Advice: build one box to replace all my wallwarts?

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Freq Band

Well-known member
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Jan 5, 2006
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608
Location
Electra City
I've about 25 wall-warts powering various audio effects...7.5vdc, 9vdc, 12vdc, and some 9 & 12vAC.
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Objectives:

1) To reduce the clutter inside my rack, and beneath my DAW desk.

2) To possibly improve sound via better power.

3) One box.

4) To keep me busy for a while. :roll:
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Here go the newb questions:

a) Should I build several PSU's according to my voltage needs ?...or is there a way to use one PSU for all voltages needed ?

b) Can too much available current be disagreeable to some units ?

c) AC warts inside are just a tranny?

d) How would you approach this?

I know there might be some product out there that does this, perhaps for guitarists stomp-boxes....and there used to be a product by "Juice Goose" I think.

thx,

-=FB=-
 
Many times the independent low-capacitance isolation of a wall wart is just what the doctor ordered. As cluttery and ugly as they are (Sid Harman once told me he thought his son had "one for every test that he failed") they do serve a purpose.
 
The answers to your first 3 point are .. yes, no, yes.

Wall warts may be ugly and annoying, but it's not all negative. Having individual power supplies ensures that the equipment is isolated from other equipment, and that the power transformer is removed from sensitive audio circuits. It's unlikely that you will improve anything by making a bigger better power supply.
Yes, AC power supplies are 'just a tranny', but it is the right tranny, and it will have a thermal cutout to protect your studio from catching fire if it fails.
Keep all your 'wall warts' in a single well ventillated box by all means, and keep the box away from the sensitive stuff.
 
It is technically possible of course but:

The 25 different gadgets powered by wall-warts you have today might not be the same ones you have in 6 months time. So, will you redesign every time you get a new box of tricks?

You could make each output switchable AC/DC and variable voltage and current limiting - BUT then you are talking about a very expensive power supply.

And you'd need to get it certified or you're little power box will be an excellent reason for the insurance company NOT to pay out of there ever is a fire...

Perhaps better spend some time getting some decent power distribution strips and velcro straps and make it neat looking or hide it all.
 
Certainly these are some valid points. Thank you.
You know how, when you want to do something, and are kinda set on it because you think it's a good idea........and many people tell you its probably NOT a good idea......I've learned (thw) to listen to the majority opinion, even though it's not what I want to hear.



Here is a commercial version:
http://www.juicegoose.com/12paq.htm

-=FB=-
 
[quote author="TedF"]

Wall warts may be ugly and annoying, but it's not all negative. Having individual power supplies ensures that the equipment is isolated from other equipment, and that the power transformer is removed from sensitive audio circuits. It's unlikely that you will improve anything by making a bigger better power supply. [/quote]
[quote author="bcarso"]Many times the independent low-capacitance isolation of a wall wart is just what the doctor ordered.[/quote]

So why then, do we DIY'ers stress over building the best power supplies ? (even when they are in a seperate box)? Is there a difference, or a contradiction here?
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For the record:
Some of my commercial gear with "heavy duty" external power adapters are:

Lucid ADA1000 da/ad converter
Rane SM26b splitter/mixer (3)
Frontier Tango adat converter
...these all have the oversize dedicated PSU (large floor wart)

Much of the other small wallwart-fed gear is stuff like synth filters, midi sequencers/controllers, small synths, other low current midi stuff.


-=FB=-
 
[quote author="cuelist"]And you'd need to get it certified or you're little power box will be an excellent reason for the insurance company NOT to pay out of there ever is a fire...[/quote]

Hmmmm... I understand.... but wouldn't any of our our mains powered DIY boxes bring us already in that situation ? :roll:



So cool tip, thanks: skip the insurance, they won't pay anyway - so spend that money on more DIY !
 
Heh. Yes, as far as insurance goes, we are all in jeopardy. Remember what UL stands for, and why it exists.

As far as a contradiction about DIY overbuilt supplies and wall warts, there is none, really. The double-bobbin trafos typical of wall warts have very low primary-secondary capacitance, but you can get good results with toroids and static shields. The other prized aspect of wall warts, no less true at least in principle of other transformers, is the ability to move them away from circuitry, and take advantage of the reciprocal cubic law of near-field field strength with distance. If you have to put the transformer in the box with the electronics, mount it as far away as you can and orient it for minimum circuit pickup. If you use a toroid beware of high pulsed currents saturating the core and rendering it no longer ~self-shielding (BTW this is the reason that sometimes toroids are much larger than mere heat rise considerations would dictate).

In terms of the low capacitance aspect, I'm designing a fancy highend box that has two "floating" supplies in one section. I'm getting the power from pairs of back-to-back double-bobbin EI core trafos, with the central connection referenced to circuit common. They will be mounted in a way as to roughly cancel their magnetic field emission at a moderate distance away. The trafos will still be in the box with the electronics.

Galvanic isolation among system components may well be necessary for optimal performance, although it is an indication of design problems when it is absolutely required, especially when you are using balanced signal transmission. The convenience of a central power system is indisputable, and I suppose one could be designed with isolated outputs, and well-regulated low-noise ones at that. One could have an option of isolation or not depending on what worked better.

