Walker Posted November 17, 2012 Author Share Posted November 17, 2012 Good evening. OK, I've decided to do Mk1 of this box with sockets, so I can move it around a bit, then one it's a permanent install, I'll run cable as David suggested. The project box is drilled, everything is ready to go together (see pic). I have a 2 pole 6 way switch. I'm not doing the tuner bit of David's diagram, so I'll just kill the master volume before switching or changing instruments. [b]Couple of questions:[/b] 1. I've redrawn the diagram so I can get it right in my head - is the diagram correct? 2. Can I join up all the earth wires as I have shown in my diagram or do I need a seperate wire from each point to the earth screw in my project box? I'm thoroughly enjoying this and learning loads, so thanks again, especially tov David and Bremen. I've got all the parts ready in case I have thumps or ground hum, apart from a couple of 0.1 microfarad caps as Maplin didn't have any in stock. Cheers Chris Quote Link to comment Share on other sites More sharing options...
bremen Posted November 19, 2012 Share Posted November 19, 2012 It's 1uF caps you need - 0.1uF will probably lose some low end if the input impedanceof the power amp isn't high. PM me for some free samples. Quote Link to comment Share on other sites More sharing options...
bremen Posted November 19, 2012 Share Posted November 19, 2012 If switch part A is the wiper for pins 7, 8, 9 and B is 1, 2 and 3, yes that's fine. Regarding earthing: you should be able to common the grounds as shown. Star grounding is only important if there are large currents flowing, as in a power amp, or high frequencies. If you do get hum, find where it's coming from by a process of elimination and lift the ground from the mains plug (this is safe so long as the units remain bolted into a rack, thus grounding all the panels) or do the RC thing. Quote Link to comment Share on other sites More sharing options...
Walker Posted November 19, 2012 Author Share Posted November 19, 2012 Bloody hell, it works! Quote Link to comment Share on other sites More sharing options...
bremen Posted November 19, 2012 Share Posted November 19, 2012 Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted November 19, 2012 Share Posted November 19, 2012 [quote name='bremen' timestamp='1353344199' post='1873971'] ... Regarding earthing: ... ... lift the ground from the mains plug (this is safe so long as the units remain bolted into a rack, thus grounding all the panels) or do the RC thing. [/quote] Lifting the earth in a mains plug is totally wrong, and dangerous. Firstly, you have no guarantee that your alternative earth will always be there, and secondly, leaving a loose wire in a plug is a very bad idea. Thirdly, if you play for money, using dangerously modified equipment, you will be breaking the law. The reason for having an earth connection on a mains powered equipment is to ensure that if there is a fault, and the equipment casing becomes live, enough fault current will flow to blow the fuse quickly, thus disconnecting the equipment and making it safe. Never mess with fuses or with mains (safety) earth connections. You can disconnect signal earths, or add in a small impedance as I showed in my diagram. This is the safe way to do it. Some years ago, the Health and Safety Executive analysed their database of reported electrical incidents, and discovered that there was no difference in the scenarios described in the fatalities, and in the incidents that just caused injuries. If you set up the conditions for an electrical incident, whether you walk away or die is a function of which bit of your heart beat is occuring when the shock current start passing through you. For every thirty incidents, one was a fatal - think of it as russian roulette with one live round in every thirty. David Quote Link to comment Share on other sites More sharing options...
Walker Posted November 21, 2012 Author Share Posted November 21, 2012 I installed this properly in my rack this evening and no hums or thumps - in fact, it has seriously reduced the humming I used to get from my Ampeg SVP Pro. That's a very welcome side effect... by why?!! Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted November 21, 2012 Share Posted November 21, 2012 I'll take a guess that the Ampeg input earth, or one of the preamp earths, was not too good, possibly due to tarnish, or cheap cable/plugs or whatever. Connecting everything together has improved the poor earth, resulting in less hum. As I said, just a guess. David Quote Link to comment Share on other sites More sharing options...
Walker Posted November 22, 2012 Author Share Posted November 22, 2012 Nice and neat from the front. I've got some tidier fasteners to go on... A bit more Heath Robinson at the back... Quote Link to comment Share on other sites More sharing options...
Walker Posted January 6, 2013 Author Share Posted January 6, 2013 [quote name='Mottlefeeder' timestamp='1352323131' post='1861779'] Here we go... David [/quote] In the little hum reduction doodah [A] in this diagram, does it matter which way round the capacitor goes? Thanks Chris Quote Link to comment Share on other sites More sharing options...
bremen Posted January 6, 2013 Share Posted January 6, 2013 No, non-electrolytic capacitors can go either way (ooer missus, fnarr fnarr etc) Quote Link to comment Share on other sites More sharing options...
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