Good Morning To All...........I'm just getting together a mobile disco which will run from a PC. Could some kind soul help me out on as to which cable i need to connect the pc to the Amp. I'm a complete novice to all this and at my old age its a steep learning curve and things take time to sink in

Regards Billy

Most PC's have a 3.5mm stereo jack output on the soundcard which is normally at line level or above. If it's a fairly modern sound card this will be coloured green.

The other end of the cable depends on what input sockets you have on your amp or mixer.

It is probably going to be 2 individual sockets rather than a stereo socket, and will most likely be either phono or 1/4" jack.

So you will probably need a 3.5mm stereo jack to 2 phono or 1/4" jack plugs.

Hope this helps.

Many Thx for your Reply I seem to recall 3 connections on the sound card of my computer....I've been reading the forums and gained some information<could you tell me is the quality of music after going through the amp dependant on which soundcard you have or will the sound be ok as long as soundcard produces a stereo signal.

btw....I'm not intending on being a professional outfit like most of you guys seem to be.
Regards Billy

I run a lappy as well as me cd drives, 3.5mm jack at lappy end and 2x phono plugs on other mixer end (most mixers) mine a beringer and its fine, but will say the music level output is lower for the lappy channel so i have to turn the gain right up on channel 3 (my lappy channel) so it matches the same volume as the cd drive channells....reason for this seems to be downloaded music can be a lot lower in volume than a cd (depending on the download) you have to be a little careful playing on a lappy coz each track can be at different volumes which seem nothing when played just through lappy speakers but when amplified through you mixer and amp make a lot of diffrence
Never happened to me but lappy running all night can get hot i use a sony vaio but older ones can be troublesome when over hot

I think I'm clear now on which type of lead i need.......Jeff just put the cat among the pidgeons when he mentioned connecting to the mixer... i was intending to use otsdj so i presumed no mixer would be required.and that i could connect from the pc to the amp then onto speakers. Would that arrangement be Ok

Regards Billy

Where would your mic go ?

Into the Pc..........Ipresumed

I doubt that would work - you can run it like you describe and use the software to mix but using an external mixer gives you far more flexibility (as well as a place to plug in your mic)

Cheers,

Jack.

External mixer all the way!!

Hi me again!! Mixer is the one matey! You cant cue next tune on a lappy anyway unless you have 2 sound cards built in...lappy to mixer to amp to speakers...beringer mixer good at about £130 (vmx1000) is great mixer for money and has seperate eq on all channels so you can adjust the sound as you like, also has seperate gains on each channel so you can adjust the lappy higher if required.... lots of other features too if you want them like auto talk over for the mic etc etc.......your lappy should have a half decent sound card already if its faily modern, i use winamp as the playing software (as me lappy is through my mixer anyway) so do all mixing through that and not on the lappy, having said that winamp has a built in mixer which you can set up to play next tune before previous finishes "so to mix" but your mixer is better to do that
hope thats helped
jeff

I was thinking on using a virutal mixer like otsdj...would this do the same as an external one ?

in a word no.... well not when doing a live gig. it may be ok in your bedroom but you need to be able to get hold of the fader when working at a disco with music and a mic...

Yep.. external mixer all the way.. and if possible have each virtual deck on a seperate mixer channel.. much better that way.

Our sound tech uses a di box to connect a laptop to the mixer at gigs don't really understand why? he says something about limit and balancing,

Just a note regarding connecting a PC soundcard to a PA rig. If you're using a laptop, there will usually be a little high voltage leakage from the PC ground connection to true earth. This is because of the RFI filters fitted to laptop power supply adapters. Make sure the laptop is plugged into your mixer BEFORE even plugging in the laptop adapter to the mains, or else there may be a nasty pop through your speakers (even with the fader down) and it may even crash the PC if you don't. Make sure there's a route from your mixer chassis to earth (either by earthing the mixer chassis if it's double insulated) or making sure your amplifier is not set to 'ground lift' if theres an option. If you dont, it could make your DJ mic, mixer deck or CD player remote float at up to 120V to earth, not dangerous but enough to give any user a small shock. This is often overlooked in Double Insulated equipment, (Class ii) but is becoming more of a problem as double insulated stuff is plugged into Class -1 earthed stuff. It's a similar problem when using domestic TV's and Karaoke players with PA systems. As a professional service engineer, I've seen many mixers with duff input channels due to this problem. If in doubt, power up your laptop, measure with a digital multimeter from the audio output socket ground ring to a real earth. You'll be surprised!!

Comments please.

K. Edwards

I'd comment - but I didn't understand any of that, I'm afraid LOL. Electricity is a mystery to me.

It worries be though, as I use a laptop. Any chance you could give us the "idiot's guide"?

Thanks,

Jack.

OK! Laptops are usually double insulated which means even when run off the mains charger-adapter, the chassis of the laptop, and any exposed metal (including audio output sockets) has a double layer of insulation between it and the mains connections. In theory, this is the safest form of appliance.

