previous: Rob Our band is breaking up in a month,... -- 7/20/2000 6:19 PM

Re: Need advice fast--SVT ground problems, maybe..

7/20/2000 8:00 PM

Reverb

Re: Need advice fast--SVT ground problems, maybe.. Rob,     SVT bass amps are built in a split-chassis configuration. There is one chassis for the preamp, and one for the power amp. These chassis are connected to each other with a single cable, which also carries the ground connection between them. If the cable ground is bad, the preamp chassis will not be grounded.     When I used to repair amps/keyboards/mixers for a living, I ran across an SVT that had a bad preamp to power amp chassis cable, which allowed a good 400V or so to build up on the preamp chassis ground. I measured it, so I know this is true. The preamp ground is connected to your guitar/bass strings through your instrument cable, and then to your body. If you touch something that is grounded while you are connected to 400V, you will feel a nasty shock.     SVT amps are something that ONLY experienced techs should work on, because they can easily kill someone who makes even a small mistake. To find out if your preamp chassis to power amp chassis ground is broken, you can safely do this:     1. Make sure to unplug the amp from the wall.     2. Set a multi-meter to measure ohms (200 ohm scale is fine).     3. Put one probe on the preamp chassis, and the other end on the power amp chassis. You should get good continuity.     Of course, other posts mention the ground polarity switches and possible reversed primary connections. If your guitar amp has one of these polarity switches, you could try flipping that also. I suggest using a voltmeter (instead of your band's bassist) to determine if an AC voltage exists between your instruments.     Chances are that your ground cable is not broken, but since I have seen that before, I thought it was worth mentioning. Have a very experienced tech do any repairs if you can't figure out what is wrong.     Best of Luck and Be Careful,     Reverb