roblpm Posted October 27, 2018 Share Posted October 27, 2018 Aaargh...... I bought a second hand GKMB800 off ebay and a new Barefaced Bb2 a few months ago in preparation for getting some gigs. Luckily I haven't yet..... I always practice on headphones at home so have really hardly used this setup in anger. The other three members of my family are out at the Queen pic (which I declined due to actually having been at Live Aid so I don't think I need to see myself in CGI....). Anyway spent an hour playing reasonably loud. But not mental. Gain and level on amp still a lot below noon. Just going to stop and something seems to have gone wrong! Now at noon the volume has about halved and there is a nasty fuzz. I thought maybe a flat battery on my behringer bddi thing but no. I sort of can't believe it..... Keep thinking it is me! Now obviously I know I need to test the amp with a good speaker and the speaker with a good amp but I can't do that for a few days. In the meantime I will obviously fret. Which is more likely to have half blown?! I have tried both channels on the amp. Same. I suppose i should go and buy another speakon tomorrow. I have tested the bass and cable through the mixer and headphones I usually practice on and they are fine. Grrrrrrr. What does a blown driver sound like?!!!! Can an amp half blow up?! Why me?! Seems like if I get a gig I need a spare amp. Although actually I do have some QSC K10s that actually could probably work in an emergency. Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 Ok i think there isn't much mystery. I hadn't thought to try the headphones out on the amp. Unplugged the bb2. The headphones out sounds the same. And there is a nasty click turning the amp on and off even with the mute on. So how do you get a gk amp fixed?????!!! Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 And its gonna get relegated to spare!!!!! So what am I gonna get instead....... Should I buy new?!!!!! Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted October 27, 2018 Share Posted October 27, 2018 Having got as far as narrowing down the fault to the amp, I'd check the preamp outputs and tuner outputs for distortion. This will tell you whether the fault is in the Amp or the preamp. The former is likely to be much more expensive, but the latter may be as simple as dirty contacts on the FX send and return sockets. David Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 3 minutes ago, Mottlefeeder said: Having got as far as narrowing down the fault to the amp, I'd check the preamp outputs and tuner outputs for distortion. This will tell you whether the fault is in the Amp or the preamp. The former is likely to be much more expensive, but the latter may be as simple as dirty contacts on the FX send and return sockets. David I think its the preamp....? Sounds bad on the headphone out? Is my logic correct?! Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted October 27, 2018 Share Posted October 27, 2018 56 minutes ago, roblpm said: I think its the preamp....? Sounds bad on the headphone out? Is my logic correct?! I may be wrong, but I think headphones are normally fed from the main amp via an attenuator, so: a) using your bass to BD121 to Fx-return would bypass most of the preamp, and b) using bass to BD121 to amp input, and Fx-send to mixer to headphones would bypass the amp Make sure to make all the connections with the power off and the volume controls off to avoid noisy surprises. Siully question, but can't see the answer in your original post - have you tried bass to GK to BF cab without the Behringer, in case it is the faulty item? David Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 22 minutes ago, Mottlefeeder said: I may be wrong, but I think headphones are normally fed from the main amp via an attenuator, so: a) using your bass to BD121 to Fx-return would bypass most of the preamp, and b) using bass to BD121 to amp input, and Fx-send to mixer to headphones would bypass the amp Make sure to make all the connections with the power off and the volume controls off to avoid noisy surprises. Siully question, but can't see the answer in your original post - have you tried bass to GK to BF cab without the Behringer, in case it is the faulty item? David Great stuff thanks. I will try tomorrow. Yes the first thing I did was remove the behringer. Then check all the knobs. I couldn't believe it wasn't just me being stupid but I don't think it is.....! Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 So i tried that stuff. The level on the power amp seems very low when fed from the effects return. Then the effects in to the mixer sounded fine. Then didn't..... Then I tried back with the speaker. There is a nasty click when turning on even with the mute selected on the amp. And this time sort of pulsing noise......! I think i give up. Needs looking at. I have messaged Polar. In the meantime I think i need a backup amp.......... Quote Link to comment Share on other sites More sharing options...
