[Galen]

Hi.

I am going to design my own case for soon to be completed millett and I have some questions concerning the distance needed between amp board and PSU unit.

case 1)
some wallwart pleugged into a wall and TREAD in same case with amp. Is there any matter of how far they are from each other, giving that theres no transformator used in TREAD.

case2)
Wallwart taken apart and nicely put into the same casing with amp, incoming voltage is straight from wall. Giving that there most probably is a transformator, what would be a safe distance between PSU and amp board, so that there would be no noise generated by PSU? Between the PSU and amp is probably TREAD. depends on what kind of wallwart I decide to get.

And yes, I know that case2 is somewhat more dangerous, giving that the voltage coming in is higher but in my mind this is somewhat neater and cleaner and more compact when I dont have couple the amp with wallwart but can use regular wire coming from the wall.

Amp board itself is about 10x16cm, so I was planning something like 20x32 or so case, is that big enough? or should I go to something like 20x48 ? Might look weird then, tho.

So, any ideas, what would be the safe distance so I wouldnt get any audible noise into the amp from PSU?

 

[MisterX]

1) As long as you are not right on top the amp's inputs I doubt you would be able to hear the effects of having the tread right next to the amp board.
Measuring the difference is a different thing altogether though.

2) Why would even mess with taking apart a wall wart when an off the shelf transformer is cheaper and easier?
Aside from that I don't think anybody can answer your question unless we know exactly what transformer you are planning on using and even then it would be a best guess kind of thing.
Since you are making your own enclosure I would suggest putting the entire PSU inside it's own little enclosure within the enclosure.
Problem solved.

 

[tomb]

Quote:

Originally Posted by MisterX ... snip ... 2) Why would even mess with taking apart a wall wart when an off the shelf transformer is cheaper and easier? ... snip ...

Honestly, no offense intended, but I keep seeing similar statements. However, it appears to me that walwarts are much cheaper than basic transformers. The best may be a 24VCT split bobbin at Jameco for about $2.50. Even then, by the time you count enclosure, fuse, wire, and plugs, an AC/AC walwart for $5 - $10 ends up cheaper.

On the original question, the concern from "Case 1)" - the TREAD in the amp - is the ripple still present in the AC leads from the walwart socket to the TREAD board inside the amp. Ideally, the TREAD should be mounted right next to the backplate, so that these wire leads are of trivial length. As MisterX implies, this should all be positioned on the other side of the backplate from your RCA audio inputs. Many people do it this way, and no one complains of any interference.

There is also a "Case 3)" - putting the TREAD inside the walwart, strapping it on the back of the walwart, or splicing in a separate brick a foot or two from the walwart. The best scenario, but the most difficult, is building your own walwart.

Jameco sells walwart enclosures with ready made wall plugs and strain reliefs for the wire leads/adapter plug. It looks like the split-bobbin transformer mentioned above would fit for an inexpensive choice. There may also be room for the TREAD. Unfortunately, the Jameco enclosure is not as convenient as it should be - no documentation and a design that requires gluing the shells together. You can drill holes in it to use screws, but it's not a clean option. Some (including me) are doing that with a toroid for the SOHA amp, but that power supply is so special that an off-the-shelf walwart is impossible. The toroid also prevents it from ever being the cheap option.

Similarly, some have purchased regulated AC/DC walwarts and taken them apart. After removing the typically low-quality regulator circuit, that may leave enough room to put a TREAD back in. This is probably only a good strategy with surplussed, discounted walwarts, though - you can never guarantee that this would work until after you've cut one apart.

 

[psilosome]

Quote:

Originally Posted by tomb Similarly, some have purchased regulated AC/DC walwarts and taken them apart. After removing the typically low-quality regulator circuit, that may leave enough room to put a TREAD back in. This is probably only a good strategy with surplussed, discounted walwarts, though - you can never guarantee that this would work until after you've cut one apart.

For reference, mono gave a nice example of this approach in this thread, with links to detailed pictures (it this case the donor was a strange battery charger wall-wart).

I finally got around to modding one of my $3 walwart chargers based on that method and spare 8V regulator - it worked out nicely though I have yet to put it under load or test it with my almost-almost-done LNMP. Nothing got too hot and the voltage looked steady. I hope to use it to drive an Alien DAC. The transformer in that charger isn't good for much current - something to consider when modding a wall-wart.

 

[Galen]

Thank you for your answers and recommendations, I'll take them under consideration when I start designing case

 

[mono]

Quote:

Originally Posted by psilosome For reference, mono gave a nice example of this approach in this thread, with links to detailed pictures (it this case the donor was a strange battery charger wall-wart).

Those ratshack warts were a good deal for the ~$3 (or whatever it was) but ultimately I moved on to a more generic approach, that fits in most AC-DC unregulated warts (no need to be a giant wart as many regulated types are, but must be at least 1.75" inner cavity width to fit the board). I used a home-etched board, but it shouldn't be too hard to do similar on a piece of perfboard instead.