B.Flat Posted February 12, 2017 Share Posted February 12, 2017 Hi all. I have an annoying wiring problem I am hoping someone can explain. OK, I have an amp I use for practice. Because of its limited tonal capabilities I run a YAMAHA FX500 in the send and return loop. The unit is powered by a 12volt power supply, centre negative. All OK so far. I have now added a ZOOM B1on ((battery powered but able to be powered by a 9volt supply, centre negative) between the amp send and the FX5500 input. Still OK. To tidy up the wiring I decided to put the two power supplies into the amp cabinet, running from the amp side of the on/off switch. The polarities have been respected. Result ? The FX 500 works fine, no prob. But the ZOOM unit powers up ok until it is connected to the send/return circuit, when it turns itself off. I have reversed the polarity of the power cable but no go. I have tried all variations of signal path, but still no go. I feel it must be an earthing problem but my limited intelligence is preventing progress! It works fine on batteries but I CANNOT get it to work on the 9volt power supply when connected to the amp or the FX500. There must be some boffin out there who can help explain this to me (I hope!!!!) Quote Link to comment Share on other sites More sharing options...
Subthumper Posted February 12, 2017 Share Posted February 12, 2017 (edited) Hi, strange problem you have there. I'd say something has changed regarding the zoom power supply and its output in relation to ground. See if you can get hold of another power supply and try that. Then ,if you can, see if you can see or measure any difference between them. Have you grounded the negative of the supply to the amp chassis? If so you should get +9v between chassis and psu centre pin. If you have grounded the positive by mistake it would explain why the fx unit works until you plug it into the amp as the output of the psu is floating and plugging in to the amp will short the supply to ground. I'm still thinking this out, will post again if I think of anything else. Good luck cheers Just Ps maybe some pics would be good. Edited February 12, 2017 by Subthumper Quote Link to comment Share on other sites More sharing options...
B.Flat Posted February 13, 2017 Author Share Posted February 13, 2017 Hi ST, thanks for your reply. I am a bit short of time to put the meter on but I will post what happens when I do. I have tried reversing the AC supply wirers in the psu but the same problem persists. I have mounted the DC female sockets to the chassis. These have three pins, I have used the centre tap and the sprung pin which contacts the body of the male plug. I have left the pins which are connected to the chassis (through the fixing) un-connected. Any comments on that? Thanks for taking the time to reply Quote Link to comment Share on other sites More sharing options...
Subthumper Posted February 13, 2017 Share Posted February 13, 2017 Have a measure and post up some pics. I'm pretty sure you have reversed connections to the dc output socket. Swapping the ac input won't make any difference, it's ac. Cheers Just Quote Link to comment Share on other sites More sharing options...
B.Flat Posted February 20, 2017 Author Share Posted February 20, 2017 hi again ST. The meter shows 9.4 v. I have reversed the polarity on the DC socket jus to be sure result being the ZOOM will not power up at all. What I cannot understand is that the YAMAHA unit, also neg. centre, works fine and is wired exactly the same way. If I take the YAMAHA out of the circuit the ZOOM will still not work. Do you think the psu could be faulty? Quote Link to comment Share on other sites More sharing options...
Subthumper Posted February 23, 2017 Share Posted February 23, 2017 (edited) Are you sure the psu is isolated from the amp chassis? Edited February 23, 2017 by Subthumper Quote Link to comment Share on other sites More sharing options...
pete.young Posted February 23, 2017 Share Posted February 23, 2017 Don't put the Zoom in the effects loop. It is not a line level voltage device. Put it in between the bass and the amp. Quote Link to comment Share on other sites More sharing options...
B.Flat Posted February 25, 2017 Author Share Posted February 25, 2017 I have put it between the bass and the amp with the same result. I now have it in the FX loop, powered by psu plugged into the same wall socket as the amp and this works fine in the FX loop. I am mystified !!! Quote Link to comment Share on other sites More sharing options...
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