Hi there!
Now planning the FM building… ;D
Looking at the pictures of TK´s great MBFM and saw the PSU…
Question 1:Where do I put the fuses didn´t see those on the “mbhp opl3 psu.pdf” are those necessery??
Question 2: I also want the 5V psu on the same board(like TK) and I found one 220VAC-6V 633mA are that enough?
Found 2x12V 159mA In not planning the AOUT.
Thanks
Christoffer
Anyone?? :-[
Christoffer
Question 1:Where do I put the fuses didn´t see those on the “mbhp opl3 psu.pdf” are those necessery??
Yes. At the very least fuse one wire of the mains supply with no more than 2A fast blow. (don’t use a slow blow here, your transformer will cook before the fuse pops)
The fuse on the mains is the one that keeps it from burning your house down if you accidentally leave it on and go on vacation. 
You can fuse the 12vdc side of the power supply also, Since the regulators are 1A I would use a 2A fast blow so that it only pops the fuse if there is a massive failure. One on each of the 12v lines, never on the common.
The idea is to pick a fuse value that pops quick enough to save some of the parts on the board. Too high and everything cooks before it blows, too low and it will pop when nothing is really wrong. (and naturally this happens during performance!)
Fuses are not just rated by current capacity, but also by time. The standard used depends on manufacturer and type, but a common glass slow blow fuse will open at its rated amperage after 15 minutes, and a fast blow will pop at it’s rated current after 1 minute. Again there is no official spec for this, so ratings are subjective and different from one manufacturer to another.
Question 2: I also want the 5V psu on the same board(like TK) and I found one 220VAC-6V 633mA are that enough?
Found 2x12V 159mA In not planning the AOUT.
Thanks
Christoffer
For the xformer on the 5v rail, I would go 9v if you can, While 6v works, its just is not much differential for the regulators to work with. 9v gives some breathing room and things run cooler.
Personally I would not use a weaker transformer on the 12v rails. Every component in the power supply (and depending on load every other component on your box) will have to work much harder if the transformer is less than spec, and future issues will be very hard to troubleshoot if your power supply is straining…Even if the underrated one works fine a larger transformer will cause everything to generate less heat…
Remember it’s always ok to substitute a transformer with higher current output for a smaller one as long as the voltages are the same, and the end result is a more stable power supply. I pick mine for 1.5x to 2x the actual load needed, then fuse correctly. ; )
Best!
Smash
i’ve found some wall warts with +5 and +12, -12v… will these be suitable for the fm? (i don’t know if they’re regulated or not)… would i need to take the 5c regulator off the core like if using a c64 psu on the sid?
all the best
adam
Duggle sent me this schematic for an alternative PSU:
Find attached a schematic for a split rail supply. This configuration is
well known (voltage doubler) and Ive used it many times before. Of course
before the design is posted, it should be verified by a constructor.
So, who wants to try this out?
Best Regards, Thorsten.
regarding this circuit…
i want to make this for the mbfm, has anyone tried it ?
it says to use 12V AC with 250mA but…
on the core it says 10V max with 500mA !!! should i change something ??
are D1+D2 are “1n4004”
is this the best sulotion for powering the mbfm ??
it says to use 12V AC with 250mA but…
on the core it says 10V max with 500mA !!! should i change something ??
Hey, It also says “see note (3)” - you’ll need to use an AC supply with a 1Amp current rating if you’re also going to power core from this solution.
are D1+D2 are “1n4004”
Yup, or anything in between 1N4001-1N4007 series.
is this the best sulotion for powering the mbfm ??
Well - I don’t want to lie to you, it’s probably not. But let me stress this: it’s a SAFE solution. There are no lethal voltages inside the box while using this method. For a safe alternative - you can always check if you can find a bipolar powersupply in an isolated box.. something with +/-12VDC, 1Amp output. I think that at least in the US these are quite a common and you can find them pretty cheaply on ebay.
I hope my answers satisfies you - you can always ask for another opinion.
Bye, Moebius
do u mean one of those :
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3309&item=5761461927&rd=1
(problem is here in Israel we use 220V not 110V !)
so what is the best sulotion to diy, in case i dont find something made ?
Hi rasOfir,
I offered this solution as it is extremely safe, easy to build and very cheap.
I shop at electronics disposal stores when I can, and there is one in my city
that has various plug packs for as low as $1.
It really reduces the work, the expense and weight and size demands of mounting and wiring
and switching mains transformers in your box, when you only need a few mA’s at different voltages.
The only drawback is that the core regulator will run a little warmer (due to the higher input voltage) and
will require small heatsink.
cheers
i’ve bought a ±12 and +5 wallwart from a surplus place… i’m planning to use this with a zener on the +5 line so as not to kill the pic… is there any cleverness i can do to make sure the supply stays above +5…? some kind of capacitor soaking up the excess power then letting it out when the voltage drops… i remember someone saying that the regulators need at least 6v to work best
Electronics Disposal stores? Surplus stores? Crikey where are you guys?.. I’m about to have to pay $30 for a 9VDC AC Adapter 
I wish we had stuff like that in Australia!
