mutley Posted March 26, 2009 Share Posted March 26, 2009 Can anyone give a definate answer as to whether a Zero88 Betapack mk1 will work with a NEGATIVE control voltage?Our demux is set to -ve output for the four Strand dimmers currently installed, and we were looking at getting a couple more dimmers from usedlighting.co.ukTo keep it cheap, I was wondering if the Betapack mk1 dimmers they have for £200 would work with our -ve analogue output from the demux? Blue Room wiki says '+ or -', but usedlighting.co.uk say 'POSITIVE ONLY'... :D (The two £200 Act6 dimmers on their site have been sold!) Alternatively, if anyone has two Strand Act6 dimmers for sale (the same as those listed at £200), PM me! Link to comment Share on other sites More sharing options...
fedupbutstillworking Posted March 26, 2009 Share Posted March 26, 2009 Could I just point out that it only takes 10 minutes and a soldering iron to convert a lead, socket or plug. 0v isn't definitive: it's a point of comparison. It is worthwhile making sure things are labelled, though. Good luck. Link to comment Share on other sites More sharing options...
mutley Posted March 26, 2009 Author Share Posted March 26, 2009 Could I just point out that it only takes 10 minutes and a soldering iron to convert a lead, socket or plug. 0v isn't definitive: it's a point of comparison. It is worthwhile making sure things are labelled, though. Good luck. Actually, it is NOT possible to get around this by simply changing the wires round in the connector! Think about it, you have one 0v ground and multiple variable negative levels. Which wires would you swap?!! Theoretically, if it was a simple one channel device with a two wire control cable - Ground and data - you might be able two swap them round to get an inverted polarity, but in practice that wouldn't work either because of the equipment ground being connected to signal ground on the dimmer and the demux. The control voltage from the demux would short via the equiment earth. http://www.nwhoodz.pwp.blueyonder.co.uk/wrong%20wiring.jpg And since I haven't had any feedback on the control voltage inverter circuit I designed and built, which I lent to a Blue-Room member to evaluate back in December, :D the original question still stands.... Link to comment Share on other sites More sharing options...
Brian Posted March 26, 2009 Share Posted March 26, 2009 Well as you've probably seen in the manual it says '+ve or -ve auto-sensing'. However, something in the back of my mind says that is only the case when using them with a desk powered from the packs themselves and with the appropriate desk supply polarity selected internally. ie You can use a -ve output desk if it's connected to the pack and the internal link is set to give a -ve supply to the DIN connector. With a demux though I don't think it works like that. I can't find my Beta 1 circuit diagrams to double check. Link to comment Share on other sites More sharing options...
boatman Posted March 27, 2009 Share Posted March 27, 2009 Well as you've probably seen in the manual it says '+ve or -ve auto-sensing'. However, something in the back of my mind says that is only the case when using them with a desk powered from the packs themselves and with the appropriate desk supply polarity selected internally. ie You can use a -ve output desk if it's connected to the pack and the internal link is set to give a -ve supply to the DIN connector. With a demux though I don't think it works like that. I can't find my Beta 1 circuit diagrams to double check. It's a couple of years since I was inside one, but looking at the Betapack 1 service manual, it's definitely +10V only. There is a link to supply either +20V or -20V to the external desk. The diagrams I have originated in 1989, with mods in 1992 and come from the days when Zero88 was in my home town. Link to comment Share on other sites More sharing options...
PaulDF Posted March 27, 2009 Share Posted March 27, 2009 In can think of a way of doing this which uses a series of 1:1 operational amplifiers set up to invert the signal but will be a little bit of electronics and soldering work involved! Might be just as easy to buy another demux. Link to comment Share on other sites More sharing options...
Andrew C Posted March 27, 2009 Share Posted March 27, 2009 In can think of a way of doing this which uses a series of 1:1 operational amplifiers set up to invert the signal but will be a little bit of electronics and soldering work involved! Might be just as easy to buy another demux.Which DMux are you using? If you have the Zero88 variety, they have cards doing exactly this to give the -ve output. The positive is still available inside it; I wired several to have the +ve on the front, and added -ve on the back. Link to comment Share on other sites More sharing options...
ianknight Posted March 27, 2009 Share Posted March 27, 2009 Don't bother building circuits and buffers - the Mark 1 Betapack auto senses the control voltage polarity and acts accordingly - and yes, I just checked a very old manual to be sure (I could even check the service manual if you wanted) but the input stage runs through an inverterinternally that does the conversion. The confusion possibly arises because the desk supply voltage is switchable but this doesn't affect the control voltage. If you're using Beta's with a mix of racks i.e. Strand then it's good practice to set the desk supply to match the Strand because although the desk supply shouldnt be connected in the Demux (or anywhere else in such situations) they will short each other if positive and negatiove rails are bought together. If you're not sure that my advice is accurate then I'm sure either Peter, Keith or someone else from Zero will be along in a minute to agree with me.... Link to comment Share on other sites More sharing options...
PaulDF Posted March 27, 2009 Share Posted March 27, 2009 Just had a peep at the Betapack 1 service manual - it just and so happens to have a 1:1 inverting op amp on the input circuit (for when the supply is -ve) for each channel with diode bypasses (for when it is +ve input) so as ianknight says, it will automatically do what he says. Link to comment Share on other sites More sharing options...
paradoxism Posted March 27, 2009 Share Posted March 27, 2009 Unless I'm missing something, you don't have any spare demux outputs and so getting more analogue units would require another demux being added to convert your DMX in the first place? Or are you thinking of replacing the demux with a larger one as well? Link to comment Share on other sites More sharing options...
ianknight Posted March 28, 2009 Share Posted March 28, 2009 If it's a Demux 48 then he has plenty of outputs to go (enough for another 4 racks of 6) - it it's an old Strand Demux then he won't have enough but the intimation from the post (as I read it) is that outputs aren't the problem just his control voltage polarity. Link to comment Share on other sites More sharing options...
paradoxism Posted March 31, 2009 Share Posted March 31, 2009 Sorry ian - should have mentioned I have knowledge of the venue and it's currently a 24-channel demux, with another older 24-channel D54 demux which is now fairly obsolete as they use both an old Strand MX-24 and ShowMagic with DMX dongles that won't interface with the D54. Was off topic anyhow - apologies! Link to comment Share on other sites More sharing options...
ianknight Posted March 31, 2009 Share Posted March 31, 2009 Ahh - a cheap Botex ME72 from somewhere and either a couple of built spiders or a fully wired 25D cable and some soldering and Bob's your aunty then! Link to comment Share on other sites More sharing options...
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