GK 400RB.. zapped and fried. Is it worth fixing?

Discussion in 'Amps and Cabs [BG]' started by Kelemvor, Mar 30, 2004.

  1. Kelemvor


    Mar 30, 2004
    North Georgia
    Its the first generation 400RB, 200 Watts. I used it at a show and someone had the powerstrip plugged into a ground lift. I got zapped by my amp and it hasn't worked right since. If the amp is plugged into a cab it makes horrible and very loud pops. Plugging a bass into the input jack does nothing, no sound at all. However, if I plug it into the effects return I can get a little sound out of the cab, but its muffled, soft, and filled with fuz and pops.

    I took off the top of it and I didn't see any obvious burned areas. Also the fuses are fine.

    I really don't want to throw it away... I'd like to get it fixed but I'm afraid it would cost more than the amp is worth. I have a SWR bass 750 now that I use during performance but I loved the tone out of that GK and I could find lots of uses out of it.

    Any suggestions?
  2. Well, I've seen those heads for about $1.00 per watt used and the newer ones for $250-$300. You could take it in and ask how much tofix it, but it usually costs something just to look at it. Is it worth it? Depends on how much you like it, and how much you have to spend on a new one.

    I'm going to go out on a limb and say that you fried your preamp sectoin. Were you pluggin in your bass when this zapping occured? Turning it on?
  3. Can you bypass the pre-amp and plug straight into the power amp section? Try that 1st to see if the pre-amp is fried.
  4. Kelemvor


    Mar 30, 2004
    North Georgia
    I think the damage occured when I turned the amp on. I got shocked when my finger touched the metal heat sink on the back while I was fiddling with my rack, trying to figure out why I wasn't getting any sound. :confused:

    All of this happened a year ago, the band I was in was playing with 3 other bands. The bass player before me had his ampeg rig hooked up to the same power strip and it worked fine, so I didn't have any concern about the source of power. I feel stupid now because I saw him plug the groundlift into the power strip, I just didn't know how dangerous that was at the time. I guess he was just as ignorant as I was. The microphones were shocking people that day too if I recall.

    Anyway, I learned an expensive lesson I guess. Now I have a sampson power conditioner with meters, and I have more respect for electricity :) .
  5. Kelemvor


    Mar 30, 2004
    North Georgia
    Hey Greybeard, yeah, I tried running my bass into the effects return the other day. It didn't sound very clean at all, but I was getting some sound out of my bass. There were still some loud pops, and I had to have the master way up to hear anything. The power light comes on, so I know there is nothing wrong with the power supply or with a fuse. The power amp must work too or I wouldn't hear the loud noises out my cab.
  6. Not necessaryily. I bought a junked 800RB a couple of years ago that made an awful noise - *loud* 60hz hum - and it turned out to be the power amp. The power transistors had literally blown up - made hole in the circuit board and blew little black particles all over the inside of the amp. The guy I bought it from thought it was a jack (lol). And sometimes the power light is in the circuit before the transformer and/or rectifier so it could be the low voltage supply for the preamp.

    But the fact that you get no sound at all throug the preamp makes me suspect it. You could have blown a cap in there - that might explain the noises. Likely you blew out an op amp too.

    p.s. if you decide to junk it I'd send a few bucks your way for it. I like fixing that sort of thing.
  7. Kelemvor


    Mar 30, 2004
    North Georgia
    Yeah, if I plug in a cable into the input jack, there isn't ANY sound, not even the usual 'pop' sound if I have the gain turned up. Maybe I'll take a picture of the inside and you guys could see something that I don't.

    I would love to get it working again so I can experiment with some bi-amped rigs and for use at home with my little hartke 2x10 for practice.
  8. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    That sounds like both the pre & pwr sections to me. I have one of those beasts. If I plug into the effects loop return I get full volume with a cheap pre and the MV up.

    I'd be dragging that one to the repair shop for an estimate. It's probably worth the 30 bucks to know. One this to be aware of, if that these amps get really flakey and act wierd is the ground is not solid ... If you fix it, have a new power cord attached at the same time.
  9. Kelemvor


    Mar 30, 2004
    North Georgia
    Well, one reason I'm here is that maybe someone with electrical experience will help me out and I won't have to pay 30 dollars :). I was sent here to look for some guy named Dan who works at GK. But anyone else can help me if they have a good idea of what happens to a 400RB if its turned on while ungrounded in a rather old building with bad wiring.

    But yeah, thanks for all the advice so far. I might just end up driving a couple hours away to the nearest GK authorized repair shop if I think I can get it fixed for under 100 dollars.
  10. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Not even Dan will be able to tell you what is wrong with that amp and how much it will cost to fix without performing an actual inspection of it. You need to either get it to an authorized GK repair center, or send it back to GK. There's nothing anyone can tell you here that will make any physical difference in that amp for you. Best of luck for a cheap repair.
  11. winston

    winston Supporting Member

    May 2, 2000
    Berkeley, CA
    Search on TB user name "Daniel Elliott" to contact the GK rep here.

    I had my '87 400RB fixed last year by the GK factory for $60 in less than a week. It had been acting up for years--turns out there was a blown IC in the boost circuit. Receptionist Lani and tech Arnel @ GK were both very helpful and courteous. The amp had previously been serviced by a local tech who wasn't able to correctly diagnose/fix it, so I'd recommend either the factory or a GK authorized service center for best results.

    Now it works like a charm--in the past 3 months I've used it 3-5 times a week for both BG and upright bass at countless rehearsals and gigs. Sometimes I go through the preamp and sometimes I use a SansAmp BDDI or Fishman Platinum EQ into the FX return.