Mottlefeeder

[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

Yes, each socket and plug is an extra joint that could become noisy, and will cost you to buy. You can use cheap grommets and cable ties to anchor the cables inside the box, or use a cable gland that includes a cable clamp. e.g. Maplins UP95D or JH23A or equivalent, to suit your cable diameter. Maplins switch FF75S is a 3 pole 4 way, which would do, as would their FF74R 2 pole 6 way. You can restrict the 6 way so that it cannot go past position 4. David

The screened cable is single core - instrument cable rather than microphone cable, and if you bring it into the box through a grommet, you can wire it directly to the switch. for other internal wirng I suggest 7/0.2 (seven strands of 0.2mm each), or you can use any wires stripped out of a mains cable - colour is not important ans size is not important. By the way, there is only one switch, but it contains both sections. When you build it, I suggest using a box that is not as high as your rack panel, and using screws and/or the switch mounting bush to mount the box on the back of the panel. That way, all the unscreened cables and ends of cables are contained in a metal box and will not pick up hum. If you do not have the gear to drill large holes in metal, you could use a plastic box and then line the inside with copper foil - you can get it in sheet from from guitar-spares shops on-line, or you can use slug-repelling copper tape from your local garden centre - garden centres are expensive, but so is postage on a small mail order. David

Here we go... David

I've drawn the basic switching circuit, and how you connect the cable cores and earthed screens. If others chip in with click suppression, I can add that (assuming I understand what they suggest... First problem - my scanner at work produces PDFs, which Photobucket ignores. I'll photograph the page when I get home. David

I'll try and draw something, scan it and file it on photobucket and post the link here. Hopefully by tomorrow evening. David

Assuming that you change the instrument connected you your wireless transmitter, and you want to switch the receiver to feed the correct preamp for that instrument, I think you only need one switch - a rotary switch with three positions (four if you want a 'mute' position), and two poles, one for the preamp inputs and one for the preamp outputs. I would also aviod the use of a patch panel - it will cost you for the plugs and sockets, and give you more places where you could get a faulty contact. A metal box containing the switch, connected to 8 cables which end in jack plugs, would be cheaper and more robust. David

Pinball - you have a PM David

I agree with Bassbod - a passive bass into a passive DI is likely to lose all your top end. Unless you like that sound, I would regard that option as a get-you-home-spare only. Something like a Behringer BD121 second hand would be a cheap and effective active back-up. David

I ran a church PA system with a loop for several years, and some of the comments here are not quite right. An induction loop is like a loudspeaker coil, and carries audio frequencies - it is not a spot frequency transmitter like a radio, so it is unlikely that you can notch it out. An induction loop is designed to carry a specific signal level, and the amp has built-in limiters so that it will not cause problems by overloading any hearing aid transducer within range. An induction loop is often run under the floor, a few feet in from the wall. This gives better coverage, but also gives a dead spot directly over the cable. You may find a location where you do not have a problem.. Passive instruments can pick up even with their volume turned down, because of the way they are wired. Active instruments will not pick up when their volume is at minimum (not much use when you are playing, but might be of use when you stop) Jazz basses have a hum-bucking facility built in to them because the pick-ups have opposite polarity, so they cancel pick-up when when you set the pick-up volumes to be equal - the slightly nasal sound you are left with is the difference in string resonance at the pick-up positions. The induction loop has to be getting a signal from the band in order to feed it back to them, so if you are using your own PA, look for a live microphone on their system - if you are using their PA, turn down the auxilliary sends. Hope this helps David

Now gone. Mods - please retitle and move (or tell me how to do it) Thanks David