However, to comply with european regulations on interference (RFI and EMC compliance) the manufacturers have to insert components inside your adapter which connect from 240V live and neutral down to your laptop chassis. The consequence is that small leakage currents, harmless in general, flow from mains to your chassis and thus anything connected to your laptop chassis or outputs. If you have a double insulated mixing desk, (usually metal cased but with 2-core mains lead) then by virtue of your phono leads from PC to mixer input, the mixer will also 'float' at the same potential as your laptop chassis. If your amplifier has earthed (grounded) inputs, then great, your amp will sink these voltages to earth safely. But if you have the ground-lift switch on, or use floating inputs (eg Matrix Audio and others) then no leakage path exists...except through someone holding a microphone. Thats normally a small current, but if you have sweaty hands you might feel a tickle, or it may harm your mixer input circuit.

I think Ive just repeated myself here but I cant think of another way to describe the situation! If in doubt, set everything up but leave all mains plugs out of their sockets. Buzz with a continuity tester from any exposed metal on your laptop and go to the earth pin on your amplifier. If you dont get continuity, this could be a problem.

kevin

PS Modern appliances with lightweight switch-mode power supplies are the main culprits of this, eg VCR's, DVD players, laptops, TV's ......all due to the extra filtering required for the oscillator circuits.

Thanks - good explanation - I think I understand now.

I'm about to get my set-up PAT tested again and will ask the sparky to check this as well.

Cheers,

Jack.

Ok, good, but a PAT test will not show up any such a problem as it's not really a fault - only a design characteristic well within current EC specs. Just make your electrician aware of what I've mentioned.

Sometimes the leakage in portable TVs used in Karaoke setups can cause a similar problem, making the singers' microphones float at about 100v to earth if plugged into the karaoke player rather than the main mixer...!!

If its a pc , put 2 sound cards in. This way you can connect to 2 channels on your mixer. This way you can cue (or listen through your headphones) to the other player.

Ste

pat testing is a load of Im a sparky full time and its money for old rope!! Ive done loads of it and is a waste of time.... as who is to say the appliance went faulty the day after the test and you dont need another test for a year, all bull to be honest, but law requirement for some silly reason! a visual check on class2 equipment is the most important test in my view Class2 is double insulated and does not require an earth connection so its pretty hard to get a belt from it.
Class 1 equipment earthed/metal etc is another story and in my view is important to test, particulary the earth connection is present.
Most of our DJ gear is low voltage ie runs off plug in tranny's or class2!

Senario 1....lets say a dj had a pat test done and results were fine, but he trapped a lead in the van door the day after(exposing live wire), on his gig that night a kid got hold of the lead and was electricuted, whos to blame? The pat tester spark will deny all knowledge of seeing it which is the truth as it happened the day after, so the DJ is in for it!

OR senario 2
The damage was not noticed by the spark on the day of the testing or has seen it but couldnt be bothered to fix it, whos to blame now, as the spark will say...it wasnt there when i looked!
DJ in for it again
So whats the court gunna say? word against word?

The other thing is...lets say an earth test is done on a flashing light unit and was fine (earth connected from light to plug top)
But un beknown to the DJ, the socket he was plugging in to was not earthed (youd be supprised at the amount of un earthed property's there are) The light develops a fault during its flashing sequence and hey presto the lights metal casing becomes live (because no earth on socket) Kid touches it and gets shocked, who's to blame now? The pub/club....likely the DJ will get it in the neck again as they wont realise its because the socket was not earthed easier to blame the appliance!

Solution..............RCD socket outlets only true way of protecting yourself(recidual current device) Any probs to earth will trip it, keeping you and your bank balance safe. Trouble is they trip at only 30 milliamps of fault which isnt alot, so can trip easily and shut you down in mid come on eileen!! Hope thats informative lads?
Sorry off topic and ranting on a bit

Hi Jack yes and no.....RCD's come in diffrent trip sizes.... the lowest genrally is 30 milliamp up to 500 milliamp but the plug in ones you buy for a socket outlet are genrally 30 milliamp because the electrical regulations say that you must protect a socket outlet with 30 milliamps RCD and no higher. If it was higher i will not trip as quick (in a nutshell) As a contractor, i have to install 30 milliamp RCD for all down stairs sockets now by law.......because its likely that you will use a down stairs socket to plug an outside appliance in (ie) a lawn mower or radio for bbq or disco equipment!!
To be honest though, if a disco is inside, therefore the floor will be dry (hopefully) the full electric shock potential is far less than a wet/outside floor like grass etc

Sorry to bore you, RCD will trip if 30 milliamps of current flows to ground/earth....so if a person gets hold of a live wire, the electricity will flow through his body and down to the ground assuming the ground is a good path at the time, if the person is standing on a rubber mat, he will not create a path so wont get a shock anyway. RCD's trip when this voltage flows to earth therefore a must on an outside wet/soggy venue like i did last week (school summer fair) But inside its not as likely to trip as the floor should be a good insulator anyway in genral......Having said all that RCD's will trip on faulty equipment as well so good idea to use them anyway hope that all makes sense?
I never do....cant take the risk of my set up going down in the middle of a wedding etc just because of a RCD tripping...Just hide wires out of touch/reach!

Thanks for the response - I've never had one trip while playing but I might take your advice when playing inside.

Cheers,

Jack.

Look here if you want an RCD cheap !

RCD,s Bloody good but electricians nightmare sometimes