[Zorander]

I'm thinking of building one such PSU to power my SuperDAC (I have one built for me previously and I would now like to try my hands on building another one, preferrably with my choice of select components). A quick brainstorm reveals I will need the following, as a basic:

1) Enclosure (plastic or metal is recommended?)
2) Transformer (lots of questions: toroidal or otherwise? Any specific output figures I am looking at?)
3) Wires (what gauge size for the output? Should I care about differences in metal types?)
4) Thinking of incorporating an input jack so I can plug my own power cables; Is one with built-in power filter recommended for this purpose?
5) How to properly mount the transformer?
6) (add any other crucial stuff I am missing out here).

Cheers and TiA!

 

[ericj]

Mounted far enough from the audio circuit, an EI-core transformer will be less noisy than a toroidal transformer.

Mounted close to the circuit, the toroid has a smaller magnetic field, so you won't get the 60hz tone so much, but it won't filter out as much common mode noise as the EI-core naturally does.

I'd stick an EI-core 9v trafo in a jameco wall wart box with a simple three-capacitor filter on the mains, but I'm a cheap person.

 

[Zorander]

By EI-core, do you mean the transformer in the picture below (the one with multiple-coloured wires connected)?

Edit: Is something like this good?
Edit 2: Is a fuse necessary with these applications?

 

[Bjornboy81]

Quote:

Originally Posted by Zorander /img/forum/go_quote.gif 1) Enclosure (plastic or metal is recommended?) 2) Transformer (lots of questions: toroidal or otherwise? Any specific output figures I am looking at?) 3) Wires (what gauge size for the output? Should I care about differences in metal types?) 4) Thinking of incorporating an input jack so I can plug my own power cables; Is one with built-in power filter recommended for this purpose? 5) How to properly mount the transformer? 6) (add any other crucial stuff I am missing out here).

1. doesn't matter metal or plastic other than astetics.

2. I agree with Eric for the XFM (except the common mode noise rejection property part...)

3. You didn't give what current draw you'd be seeing. If an amp or so, 16 gage is more than enough.

4. I don't nessasaraly agree with input filters. Those things filter high frequencies (100KHz and up) which aren't even audiable anyways. Just a waste of money

5. Like the one you linked to, just mount by the tabs provided. You can always mount on rubber pads to reduce vibrations too. Toroidal XFM's mount via center screm hold-down.

6. Why not use a Wallwart?

 

[Zorander]

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif 3. You didn't give what current draw you'd be seeing. If an amp or so, 16 gage is more than enough.

I am looking for current draw capability of 2-3 amps at minimum.

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif 4. I don't nessasaraly agree with input filters. Those things filter high frequencies (100KHz and up) which aren't even audiable anyways. Just a waste of money

Good to hear that. I bought one previously (just threw it into the shopping basket out of curiosity and never even used it) so if it does not actually harm the sound, I might just use it.

Do I actually need a fuse to build a PSU?

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif 6. Why not use a Wallwart?

I have not been able to find any off-the-shelf PSU that outputs 9VAC with at least 2-3amp output.

I will compile a list of 'raw ingredients' that I will need to build these and hopefully you guys will help me refine that.

Cheers!

 

[error401]

Quote:

Originally Posted by Zorander /img/forum/go_quote.gif Do I actually need a fuse to build a PSU?

Absolutely. It's a tiny investment considering it might save you a fire that could destroy your home or your gear. Consider that most audio gear will draw less than 5A, but most home circuits allow 15A or more before they trip. 10A is clearly a fault condition, maybe an intermittent short or something, but won't trip the breaker. Certainly has the potential to start a fire or at the very least destroy your gear...

Fuses are not optional.

Am I the only one that thinks needing a 9VAC supply at 3A is strange? If it's audio gear, it's going to be DC internally (unless it's a tube heater or something). Furthermore, all you need for an AC supply is a suitable transformer, there's not much else you can add to improve the quality or whatnot - all the options there are in the rectification and DC regulation side of a normal supply. The only concept of a real AC power supply I can think of would be rectifying to DC and then recreating the AC voltage from the DC - far more complicated than you need.

You're probably having trouble finding off the shelf parts because there's not really any use for them. A 3A trafo is going to be fairly large for a wallwart, and most wallwarts have gone to switched mode anyway. Any real product needing such a large AC supply would build a bare transformer into the case - but even that is strange. Most applications nowadays require DC.

If you really need that much current at AC, just grab something like DigiKey PN 182K9-ND and put it in a case with a fuse and optionally a line filter.

 

[regal]

Channel Island has no trouble charging $150 for a 14V AC powersupply. There must be something we're missing.

I thought line filter capacitors smooth voltage spikes from your 110VAC.


Another thing is you better make sure your device really draws 3 amps. If you use too big a transformer it could put out too much voltage (since it will be near idle). Your internal regulators could overheat and fry.

 

[Bjornboy81]

Both Error and Regal make great points.

Always fuse your power sections!!! A good bet is to go with 125-150% of what your nominal current draw is. if it's 2 amps go with a 3 amp fuse.

Like Regal said, you have to consider regulation of the transformer. Many are rated at a certain voltage, 15Vac lets say, but will swing 15% or better making as high as 18V or so. Just be aware.

Regal, yes line filter capacitors between line and ground will shunt transients to ground, but typically the ones he's talking about are designed to reduce 100khz, 1mhz and up. It won't hurt to put it in though.

Yeah, the value of 9VAC @ 3A or more sounds strange. Double check those numbers.

 

[ezkcdude]

Quote:

Originally Posted by Zorander /img/forum/go_quote.gif I'm thinking of building one such PSU to power my SuperDAC (I have one built for me previously and I would now like to try my hands on building another one, preferrably with my choice of select components). A quick brainstorm reveals I will need the following, as a basic: 1) Enclosure (plastic or metal is recommended?) 2) Transformer (lots of questions: toroidal or otherwise? Any specific output figures I am looking at?) 3) Wires (what gauge size for the output? Should I care about differences in metal types?) 4) Thinking of incorporating an input jack so I can plug my own power cables; Is one with built-in power filter recommended for this purpose? 5) How to properly mount the transformer? 6) (add any other crucial stuff I am missing out here). Cheers and TiA!

I'm not sure if this suggestion would help you, but there are plenty of wall wart transformers out there you could use. I use a 12VAC wall wart and then feed it to a dual regulated PSU board for my DAC.