napierzaza Posted February 13, 2007 Report Share Posted February 13, 2007 I just found some old PSUs that provide the following: 5v 1.0A+12v .2 A-12v .2AIs that enough current for a Midibox FM? How much 12V and -12v current does it need to function? Would I be able to power 2 FMs off this?Also, can the different between 12 and -12 vdc be explained briefly? I'm kind of puzzled as to how that might work, or how I could think to supple -12v. Quote Link to comment Share on other sites More sharing options...
moxi Posted February 14, 2007 Report Share Posted February 14, 2007 yes it's enough for power the FM module with the +12/-12V, but for the core you need at least 7.5v, 9 is well. 5v is the voltage you find on the core after the regulator. Quote Link to comment Share on other sites More sharing options...
Lall Posted February 14, 2007 Report Share Posted February 14, 2007 Is the old PSU providing regulated 5v DC?If so, that should be suitable for supplying a Core but then you should not mount the regulator stuff on the Core.Note you should leave some big enough capacitors on the Core though so that it's correctly decoupled.Last but not least and forgive me if obvious, you should check that the Core + the LEDs + your LCD and especially its backlight do not require more than 1.0A otherwise you'll run into trouble. I'm pointing out your attention on that as I've been myself veeery surprised about the consumption of my LCD backlight.Best regards,Lall Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 14, 2007 Author Report Share Posted February 14, 2007 Really? It can consume more than 1A. It seemed to me that the 5 wouldn't be a problem! So is it enough for 2 cores and 2 FMs? Quote Link to comment Share on other sites More sharing options...
seppoman Posted February 14, 2007 Report Share Posted February 14, 2007 Hi,the question still is - are the voltages all regulated DC?About consumption: the +-12 V are not a problem. This is only needed for the FM module´s OpAmps. Probably even 50mA would be enough.5V DC 1A are definitely enough for one MBFM. I don´t see why you would need 2 of them. But if you really want them, you probably want one with full CS and the second one only as a Midi slave? For that, 1 A will be enough. The things that consume most power are generally LCD backlights and LEDs, so for two FMs with only one display/surface, 1 A will be sufficient.Seppoman Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 14, 2007 Author Report Share Posted February 14, 2007 Well in terms of regulation I don't know, haven't opened it yet. But considering no one's really explained the -12v concept I see no other alternative source for such a voltage (it's not just a ground for the +12 is it?). Is it actually possible to make a midislave that is slaved to another FM? If there are any articles please let me know. I was going to have 2 in the same case with the same PSU. Quote Link to comment Share on other sites More sharing options...
Lall Posted February 14, 2007 Report Share Posted February 14, 2007 Concerning the load, I was wondering how many LEDs out of the 34 can be active at the same time at maximum. I have never really got enough time/motivation/patience to dig into the manual and CS to check that (I don't have built my FM yet). Does anyone know about that max number? That can quite influence the max load actually.Because, let's imagine the worst-case with 34 LEDs active each consuming 10mA. Imagine you have a LCD with a backlight consuming 280mA (like mine) and a Core that was said to consume ~100-120mA. You already come close by the 750mA so OK it's not yet 1.0A but that's big too from a certain perspective. I would say it's always wise to take a look at the datasheet of the LCD, look at the resistor chosen for the LED, look at the Cores, ... and compute the sum... Otherwise then use an over-dimensioned lab power supply to measure the actual current consumption and "design" the embedded PSU based on that :)For the -12V, that's really a 12V with an opposite sign to the usual 12V compared to the GND. So if you look at the difference between the -12V line and the 12V line you'll get 24V in total... I'm not sure the diagram below will make it more clear:+12V ---------- --------- 12V diffGND ---------- 24V diff 12V diff-12V --------- ----------Best regards,Lall Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 14, 2007 Author Report Share Posted February 14, 2007 Okay, I do understand what you mean, but let's say I just bought 3 -12 Voltage REgulators from mouser. What Voltage should I be putting throught this to make it give off the least heat? I guess 1 V or something unless I can find a different negative voltage PSU right? Quote Link to comment Share on other sites More sharing options...
