Very Strange Ampeg SVT Classic Issue

metro_area · #1 06-02-2010, 04:38 PM

I had the weirdest thing happen with my head last night, and I'm wondering if anyone has any input to remedy / repair it:

I'm running a late 80's SVT CL through an Ampeg 610HLF. I've got a tuning pedal, MXR 10 band EQ, volume pedal, and Sonic Maximizer in my signal chain (in that order) and a Fender American P/J Bass.

At practice last night, I turned off my EQ to see what the straight signal would sound like. However, the second I turned the EQ off, everything went completely silent. My bass wasn't making any sound or sending any signal to the head. Instant dead silence. I thought it might be an issue with the pedal, but when I clicked it back on, it was the same issue - silence.

I looked at the head, and the Standby/Power/Fault light was flashing. It was flashing back and forth between Red and Green. I've repaired several SVT's in the past, and know that the flashing means there is an issue. I turned the standby on, then turned the power off. I let it sit for only about 30 seconds, then turned the power back on. 3 minutes later (I usually wait longer, but we were in the middle of practice) I turned the standby off - and the light turned green. No more issues, no more silence, everything worked perfect for the rest of the night. I did not, however, turn any more of my pedals on or off, aside from the tuning pedal which didn't cause any issues.

Does anyone have any idea/guess as to why turning an EQ pedal off would cause my fault light to flash and the SVT to quit working? Obviously, I could just leave my pedals alone, but it's the concept that is concerning. I usually have more pedals (fuzz, delay, etc) in my signal that haven't caused any issues with my previous SVT heads, and I'm afraid once I add the pedals I need to turn on and off during a set back into my signal chain that this will happen again. Maybe during a set, which is obviously a huge concern.

Any input would be amazing!

craig.p · #2 06-02-2010, 07:46 PM

I'm not familiar with that MXR box, but if by "turned off" you mean "powered down," it's possible you sent a huge (as in many volts) DC transient to the input stage. Now, I know there's probably some high-pass filtering going on in the Ampeg preamp, but that alone may not have been enough to prevent the power amp's health-o-meter from reading the amplified waveform as a fault and knocking things down just to be safe.

metro_area · #3 06-03-2010, 01:19 PM

Thanks for the help. Upon closer inspection, I do have the MXR pedal setup in a way that the power source could have gotten bumped when being stomped on and off (as in pedal engaged and disengaged/bypass mode). I could see that being a 'powered down' issue that sends too many volts to the input stage. You might have solved my problem!