Pre + Power amp problems

[mc_muench]

Alright so I recently started using a clean/dirty setup and for my dirty side I'm using a preamp + power amp rig.

I bought a Correct Sounds Eclipse, it's based off the preamp of a Sunn Concert. Its a great sounding preamp...when everything was working properly. The power amp is an old Acoustic 833 power amp.

Here's info about the Eclipse...
Link Removed

There's not much out there about the Acoustic 833. And all i know is its like 200 watts at 2 ohms.




When I first set it up, it worked fine for about 2 practices, about 10 hours total. But halfway through the 3rd practice with it, the entire rig dropped to a 1/3 of the volume and it sounded like it was clipping really bad and overpushing the speakers. My guitar player said something about pushing the voice coils too hard causing the speakers to stay extended.

First, I thought it was because I normally run the preamp with the gain and distortion dimed to create that great 70's SS distrotion. So I set it up to run clean, same thing, quiet and super clipped sounding. I unplugged the preamp and went straight into the Acoustic, it sounded fine.

Yesterday at band practice, I set up as a single rig not clean/dirty. And I blew a speaker, could the whole thing just be the end of the life of my speaker? Or is it my preamp? Is my preamp pushing my power amp and speakers too hard? What can rein er in, a comp/limiter? Or is it that old power amp?





Because I know TB loves pictures...

 

[B-string]

Have you checked the wall wort supply voltage for your preamp pedal? 18VAC is unusual, rectification and filtering would be done inside the pedal.

The old Acoustic power amp should be checked for DC offset at it's output. You would do this with no input to the amp, no cab hooked up, instead the speaker cable would be hooked up to a decent auto ranging meter (DVM,DVOM). Very little DC voltage should be present.

 

[mc_muench]

The power supply is correct, it is the one recommend by the guy that built the pedal.


What happens if there is DC offset at the Acoustic's output?



Any other opinions?

 

[B-string]

The power supply is correct, it is the one recommend by the guy that built the pedal.


What happens if there is DC offset at the Acoustic's output?



Any other opinions?

The pedal power supply should be tested for correct loaded voltage output in case it has gone bad.

If you see DC (above a few millivolts) on the power amps output it needs to be repaired before it can damage any more speakers.

 

[BassmanPaul]

My first thought was the same as Mr B's. The amp is outputting DC and needs to be repaired.

 

[jason weatherby]

Simple test if you don't have a meter: with no input to the amp, connect and then disconnect the speaker while watching the speaker cones; the cones should not move in or out and remain in the in or out position. If they move at all they should immed return to the neutral position with the amp still connected. If they remain in the in or out positions with the amp connected you have DC in the amp output. Not good.

 

[mc_muench]

Thanks guys! I'll test the power amp for DC output.

But why would this clipping thing only happen when I run my preamp or any pedal, I tried using my fuzz pedal as a preamp, in front of the power amp? When I run my bass straight into the power amp, it's works fine, no clipping or problems.

 

[B-string]

If you have high DC offset that uses up available headroom real fast from the power supply to output stage. Low gain input might sound okay, proper gain and the AC signal does not have enough swing left.

 

[mc_muench]

That makes sense! Thanks!