chrisd24 Posted June 14, 2011 Share Posted June 14, 2011 I have an amp which needs a power supply (12v 2amp but with a negative ground) what do they mean by negative ground? is it referring to which way the polarity is set to the tip? Quote Link to comment Share on other sites More sharing options...
icastle Posted June 14, 2011 Share Posted June 14, 2011 [quote name='chrisd24' post='1268905' date='Jun 14 2011, 05:24 PM']I have an amp which needs a power supply (12v 2amp but with a negative ground) what do they mean by negative ground? is it referring to which way the polarity is set to the tip?[/quote] Yep that's right. What they're saying in a roundabout sort of way is that it's a positive tip. Quote Link to comment Share on other sites More sharing options...
chrisd24 Posted June 14, 2011 Author Share Posted June 14, 2011 [quote name='icastle' post='1268953' date='Jun 14 2011, 05:57 PM']Yep that's right. What they're saying in a roundabout sort of way is that it's a positive tip.[/quote] that gave me the confidence to plug in an adapter i had laying around and it works! although theres a distinct hum (kinda like a badly ground bass) with no instrument plugged in,and if i touch the chassis of the amp it silences it, is this a ground issue? Quote Link to comment Share on other sites More sharing options...
mart Posted June 14, 2011 Share Posted June 14, 2011 [quote name='chrisd24' post='1269002' date='Jun 14 2011, 06:31 PM']that gave me the confidence to plug in an adapter i had laying around and it works! although theres a distinct hum (kinda like a badly ground bass) with no instrument plugged in,and if i touch the chassis of the amp it silences it, is this a ground issue?[/quote] Sure sounds like it. What does your adaptor say it is? It should have a symbol like this: (in which case it's a negative-tip, which is the sort you don't want), or the same but with the + and - reversed (in which case it's the sort you want). Quote Link to comment Share on other sites More sharing options...
chrisd24 Posted June 14, 2011 Author Share Posted June 14, 2011 [quote name='mart' post='1269147' date='Jun 14 2011, 08:11 PM']Sure sounds like it. What does your adaptor say it is? It should have a symbol like this: (in which case it's a negative-tip, which is the sort you don't want), or the same but with the + and - reversed (in which case it's the sort you want).[/quote] Pos is going to the tip so the polarity's right,bit confused regarding an earth as this amp runs on battery's or 12v dc supply. Quote Link to comment Share on other sites More sharing options...
flyfisher Posted June 14, 2011 Share Posted June 14, 2011 Some 12 volt power supplies have 'floating' outputs. Thus, regardless of the polarity of the plug, neither output is connected to ground. As the amp will also run on batteries I guess it's designed not to actually require a ground connection. But, on the assumption that it could be run from a grounded PSU then they've specified that the ground should be connected to the negative side of the 12v supply - which is quite standard. If you have a multimeter, it would be easy to check if the PSU earth pin is connected to the positive or negative output, or neither (floating output). Also, some PSUs are 'smoother' than others and this can lead to hum issues - particularly with a floating PSU. In general, the cheaper the PSU the 'rougher' the output, but it requires some half-decent test equipment to really see what's going on with the DC output. If possible, it's probably worth trying a few different PSUs, though I realise not everyone has a box of them for such occasions. Quote Link to comment Share on other sites More sharing options...
chrisd24 Posted June 14, 2011 Author Share Posted June 14, 2011 [quote name='flyfisher' post='1269186' date='Jun 14 2011, 08:46 PM']Some 12 volt power supplies have 'floating' outputs. Thus, regardless of the polarity of the plug, neither output is connected to ground. As the amp will also run on batteries I guess it's designed not to actually require a ground connection. But, on the assumption that it could be run from a grounded PSU then they've specified that the ground should be connected to the negative side of the 12v supply - which is quite standard. If you have a multimeter, it would be easy to check if the PSU earth pin is connected to the positive or negative output, or neither (floating output). Also, some PSUs are 'smoother' than others and this can lead to hum issues - particularly with a floating PSU. In general, the cheaper the PSU the 'rougher' the output, but it requires some half-decent test equipment to really see what's going on with the DC output. If possible, it's probably worth trying a few different PSUs, though I realise not everyone has a box of them for such occasions.[/quote] Hi flyfisher, That all makes sense now,although this is a regulated supply so should be pretty smooth,also this has a metal earth pin on the plug so I'm guessing it would be plastic with no earth at all? Gonna borrow a multimeter tomorrow,think that is the only way to get to the bottom of this! Quote Link to comment Share on other sites More sharing options...
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