xstnhealer wrote:Hello:
I recently bought both the AC/DC PSU and the World Transformer. I am getting 28.8 vac out of the transformer (2x12v, 30va), but I am getting odd readings out of the three rails of the AC/DC board. My set up is as follows:
Transformer AC/DC Xfr i/p AC/DC o/p
A --------------------------------- AC +V = +17.6vdc (pot all the way maxed and it starts higher then slowly decends)
B---C 0v 0v +48 = +36.9vdc (pot all the way maxed/steady)
D---------------------------------- AC [0v -------- ground]
-V = -18vdc (pot all the way maxed/steady)
I'm measuring from 0v to the appropriate rails. I have the D = doubler jumper soldered. I need +/-24vdc and +48vdc. Any ideas as to what I'm doing wrong?
Regards, Jason
HI Jason
This is covered on the thread and is the most commonly misunderstood.
First when you want +/-24vdc you should be using a transformer that has close to the same AC volts as the DC needed so 2 x 22vac to 2 x 25vac. This will make roughly +/-32vdc to +/-35vdc unregulated which after regs will trim up to +/-24v and with doubler +48v.
If you use 2 x 12vac you will get +/-18vdc unreg and max after reg of about +/-17.5vdc but it will not reg properly. So this setup is good for +/-12vdc and 48v with tripler. With Neve mod done this would make +24vdc and 48vdc but no -24vdc
If you want to use the 2 x 12vac you can but you have to wire it as 1 x 24vac with the centre 2 wires joined to themselves and nothing else (no 0v) and then the 2 end wires one goes to a AC in and the other to 0v. This will give you the +/-24vdc and 48vdc on doubler but only at 50/60Hz refresh rate as it is only half wave rectified where as 2 x 22vac will give 100/120Hz refresh rate for smoother unreg dc for the reg. This will work fine in most preamp setup with less than 500mA current draw on any rail.
Transformer 2 x 12vac
A --------------------------------- AC
B---C
D---------------------------------- 0v
WARNING since you have wound the trim pots fully open you must reset them back to roughly centre postion -12.5turns before re-powering up with rewired power transformer.
+/-24vdc and +48vdc use 2 x 22vac to 2 x 25vac 100/120Hz refresh (can use 1 x 22vac to 25vac but 50/60Hz refresh) Doubler
+/-18vdc and +48vdc use 2 x 18vac 100/120Hz refresh (can use 1 x 18vac but 50/60Hz refresh) Tripler
+/-15vdc and +48vdc use 2 x 15vac 100/120Hz refresh (can use 1 x 15vac but 50/60Hz refresh) Tripler
Simples rule to remember is AC volts should = roughly the DC volts you want regulated (not including the 48vdc pump charge rail).
eg +/-24vdc = 2 x 24vac (22vac to 25vac)