itu Posted October 27, 2018 Share Posted October 27, 2018 Did you try a guitar, sorry, a bass cable into the FX loop? (DC) Snaps tend to have something to do with grounding or connection issues. Last page has a block diagram: https://static1.squarespace.com/static/52d881e0e4b093afad1a2ae2/t/54a30e8ae4b0d05e1a9b7120/1419972234034/mb800-manual.pdf I would try every connection and a switch at a time to try to limit the problem to some block if possible. Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 27, 2018 Author Share Posted October 27, 2018 8 minutes ago, itu said: Did you try a guitar, sorry, a bass cable into the FX loop? (DC) Snaps tend to have something to do with grounding or connection issues. Last page has a block diagram: https://static1.squarespace.com/static/52d881e0e4b093afad1a2ae2/t/54a30e8ae4b0d05e1a9b7120/1419972234034/mb800-manual.pdf I would try every connection and a switch at a time to try to limit the problem to some block if possible. Great thanks. I better not try it all now...... Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted October 28, 2018 Share Posted October 28, 2018 Having seen the block diagram, I suggest starting with a mic cable from the DI out to your mixer. That will check out the whole preamp (post EQ) or just the input stage (pre-EQ) while bypassing the Fx sockets (which might be the problem). David Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 28, 2018 Author Share Posted October 28, 2018 22 minutes ago, Mottlefeeder said: Having seen the block diagram, I suggest starting with a mic cable from the DI out to your mixer. That will check out the whole preamp (post EQ) or just the input stage (pre-EQ) while bypassing the Fx sockets (which might be the problem). David OK. Good shout. That's fine. (and actually all instructive as to how the thing actually works!). I have seen other threads with complaints about the Fx sockets and last night when I used a jack cable between the out and in it did seem to fix the problem for a moment before it came back. So either them or the power amp? Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 28, 2018 Author Share Posted October 28, 2018 Hmmmm. So tried effect send out which is next stage. Fine..... But then thought I bet it is a contact problem or something. So guess what whole thing is fine. Has a nasty click turning on when muted though. Which wasn't there before. So something not right..... Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted October 28, 2018 Share Posted October 28, 2018 (edited) if you don't know its history, it's possible that whatever ambient crap the fan pulled through it has tarnished the Fx socket contacts, and also some of the other switches, so yes you probably need an amp tech, but it may be no worse than cleaning the various contacts in the signal path. This is the type of jack socket fitted to the FX circuit of a Hartke HA4000 This is the state that the contacts were in This is what they looked like after cleaning David Edited October 28, 2018 by Mottlefeeder Spelling mistakes Quote Link to comment Share on other sites More sharing options...
roblpm Posted October 28, 2018 Author Share Posted October 28, 2018 35 minutes ago, Mottlefeeder said: if you don't know its history, it's possible that whatever ambient crap the fan pulled through it has tarnished the Fx socket contacts, and also some of the other switches, so yes you probably need an amp tech, but it may be no worse than cleaning the various contacts in the signal path. This is the type of jack socket fitted to the FX circuit of a Hartke HA4000 This is the state that the contacts were in This is what they looked like after cleaning David Great thanks. I think it will be fine but needs going over..... Do you think that might explain the click on power up as well? Any ideas of best amp techs? Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted October 28, 2018 Share Posted October 28, 2018 2 hours ago, roblpm said: Great thanks. I think it will be fine but needs going over..... Do you think that might explain the click on power up as well? Any ideas of best amp techs? Dirty contacts may be the cause of your switch-on click, or alternatively, a faulty output relay could cause that, and the distortion that you are hearing. I've only used Ashdown to repair one of their amps (fried by a faulty generator), so I cannot comment on amp techs in general, but there have been threads on that topic. David Quote Link to comment Share on other sites More sharing options...
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