Lall Posted February 15, 2007 Report Share Posted February 15, 2007 Hi,The thing is that if the old PSU you plan to use is already providing regulated DC output then you will not need the +12V and -12V regulators on the FM side but just capacitors for correct decoupling.If that is AC output, then you'll need a bridge rectifier and a regulator. The bridge rectifier as the ones used in MBHP should have a drop of 1V to 1.5V and the regulator has a typical drop of 2V.Best regards,Lall Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 15, 2007 Author Report Share Posted February 15, 2007 Sorry, what I meant was, if I wanted to make my own PSU, are there -12v transformers (or I guess -14->-15v)? Quote Link to comment Share on other sites More sharing options...
seppoman Posted February 15, 2007 Report Share Posted February 15, 2007 Is it actually possible to make a midislave that is slaved to another FM?No, it´s not possible in the way the MBSID does it. But you could build one full FM and another one without control surface. So you´d have the full one for editing patches etc, and could just copy over the patches via Midi (and some Sysex manager/JSynthLib etc.).Main goal of 2 boxes is probably to have more voices/multitiblrality, and for that you won´t need two control surfaces.Actually I don´t see for what one would need more than 6 voices of FM - when you use it in big arrangement songs, there are (or should be for my taste) normally other synths (soft/hard) involved and the FM is just there to give some flavour. And when doing chip tunes, 6 voices plus 5 drum voices is plenty - after all, the whole chip tune concept lives from simplicity and arpeggios.if I wanted to make my own PSU, are there -12v transformers No, there are not :o There are 24 V transformers with center tap. As Lall explained before, "Ground" is just some reference point. From the center tap, the ends of the transformer are both 12 V away, one positive and one negative.But why don´t you give your existing PSU a try? I´d say it is probably regulated anyway. You normally can´t buy transformers with 5V AC output, so (95% chance) it´ll be regulated.And a question like the one above implies that your experience with mains voltage is very limited, so i´d strongly advise against tampering with lethal voltages!!!Seppoman Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 15, 2007 Author Report Share Posted February 15, 2007 Whoa! Fix that Quote Link to comment Share on other sites More sharing options...
Lall Posted February 16, 2007 Report Share Posted February 16, 2007 Hi all,I think I now get the 3 PSU thing you were referring to initially. If I now get it right, you have a +5V one, and two 12V ones, right?As Seppoman said, for the 5V it's 95% certain it's DC. For the 12V, take a careful look at them as there are some (what a friend of mine calls) "modem PSU" out there providing AC output but there are also DC ones. Normally, it should be written on the PSU in a way or another otherwise simply take a voltmeter and measure the output.Measuring is good anyway as it will allow you to double-check the polarity of the DC output. It's VERY important as if you don't mount the regulator, there's absolutely NO protection against inverse polarity and the chance that you'll kill most of the ICs on the board is pretty big not to say certain. (Note that I have no idea what the result is when you apply an inversed voltage to a regulator but I guess you may have trouble...).Best regards,Lall Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 17, 2007 Author Report Share Posted February 17, 2007 No, I have 3 PSUs that have 5v,+12v,-12v. I will certainly check with the voltmeter to make sure there's nothing going on. Thanks for the help with the PSU, I looks like it might very well work.I got me YMF cards today, mostly really worried about heating them too much when desoldering! Quote Link to comment Share on other sites More sharing options...
napierzaza Posted February 17, 2007 Author Report Share Posted February 17, 2007 Okay, what if the power supply is switching? This is bad right? What can I do to make it a non-switching power supply (what to look for inside)? Quote Link to comment Share on other sites More sharing options...
seppoman Posted February 17, 2007 Report Share Posted February 17, 2007 Okay, what if the power supply is switching? This is bad right? What can I do to make it a non-switching power supply (what to look for inside)?What if the power supply is no power supply at all? ;) If it is switching, you can´t do anything about it. But it also doesn´t mean it is necessarily bad or causing problems.Honestly, why don´t you just try it out before asking another dozen questions regarding problems you don´t have (yet)?I don´t want to sound rude but I get the impression from you that you use too many time for worrying and your life would get easier if you´d just spend part of that time building things :)Seppoman Quote Link to comment Share on other sites More sharing options...
TheAncientOne Posted February 19, 2007 Report Share Posted February 19, 2007 Purely from personal experience, but if you are making a small scale audio device, switching power supplies are often more trouble than they are worth. 1) The output a lot of electrical background noise, which can be hard to keep out of the audio.2) They often need a minimum load to work properly.3) Cheap ones can suffer catastrophic failures and take out the equipment they are connected to.4) Some of the cheap ones produce voltage 'spikes' on start up, which can damage your audio gear or ears.5) They are an 'experts only' job to work on or repair: they can kill you, and/or your test equipment.For anything MIDIbox, so far, I think linears are best, unless you have a gazillion LED's in your control surface . . . Mike Quote Link to comment Share on other sites More sharing options...
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