9VDC power supply parts and design questions

[Dr Ron]

I picked up a "regulated" 12VDC / 3A power supply (4CB), but it turns out to be a transformer, two diodes, two 4700µF caps and a lamp (MB318). The output measures 14VDC, and there's no regulation.

I'd like to change it into a regulated power supply for my effects pedals and am considering putting in a pair of boards with the LM3317T 1.5A regulators based on the Small Wart design:
http://www.smallbearelec.com/Projects/SmWart/SmWart.htm

I'm going to leave out R4 and LED1 since it already has a 125V led and switch.

I have some questions.

Would it be advisable to leave out the bridge rectifier (and wire the DC from the power supply)?
Should I also leave out C1 (1000µ)?

How many output jacks is reasonable?
(I was thinking about 2 regulated and 1 variable per board)

Wiring and grounding is the next question. The 2-prong AC goes to the transformer primary.
Two red wires from the center of the transformer go to the +DC, along with the two 4700µ caps.
The -DC goes through the MB318 to two diodes into the transformer secondaries.
There's a resistor across DC+ and DC-.

For grounding, I'd put in a 3-prong plug and ground the chassis, along with the center leg of the regulator.
(I suspect that the wiring is not correct. The diode direction needs to be reversed and connected to DC+, and those red center wires get connected to DC- and ground).

What are modern part numbers for the output jacks?
Mouser 163-4302-EX (Kobiconn) states "Mouser will no longer stock this product.", although they have 45,424 in stock.

And, what part number is for the cable ends?

Thanks!!!

PS
The 7809 9V regulator is a lot simpler.
Maybe I could put in a 7809 and a LM3317T for the "dead battery" option.
http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=135&Itemid=26

[iaresee]

I picked up a "regulated" 12VDC / 3A power supply (4CB), but it turns out to be a transformer, two diodes, two 4700µF caps and a lamp (MB318). The output measures 14VDC, and there's no regulation.

Stupid question time: did you test it with a load attached? Or did you just stick your probe ends against the  + and - terminals on the supply? If the latter: try attaching a small load and then taking your measurement. Power supplies will often float higher when not loaded down.

Would it be advisable to leave out the bridge rectifier (and wire the DC from the power supply)?
Should I also leave out C1 (1000µ)?

You definitely don't need the bridge rectifier -- you already have DC coming off the transformer. I'm assuming you're just going to take the output from the +/- terminals of the supply. Or are you looking to just try and reuse the transformer in the supply and throw away the rest of it? Where are you trying to graft in your regulated circuit?

C1 turns the full wave rectified output from the bridge rectifier into something that looks more like DC -- it has a little ripple in it, but it's almost steady. You probably don't need it. But you may need something across your DC output if it's really noise to smooth it out. I'd drop it and add it back in only if you need it. Again...assuming you're using the outputs on the power supply, not just the outputs from the transformer in the power supply.

How many output jacks is reasonable?
(I was thinking about 2 regulated and 1 variable per board)

I'd leave yourself a good guard band for the power supply. It says 3A, I'd spec your outputs for no more than 2A total personally.

I'm not even going to try answering the rest...I'm not sure...play safe though.

Wiring and grounding is the next question. The 2-prong AC goes to the transformer primary.
Two red wires from the center of the transformer go to the +DC, along with the two 4700µ caps.
The -DC goes through the MB318 to two diodes into the transformer secondaries.
There's a resistor across DC+ and DC-.

For grounding, I'd put in a 3-prong plug and ground the chassis, along with the center leg of the regulator.
(I suspect that the wiring is not correct. The diode direction needs to be reversed and connected to DC+, and those red center wires get connected to DC- and ground).

What are modern part numbers for the output jacks?
Mouser 163-4302-EX (Kobiconn) states "Mouser will no longer stock this product.", although they have 45,424 in stock.

And, what part number is for the cable ends?

Thanks!!!

PS
The 7809 9V regulator is a lot simpler.
Maybe I could put in a 7809 and a LM3317T for the "dead battery" option.
http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=135&Itemid=26

[Dr Ron]

Yes - I did measure the voltage without a load.

I'm thinking about the following circuit.

[jakehop]

Make the fuses bigger - 50mA is 50mA, whether 9V or 250V. I would also use a transistor with the 9V regulator, to get the full current out. 9V is what's the norm, and with a 2-3A 9V supply (depending on what you're pulling from the 317) you can power everything from an AKAI HeadRush-sampler unit, to a thousand fuzz'es :-)

Kind regards, Jake

[Pushtone]

You definitely don't need the bridge rectifier -- you already have DC coming off the transformer.

.


AFAIK all transformers output AC voltage at their secondaries.

You will need a bridge rectifier between the transformer and the filter/regulator section.
Either 4 diodes or an IC recto.

Dave

[iaresee]

You definitely don't need the bridge rectifier -- you already have DC coming off the transformer.

.


AFAIK all transformers output AC voltage at their secondaries.

You will need a bridge rectifier between the transformer and the filter/regulator section.
Either 4 diodes or an IC recto.

Dave

Yea, but he said it was a DC power supply -- it's already doing the rectification. Until he posted the schematic it was unclear that he was just looking to reuse the transformer from in the supply.

Personally, I just would have split the DC output from the transformer to a couple of regulated outputs with some protection fuses and called it a day. Why undo what's already done?

[composition4]

Make the fuses bigger - 50mA is 50mA, whether 9V or 250V. I would also use a transistor with the 9V regulator, to get the full current out. 9V is what's the norm, and with a 2-3A 9V supply (depending on what you're pulling from the 317) you can power everything from an AKAI HeadRush-sampler unit, to a thousand fuzz'es :-)

Kind regards, Jake

Not really...  50ma @ 250V on primary side of a transformer theoretically = 1389ma (1.4amps) on secondary winding.  Or ~650ma for a 120v transformer

Pretty sure that's right, someone correct me if I'm wrong though..