cfmjohn Posted September 13, 2007 Share Posted September 13, 2007 Hey there, I'm looking to build a Talkback box for a video production we're currently undertaking. Just wondering if anyone has any wiring diagrams/plans/personal experience I could draw upon. Tried this last month and had rather "varied" results so asking for help this time ;) What I really need is a full duplex comms system for up to 4 people (3 cams & vision mixer) for about £40 We had one before but it broke and was flung out before a replacement was made (grrrrr) The basic idea I had was to use cheap headset mic/headphones and wire them into a box with a mic preamp & power amp. But this didnt work out right and there was a constant Buzzing on the line. The mic inputs were all grouped together, fed into the preamp>power amp> back out to headphones down a long cable run (no beltpack needed). if anyone has any ideas id be soo greatful Thanks for looking at this weird request. cfmjohn Link to comment Share on other sites More sharing options...
Dmills Posted September 13, 2007 Share Posted September 13, 2007 The sidetone would be nasty, but something like this might work for you: In each users beltpack: Mic preamp (cheap opamp), say about 30 db or so gain.This feeds one core of the XLR via a 2K2 resistor and DC blocking cap.Another opamp wired to buffer the line for the headphones (variable gain for volume control), or small power amp (LM 386 possibly).The other core of the cable provides power and the screen is the return path.A 'Mute' switch is a good thing! Note that the beltpack is all single supply, so you will need appropriate bias and DC blocking caps. Also some headsets require DC bias for the mics, a few K from a couple of volts will normally do. At the head end, 12 V power across the screen and the power terminals, and a 220ohm resistor from audio line to ground to reduce the volume changes as more sets are added. That is a very simple version of the TechPro/ClearCom concept. Should be doable for a tenner a pack if you have a reasonable junk box and don't charge your time.... Regards, Dan. Link to comment Share on other sites More sharing options...
cfmjohn Posted September 13, 2007 Author Share Posted September 13, 2007 thanks mate, will give this a go tomorrow and let you know how I get on. cheers john Link to comment Share on other sites More sharing options...
Dmills Posted September 13, 2007 Share Posted September 13, 2007 Also, you should be able to hire the real deal for £40 from the normal sort of suspects. Regards, Dan. Link to comment Share on other sites More sharing options...
bruce Posted September 13, 2007 Share Posted September 13, 2007 Do a google, or search this forum, for "comclone". This has been discussed here several times before. Link to comment Share on other sites More sharing options...
paulears Posted September 13, 2007 Share Posted September 13, 2007 The budget seems a bit tight. 4 boxes, 12 sockets, 4 sets of cans, assorted plugs - that is easily over £40 without the electronics and psu? Maybe you already have these bits? Link to comment Share on other sites More sharing options...
cfmjohn Posted September 13, 2007 Author Share Posted September 13, 2007 The original idea was not to use 4 boxes at all. The way our old system worked was the headsets plugged into the multicore we use and were connected to a central distro box for comms. So there was only one box with a preamp, power amp & a global volume control. Basically all the headsets had their mics wired together & phones wired together. The mics went into the amp, and back down the headphone line using a common ground. (Ill draw a diagram & upload if it would be easier to understand) I have the headsets & cable already, its just the box that went and needs replacing. Although I am now thinking about a more flexible design with beltpacks etc if I can make a Simple one with just full duplex comms. No call lights etc etc. Link to comment Share on other sites More sharing options...
Tom Baldwin Posted September 14, 2007 Share Posted September 14, 2007 If I've understood your previous set-up correctly, then at some central point you have all 4 mic signals available, plus four headphone connections. Therefore, a mixer like this to combine the mic signals, plus a headphone amplifier like this ought to work, shouldn't it? Comes in around your £40 budget as well, when you add in shipping and the odd link cable. Link to comment Share on other sites More sharing options...
MarkPAman Posted September 14, 2007 Share Posted September 14, 2007 If I've understood your previous set-up correctly, then at some central point you have all 4 mic signals available, plus four headphone connections. Therefore, a mixer like this to combine the mic signals..... That's a line level mixer. Probably will not have enough gain for mics. EDIT: Try this one Link to comment Share on other sites More sharing options...
paulears Posted September 14, 2007 Share Posted September 14, 2007 I was going to bang on about all the potential problems, then suddenly realised that combining 4 mics, amplifying them and splitting them off to 4 headphones is actually quite elegant - as the master control would be able to turn off mics remotely if they picked up too much room sound, and even mute the headphones to some destinations if need be. I quite like the idea. Link to comment Share on other sites More sharing options...
boatman Posted September 14, 2007 Share Posted September 14, 2007 ..... EDIT: Try this one That looks like a good solution, but might need some balancing transformers when used around TV equipment. John Link to comment Share on other sites More sharing options...
Jivemaster Posted September 15, 2007 Share Posted September 15, 2007 Take the maplin MY95D mono mic mixer and use the maplin VE12N 3w audio amp kit to feed the headphones. get the stereo mixer MY96E and hack out one side's worth of bits and use the 4 spare jack sockets for the headphone sends, put the amp inside and get a small wall wart. Link to comment Share on other sites More sharing options...
bruce Posted September 15, 2007 Share Posted September 15, 2007 My guess is that although it will work, the long unbalanced mic-level connections will make it very noisy. Link to comment Share on other sites More sharing options...
Jivemaster Posted September 15, 2007 Share Posted September 15, 2007 Agree totally but sub £40 you are not going to get aerospace quality noise proof cans with noise cancelling mics. If the OP can run to a belt pack with battery and op-amp the mic signal could easily become line level and more easily sent over cables. Link to comment Share on other sites More sharing options...
cfmjohn Posted September 18, 2007 Author Share Posted September 18, 2007 well did the show last night. Didnt go too bad. Vision desk could direct the cameras (thats the important bit) But I'm going to look into a few suggestions here, because it would be a great deal easier & reliable. Cheers guys for the help Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.