palantir Posted March 9, 2008 Share Posted March 9, 2008 GreetingsI have 3 PRO-SIGNAL-MP33682 boundary mics, which are pwered by a 1.5v battery, in an inline box, which I would like to run on phantom power (Mainly because I keep forgetting to switch them on :) ): My question is, can this be done &, if so, by a moderately good soldererer? I have photo's of both sides of the PC board, if that would help ( Appears to be a small transformer, resistors & caps. Any advice gratefully accepted Pete Link to comment Share on other sites More sharing options...
palbin Posted March 9, 2008 Share Posted March 9, 2008 Hello! I am a PA rookie, so you probably shouldn't pay any attention to my voice, but basic physics/electrical engineering says that if you put the 48 Volts PP over two resistances in serial with x and y Oms of impedance, respectively, then there will be 48*x/(x+y) Volts over the first resistnce and 48*y/(x+y) Volts over the second. So if you measure the impedance x of the mic, then you have to put a resistance y that solves the equation 48*x/(x+y) = 1.5 in serial with the mic (in some convenient space inside the mic that you hopefully can locate), to end up having the desired 1.5 Volts for the mic, which is to say that 48*x = 1.5*(x+y) so that y = 46.5*x/1.5 = 31*x. Good luck, palbin Link to comment Share on other sites More sharing options...
Simon Lewis Posted March 9, 2008 Share Posted March 9, 2008 Pete, There's a chance ot can be done - it ws quite a standard thing years ago to open up the Tandy boundary mics to either use a more standard battery or convert to phantom. However, you may well have to change some components to handle the higher voltage. A schematic of the preamp / bias arrangements would be useful... Simon Lewis Link to comment Share on other sites More sharing options...
Paul TC Posted March 9, 2008 Share Posted March 9, 2008 it ws quite a standard thing years ago to open up the Tandy boundary mics to either use a more standard battery or convert to phantom. Some info on the Tandy PZM here PZM mods Link to comment Share on other sites More sharing options...
palantir Posted March 9, 2008 Author Share Posted March 9, 2008 Thanks for the repliesPaul, I've downloaded the topics & will try to get some help with the circuit locally. Simon, I have the schematic for the input module of my desk: Is that what you meant?Otherwise there are the pictures of the mic's battery box board, along with the resistor values, but I can't find the page detailing how to go about posting pictures to the forum: I know simply posting them is frowned upon. Why is it so awkward to find FAQ's etc. on here? Pete Link to comment Share on other sites More sharing options...
MarkPAman Posted March 9, 2008 Share Posted March 9, 2008 .......... I can't find the page detailing how to go about posting pictures to the forum: I know simply posting them is frowned upon. FAQ here. Just don't post anything too big. Why is it so awkward to find FAQ's etc. on here? Pete It's just a matter of knowing where to look. Seems obvious enough to me. ;) Link to comment Share on other sites More sharing options...
Simon Lewis Posted March 9, 2008 Share Posted March 9, 2008 Simon, I have the schematic for the input module of my desk: Is that what you meant? No, we need the schematic for the mic's circuitry. We can safely assume that the desk input stage will behave much the same as any other! Link to comment Share on other sites More sharing options...
palantir Posted March 9, 2008 Author Share Posted March 9, 2008 It's just a matter of knowing where to look. Seems obvious enough to me. ;)It's obvious when you know ...... I assumed there'd be something in the Help section Pete Link to comment Share on other sites More sharing options...
peternewman Posted March 9, 2008 Share Posted March 9, 2008 I assumed there'd be something in the Help sectionThanks for alerting us to this, I'll see what we can do to get some Blue Room specific content in the Help system. Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted March 10, 2008 Share Posted March 10, 2008 Just a pointer. I read a while back that most mics that take the AA/AAA cell can use phantom as an option, IE take battery out turn mic on and connect to phantom supply no reason why it would cause any damage to the mic if it didnt work like that as phantom is feed along Gnd (pin1) and pin 3, Where as standerd mic signal is sent along pins 2 + 3. Joe Link to comment Share on other sites More sharing options...
gyro_gearloose Posted March 10, 2008 Share Posted March 10, 2008 Not quite true. Phantom power puts the same DC voltage on both pins 2 and 3, and uses pin 1 for ground. Link to comment Share on other sites More sharing options...
Rob_Beech Posted March 10, 2008 Share Posted March 10, 2008 Gyro, when you say not quite true, what you meant was not at all true. And you are quite right. Not only this but some mics will not like the full 48v up em so to speak. So you have to be careful here. Some will be fine (particularly those which state you can use a battery or phantom power) but the ones that don't surely don't say this for a reason. It would be poor advertising if you manufactured a mic that could handle phantom power or a battery, but didn't say. Rob Link to comment Share on other sites More sharing options...
palantir Posted March 10, 2008 Author Share Posted March 10, 2008 I wondered about that - the mini XLR from battery box to mic has 1.5v on pins 2&3:If I shove 48v down the line, this would go to the (secondary?) of the transformer, so would it fry; either the transformer or the desk circuit?Pete Link to comment Share on other sites More sharing options...
gyro_gearloose Posted March 10, 2008 Share Posted March 10, 2008 Well I thought that saying 'Not quite true' would be a bit more polite than 'You, sir, are talking out of your arse!' Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted March 10, 2008 Share Posted March 10, 2008 Other reason why I said this is because me Studio Master 16x2 desk is phantom on all channels non switchable (only all on all off) I always have it on because I use 2 condenser mics above the cymbals, and sometimes small ones for instruments when I have bands playing. But when you meter it, it only appears on Pins 1 + 3. All my other mics don’t have any problems cheap mics and SM58 work fine with phantom on. Joe Edit, did more research.... Sorry I stand corrected. I did a search on yahoo and came across a different forum, pin 1 is Gnd (-) pin 2 and 3 are both (+) .which is why I’ve never had any problems. Joe Link to comment Share on other sites More sharing options...
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