@stryd_one:http://www.rockby.com.au/index.htm checkout “clearance” pdf.
to my mind having to have multiple plug packs connected to your box is messy and to be avoided. Anyhow, is the 5V supply regulated? if so, it is a little difficult to come up with a protection scheme that is robust and guarantees to protect the core, given that the bridge and regulator will need to be bypassed. The danger is if the wrong kind of wall wart is plugged into your box. A parallel zener diode will offer some protection, but if say the wrong polarity, or AC instead of DC, or wrong voltage is plugged into your box, the zener will clamp, protecting your pic, probably go short,(depending on the wattage of the zener and time), this short will fry your wall wart. If you employ a series resistor to limit the clamping current then there will be a voltage drop which may cause the core and associated circuitry problems under normal operating circumstances.
The most failsafe power input stage protection is already in the core design, namely bridge and voltage regulator, and supplying at least 7.5V. If the bridge is replaced with a link and diode like in the circuit posted then the required input voltage is a little lower.Â
If the plug pack is not regulated, then it is normal for the voltage to be somewhat higher and it may drive the regulator output to 5V (or close enough).
hope this is clear, if not please ask.
cheers   Â
Badass! Thanks Duggle 
what i have is one plug pack which supplies +&-12v at 250ma and +5v at 1a (it has a din connector, so there is less chance of plugging the wrong supply in, i think i would mount it on another side of the case to separate it from the midi connectors, or put some kind of fighter jet style cover on top) i don’t think it is regulated, (it didn’t say so on the website anyway, and it doesn’t say so on the transformer) it doesn’t say that it’s unregulated either of course.. is there a way for me to check? (i have some din connectors, i could wire it up to some stripboard and watch the output with a multimeter i guess)… excuse my basic questions.. from what your saying it seems that i can wire the unregulated 5v up to a regulator as normal, but from what smash says it may run rather hot with only 5v so i presume i’ll need to heatsink it
one tip i learned from a guy with lots of computers is to put different coloured stickers on each machine and on each plug/psu.. makes it easier to unplug the right thing… i guess with a sticker or paint on the actual psu connector this would also help people plug the right psu into their device
I used to do that. You can buy rolls of little coloured ‘dot’ stickers in many different colours, theyre not too pricey, and certainly better than blowing things up They’re also just big enough to write numbers on them which can also be handy.
This idea has recently been adopted by Intel who’s motherboards started to have colour coded plugs for keyboards and mice and video etc. Actually it’s not so recent now I guess… I think I’m showing my age here hehehehe. DEC were first to do it I think, or perhaps it was compaq? Anyway they’re both hp now!
My studio takes about 6 hours to unplug all cables and 12 to plug them all in… It’s easy to get confused with that many wires… Problem is, wrapping labels around the wires leaves you with yucky sticky goo all over them as they age… Personally I think that the best thing is to use a paint marker (for those in AU, Artline XF series “outdoor” markers are the ones). You don’t get sticky residue, and you don’t have to follow a colourcoded plugpack’s wires all the way up the cable (which is often in knots) to the colourcoded plug on the device.
Hope this helps
NOW I M MORE CONFUSED !!!
would some one tell me the bottom-line ??
(if i cant find a ready-made ±12v 5v psu)…
WHAT SHOULD I DO ??
build this circuit ?? or does someone have a better sulotion ??
i have no knowledge in electronics.. i only love to diy those circuits.. and when i do - they work !!
but i need definite answers with clear schematics.
*** in this circuit - where should i put a FUSE ? and which one ?
hi airmailed,
The PSU you have sounds quite neat. Pity the connectors are the same as midi. I guess you could rewire the plug with some low cost unusual multipin plug/socket if you want to be really safe. You can then disregard the need for power in protection as it will be impossible to plug the wrong thing in!
Its easy to check if it’s unregulated: under no load the output will be about 20% higher than rated, and at full load the voltages should be fairly close to the designated voltage.
If the voltages are within 0.5 Volt of the designated voltage under no load then you can assume that they are regulated and therefor you should bypass rectifiers and voltage regulators on the core and other circuits.
btw: the thing that makes voltage regulators get hot is when the input voltage and load current is high.
cheers
thanks Duggle… all sounds pretty clear… my only concern with unusual connectors is not being able to find replacements… i guess i could buy 10 plugs and 10 sockets… plenty of spares i tend to worry about this kind of thing… i was looking at usb sockets the other day… it said they were good for 5000 mate/unmate cycles… i didn’t think this was many.. then worked out this would be good for plugging and unplugging 8 times a week for 12.5 years… should be enough i think… then the sockets can always be replaced…
Perhaps go to local electronic store where you can browse for a plug/socket combo that seems suitable. The one near where I live is Dick Smith (.au). and they have a wide variety of connectors even though theyre really a consumer product retailer. There are various DIN plugs/skts with various numbers of pins and I’m confident they’ll be on sale for a long time to come.
@rasOfir
My recommendation is that you purchase a cheap 12VAC 1A plug pack and follow the circuit that was posted in this thread. It’s cheap,neat,safe,elegant solution based on absolutely tried and true methods. If you are still confused or run into trouble along the way we can help in this thread (I promise!).
cheers
thanks for the answer !
few last questions (i hope)..
what should be the voltage of c1-c6 ?
c7 + c8 seems to be ceramic caps. but show a “+” on one leg.. what does this mean ?
where should i put the fuse and which ?
