took about 3 hours until the voltage at its input drifted up to the positive supply, and then it shut off. It was hard as hell to find - if you probed the ground with any sort of scope probe or meter, there was enough conductivity in the test gear to reset the bias for the op amp, and it'd work fine for a few more hours.
 
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#16
micguy said:
Having developed a lot of circuits, I have run across odd things from time to time. Oddest one was a signal processor that would work just fine, and after a few hours, stop passing signal. It wasn't thermal, it was a ground issue - an op amp didn't have a reference ground - when it powered up, the bypass capacitors on the supply formed a capacitive voltage divider between the plus and minus rails, so the op amp was biased. As it was a FET input op amp (very low input current) it took about 3 hours until the voltage at its input drifted up to the positive supply, and then it shut off. It was hard as hell to find - if you probed the ground with any sort of scope probe or meter, there was enough conductivity in the test gear to reset the bias for the op amp, and it'd work fine for a few more hours.
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Fortunately, these don’t occur in production products!
 
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#19
Jay Arnold said:
So I recently purchased a SVT-212av. I am running my Fender Jazz through a Boss gt1B, to a Fender Rumble 500 to the SVT.
The issue is ever since I replaced the cab my volume will increase on its own the more i play. FOH says they are not seeing it on the board but could hear the volume increase. Has anyone ever had this issue??? Please help.
Click to expand...
Hearing sensitvity, and frequency response. Nothing's different, just your perception.
 

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