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Ampeg SVT CL - Power Fault on Specific Bass

T

Thing1

Feb 24, 2014
30
1
#1
Hey guys, I have hauled this amp to my amp tech twice and spent $200 but have had no luck. I have a 2005 Ampeg SVT CL that is doing the power fault led flash when using my Mark Hoppus bass through it while driving the amp hard. This ONLY happens when driving the amp hard with that specific bass (around gain 4, master 7). The amp makes a poof sound and fades away then the power led starts flashing. If I use my Ibanez bass everything works just fine.

My amp tech has resaugthered the board and biased the amp. I think the Mark Hoppus bass is driving the amp too hard with the Seymour Duncan Quarter Pound pickups.

Any experts know what might be going on? Is it just a situation where I can roll the bias back a little bit on the back of the amp? I've had this amp for a few months and really want to enjoy it, it's been in the shop for 3/4 of the time.
 
#2
Can you try the same bass on another amp of the same model?

Are you sure your amp is set to the correct impedance?

Are you sure your cabinet is correctly labeled with regards to impedance? Nobody made changes?
 
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#4
Thing1 said:
Hey guys, I have hauled this amp to my amp tech twice and spent $200 but have had no luck. I have a 2005 Ampeg SVT CL that is doing the power fault led flash when using my Mark Hoppus bass through it while driving the amp hard. This ONLY happens when driving the amp hard with that specific bass (around gain 4, master 7). The amp makes a poof sound and fades away then the power led starts flashing. If I use my Ibanez bass everything works just fine.

My amp tech has resaugthered the board and biased the amp. I think the Mark Hoppus bass is driving the amp too hard with the Seymour Duncan Quarter Pound pickups.

Any experts know what might be going on? Is it just a situation where I can roll the bias back a little bit on the back of the amp? I've had this amp for a few months and really want to enjoy it, it's been in the shop for 3/4 of the time.
Click to expand...


AFAIK the fault kicks in under two situations: 1. the line AC voltage is too high, 2. one or more output tubes are pulling dangerous levels of current.

Although conceivably the amp may only shut down with a particular bass, IMHO the problem is still with the amp or output tubes.

Here is a more in-depth post I wrote on how the bias sense and fault circuits works: Svt cl fault
 
#5
Did you try reproducing the fault at the tech's shop? Low power line voltage can cause this. Take a reading of the AC wall voltage where this occurs. If it's below 115VAC it can cause this.

Don't run the amp through a power conditioner.

There are many possibilities. Hopefully the tech checked the power tube cathode resistors.
 
#6
IK Multimedia - AmpliTube SVX

"So accurate, it even shut down
Funny story… during the first phase of testing with the original engineers, one particular software model was being driven so hard that it "shut down." Completely stopped working. But the lead engineer approved the model on the spot. You see, there was a slight design flaw in the actual amplifier that would cause a power fault shutdown if the amp was driven too hard for too long. The software model was so accurate that it even replicated this design flaw! "

Find tech and that know of the design published in the schematic:
Ampeg SVT-CL | Repair
 

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