james.sealey Posted December 11, 2009 Share Posted December 11, 2009 Hi Guys Bit of a technical question for a Friday morning, but I need some advice/guidance on an audio coil to convert an unbalanced signal to a balanced one. I already have a nifty little unit which I acquired a while ago which is essentially two phono sockets in, two coils and then two balanced XLR outputs. It's unpowered and doesn't seem to attenuate, as when plugged into a balanced line level input on our desk I get a reasonable line level signal. However I want to replicate this unit, but I cannot see any markings on the coils inside to indicate what I need to get? I did stumble accross these, but I'm not 100% sure any of them are what I need? Taking a stab in the dark, I would reckon I need the NTE10/3 which has one singal primary winding, and two secondary, which I'm guessing would produce a balanced signal. Can anyone with any more knowledge/experience/know how point me in the right direction? TIA James EDIT TO ADD: I know there are ready made units that I could buy to fulfill this requirement, but quite frankly the prices seem a bit... ridiculous for what they are, and I'd rather get something built myself. Link to comment Share on other sites More sharing options...
mervaka Posted December 11, 2009 Share Posted December 11, 2009 when you say coils, do you mean a transformer? Link to comment Share on other sites More sharing options...
james.sealey Posted December 11, 2009 Author Share Posted December 11, 2009 when you say coils, do you mean a transformer? Yes, sorry. Should of said, I know different people in different areas of audio/elastictrickery refer to them differently :P Link to comment Share on other sites More sharing options...
mervaka Posted December 11, 2009 Share Posted December 11, 2009 no worries. in that case all you'd need is a transformer with a centre tap on one side. make sure the impedances on each side match your application. Link to comment Share on other sites More sharing options...
Brian Posted December 11, 2009 Share Posted December 11, 2009 Taking a stab in the dark, I would reckon I need the NTE10/3 which has one singal primary winding, and two secondary, which I'm guessing would produce a balanced signal.Nope, you only need a single secondary as you're not really making a 'balanced' signal. What you are making is a floating signal ie the signal has no reference to ground for its operation. One circuit would be this... ...the connection to the outer of the phono to ground being optional. Link to comment Share on other sites More sharing options...
revbobuk Posted December 11, 2009 Share Posted December 11, 2009 You don't want the NTE10/3 - that has a secondary outputs tapped to give either 3x or 10x gain, not a single centre-tapped winding. But you don't need a centre-tap: have a look at Shure's application note here for an example. And for that circuit the 1:1 Neutrik transformer would be fine. [note to self: learn to type faster!] Link to comment Share on other sites More sharing options...
james.sealey Posted December 11, 2009 Author Share Posted December 11, 2009 Thanks for the input guys. One question though, in relation to Brians suggestion, in the current unit I have the input and output grounds are isolated, I'll try and get a photo upp'd of the PCD layout which may help? Thanks again James Link to comment Share on other sites More sharing options...
Hilary Watts Posted December 11, 2009 Share Posted December 11, 2009 What about the ready built unit mentioned in this post ? I've just bought one and put it in a slightly larger box with jack sockets for connections but I haven't got round to trying it yet! Edit to correct link Link to comment Share on other sites More sharing options...
james.sealey Posted December 11, 2009 Author Share Posted December 11, 2009 What about the ready built unit mentioned in this post ? I've just bought one and put it in a slightly larger box with jack sockets for connections but I haven't got round to trying it yet! Thanks Hilary, I have seen those around, but they have an unbalanced phono output. I think I'm best opening the unit I acquired and getting some pics on here for you guys to get a clearer picture of what I have in my head! Thanks James Link to comment Share on other sites More sharing options...
Brian Posted December 11, 2009 Share Posted December 11, 2009 Thanks for the input guys. One question though, in relation to Brians suggestion, in the current unit I have the input and output grounds are isolated, I'll try and get a photo upp'd of the PCD layout which may help?Depends on what the unbalanced kit is and what sort of earthing it has (if any). A 'ground lift' switch might not go amiss. Link to comment Share on other sites More sharing options...
james.sealey Posted December 11, 2009 Author Share Posted December 11, 2009 have a look at Shure's application note here for an example. Sorry revboduk, didn't thank you for that very informative link, most useful! Link to comment Share on other sites More sharing options...
mervaka Posted December 11, 2009 Share Posted December 11, 2009 Taking a stab in the dark, I would reckon I need the NTE10/3 which has one singal primary winding, and two secondary, which I'm guessing would produce a balanced signal.Nope, you only need a single secondary as you're not really making a 'balanced' signal. What you are making is a floating signal ie the signal has no reference to ground for its operation. One circuit would be this... ...the connection to the outer of the phono to ground being optional.my bad, brian! you're absolutely right there. it's too early in the morning for me.. Link to comment Share on other sites More sharing options...
jamesperrett Posted December 11, 2009 Share Posted December 11, 2009 Thanks Hilary, I have seen those around, but they have an unbalanced phono output. Yes, they have a phono connector on the output but that doesn't mean that it isn't balanced. Cheers James. Link to comment Share on other sites More sharing options...
james.sealey Posted December 11, 2009 Author Share Posted December 11, 2009 Yes, they have a phono connector on the output but that doesn't mean that it isn't balanced. Unless I'm missing something (huge) here, a phono connector is NOT balanced. In my head, the definition (roughly) of a balanced signal is one where the '+' and the '-' of the signal not only travel down seperate cables to the 'screen' but also down cables which have the same impedance. By definition, a balanced cable/connector therefore must have 3 'pins': '+','-' and 'screen'. Examples being 3pin XLR, Stereo jack plug etc. Connectors such as phono or mono jack are UNbalanced. James Link to comment Share on other sites More sharing options...
bruce Posted December 11, 2009 Share Posted December 11, 2009 Not quite, it's perfectly possible to have 2-wire balanced circuits. Don't confuse the physical connector with the signal it is transmitting! It's only when you tie one end to ground that it becomes unbalanced... Take one of those cheapy boxes, connect the transformer outputs to pins 2/3 of the XLR, connect pin 1 of the XLR to the ground of the icoming (perhaps via a ground lift switch) and you've built precisely the circuit Brian describes in his diagram. Connectors such as phono or mono jack are UNbalanced. Connectors are connectors. Balancing is a property of the circuit, not the connectors that make it up. Link to comment Share on other sites More sharing options...
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