Members rovito Posted September 23, 2007 Members Share Posted September 23, 2007 Picked up an ABM 500 head in a used music store last Saturday. Used it Saturday night into one of my Mag410 cabs. Awsome results. Used it this past Friday into two of my Mag cabs with ok results. Sounded just ok but figured it was a different room and I just needed to tweak it some more. Seemed not as tight as before. Saturday night in the middle of the first set I played with the EQ alot and noticed I had the Gain and volume knob up almost to 3oclock each with not much sound. Then a flash of light and some smoke and it was all over. when I put my trusty Mag head back into the rig for the second set one of my cabinets was blown. Now i'm wondering if the speakers could not handle the lows from the amp and as the speakers died one by one the impedance dropped to an unsafe range for the amp causing it to blow, or did the amp take out the speakers when it died? I know the capacitors were changed right before I bought it and I have to wonder if there was a problem there. Any opinions? Link to comment Share on other sites More sharing options...
Members bikehorn Posted September 23, 2007 Members Share Posted September 23, 2007 I don't think the impedance would drop as speakers went out as the voice coil would still be in the circuit path. Even if it did that would only work if they were all wired in series. When a solid state amp fails, it can short to one of the power supply rails, which is DC and could be up to around 105-110 volts on some amps. Anyway, this means DC voltage appears on the output, where normally there is strictly AC(signal). Speakers don't like DC because it causes them to move in only one direction, and it quickly burns their voice coils out. To test this theory, if you have a multimeter you can (carefully!) measure DC voltage on the output of your amp. You should have less than 100 millivolts. Significantly more than that would mean the output has shorted to a PS rail. If this is the case, I'd be surprised that Ashdown didn't include a protection circuit. Link to comment Share on other sites More sharing options...
Members rovito Posted September 23, 2007 Author Members Share Posted September 23, 2007 Checked the speakers and got no speaker rub. I do not have my meter here so I will have to wait. When I run my home stereo through the cabinet it sounds ok but I will have to run it later at full volume to see if its a bad wire or something. As for the amp. I changed the fuse and fired it up. Got some sparks for a brief second and then it made a click and runs fine. Hooked it up to the cab in question and ran my CD player through it at low volume and it seems fine. If I blew an output transistor, would the others still work? Link to comment Share on other sites More sharing options...
Members bikehorn Posted September 23, 2007 Members Share Posted September 23, 2007 There are a few power amp designs that are able to run even when an output transistor is shot, but most will not. I've only seen that feature in PA power amps and it was an 'advertised' feature so I would doubt the Ashdown has it. If you're getting output that doesn't seem massively distorted, you probably didn't burn up an output device. I'm not an expert though....the click you heard was probably a relay, so maybe there is a protection circuit after all. Link to comment Share on other sites More sharing options...
Members rovito Posted September 23, 2007 Author Members Share Posted September 23, 2007 I may have a well done spider in there! Link to comment Share on other sites More sharing options...
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