Help with PSU.

[3nity]

I'm using 12-0-12 toroidal in series that puts out 24V ac...
After the bridge its putting like +35V..
The PSU is a Peter C Green PSU to work in the FEtboy/neve +24V.

Now whats the best way to drop the voltage down?

Put a resistor on every lead before the bridge or only one resistor after the bridge?

 

[Ptownkid]

didn't matta cover this around here somewhere?

 

[3nity]

It wasnt MAtta but Matt (fucanay)....
But the 10R in series after the bridge its burning after some time...

Now i wonder if it wouldnt be better before the bridge.

Thanks.

 

[shabtek]

using lm317/337 regs--look@data sheet.
change either the 220 or 2k resistor--maybe put a trimmer in parallel with w higher value to dial in (with load)
dropping with a series (high watt) R is not the way to go when you've got an adjustable reg right there

 

[3nity]

Well the Datasheets says that a 40V differential voltage is alright....i dont even reach 20V differencial...

Shabtek you mean to leave out the 2 x 2K resistors and put a trimmer in there? like a 10K maybe?

I was thinking to put in a big heat sink...

My mind is fried..?

 

[shabtek]

the ratio(?) of the 2 R determines V...'tis how mnats does it http://www.geocities.com/m_natsume/psu.html

 

[3nity]

What if i change the 220R to 120R and the 2 x 2K to a 2.2k?

What i have right now its a 220 and 2 times 2K...

I have a 24-0V-24 toroidal too....hum?

Thanks.

 

[Harpo]

Hi 3nity,
changing the voltage setting resistors will not matter, as your load is always connected and min.current draw for your regulator is within speccs.
With 4K/220R or 2K2/120R your target voltage will be nearly the same, but a 2K2 will need a higher rated (0,5W should do) resistor than your 4K.
For burning the voltage difference between raw DC after the rectifier and (24V target voltage + min.3V for the regulator=27V) at an assumed load of 240mA for 2 FETboys, this resistor should drop ~3V if your line voltage might be 10% low (or ~10V if line voltage is 10% high), so use a max.12R (for 10% low line voltage) rated for at least 2,33W (for 10% high line voltage). A bigger heatsink should do the same. YMMV
regards

 

[3nity]

What should i do if i power more pres ? lets say 4 FEtboys? then the 12R resistor is just is sucking too much current!?

 

[Harpo]

for assumed 0.5A for 4 FETboys (just measure one unit with mic and load connected), this R decreases to 6R for dropping 3V, rating will be at least 4.9W.

 

[Moby]

What should i do if i power more pres ? lets say 4 FEtboys? then the 12R resistor is just is sucking too much current!?

If you need 6R and already have 12R you can simply add one more 12R in parallel with first one. Double the wattage half the resistance