When I've designed products with wall warts or brick supplies I like to use a.c. out into the product and do the rectification inside, even though on the face of it this would be bringing in more line noise and hum. But the appeal is at least twofold: having the power supply bulk cap close to its load, and having an ability to sense line voltage cutoff so you have time to mute before the powerdown pops and thumps. It's also a little cheaper, and you can make decisions about the sizing of the transformer independently of the ratings printed on a.c.-to-d.c. adapters, which generally assume continuous current drain.
 
[quote author="cuelist"]
And you'd need to get it certified or you're little power box will be an excellent reason for the insurance company NOT to pay out of there ever is a fire...[/quote]

I was gonna say there are commercial units out there if you don't want to DIY. But doesn't the above statement go for ANY of our DIY gear?
 
And the companies' cost of getting UL/CSA approval ($$) for an "in-the-box" transformer......is...... :grin: ...or.... :cry: ....vs outside-the-box...a deciding factor ??

Turns out, the comercial linear warts are soon to be phased out, in favor of switch mode. Here in California, July 1st 2006 is the 'no-more-new-linear' date.

Read article here:
http://www.edn.com/article/CA6262867.html
Read a proposed regulation here (pg. 15 sums it up):
http://energy.ca.gov/appliances/2003rulemaking/documents/case_studies/CASE_Power_Supplies.pdf
Official:
http://www.psma.com/ul_files/forums/energy/cec_fact_sheet200503033.pdf

-=FB=-
 
[quote author="Freq Band"]And the companies' cost of getting UL/CSA approval ($$) for an "in-the-box" transformer......is...... :grin: ...or.... :cry: ....vs outside-the-box...a deciding factor ??

Turns out, the comercial linear warts are soon to be phased out, in favor of switch mode. Here in California, July 1st 2006 is the 'no-more-new-linear' date.

Read article here:
http://www.edn.com/article/CA6262867.html
Read a proposed regulation here (pg. 15 sums it up):
http://energy.ca.gov/appliances/2003rulemaking/documents/case_studies/CASE_Power_Supplies.pdf
Official:
http://www.psma.com/ul_files/forums/energy/cec_fact_sheet200503033.pdf

-=FB=-[/quote]

This is very interesting. I can see where it applies to linear regulators inside of bricks and warts, but I wonder how it applies to mere transformers? They are not usually that inefficient per se, although if the cores are teeny and the magnetization inductance of the primary not large there can be a problem.

It looks like a 30VA trafo, for example, would have to be itself about 80% efficient when delivering the various 25%, 50%, 75%, and 100% (full load) powers to the device it's powering. If it weren't it would be getting mighty hot anyway---that's not that big a transformer, and if the power drawn was 30W even 7.5W wuld be getting it quite warm after a while.

If you throw on a linear regulator inside the situation gets worse, even with low dropout, as at low loads the unreg voltage soars and the linear's efficiency goes down precipitously.

EDIT: I notice they do say ac-ac supplies as well. I wonder now just how good a standard decent transformer driving a cap input filter is.

2nd EDIT: I see that some pushback is occurring (see http://energy.ca.gov/appliances/notices/2006-01-19_workshop.html) but I can't find the results of it yet. Also, I see that "compact audio and digital TV adapters" are affected starting Jan 1, 2007.

I guess if you build these into the units you will be exempt for a while. It's really kind of sad---the isolation of a couple tens of pF is hard to do with switchers, especially when they are required themselves to be so damn efficient.
 
I got rid of my wallwarts in two ways...

1. if it is a wallwart-ish - ie the bump isn't on the mains plug. I cut the plug off - attach an IEC male adapter and plug it into one of four Power conditioners I have (the ones with 12 filtered IECs on the back)

2. if it is a proper wallwart - then I plug it into a 8 way board - then cut the plug of the 8 way board - put an IEC on that then plug that into Power Conditioners

The Power Conditioners are also star'd to a master Power conditioner - and only 1 physical plug goes into the wall...

The power conditioners are those Samson things with the rack light on them (10amps I think)
BTW - I am no electrician - this is what I do for fun (not plugging in IEC leads but this Audio stuff)
As you can guess - absolutely no mains hum at all...
 
Here is the latest commercial product that tries to do what you want.
http://www.mpathx.com/products.php

It looks interesting.
 
Hmmm... Not convinced by such hi-tech flummery. :roll:

Commoning up power supplies like that is really asking for trouble, and what about AC/AC wall warts?
bcarso had some highly intelligent things to say about this whole subject a few posts earlier.

Well, it will be interesting to see how the legislators fare with their 'ban the transformer' laws. :roll:
 
[quote author="TedF"]Hmmm... Not convinced by such hi-tech flummery. :roll:

Commoning up power supplies like that is really asking for trouble, and what about AC/AC wall warts?
bcarso had some highly intelligent things to say about this whole subject a few posts earlier.

Well, it will be interesting to see how the legislators fare with their 'ban the transformer' laws. :roll:[/quote]

Yeah, it seems that you could isolate each one; either using DC-DC converters or a crazy multi output transformer. The real question is whether you are getting better power.

But of course I'm not running out to buy one.
 
...But I did come across this DIY stompbox multi-psu box..."Spyder".

....complete with an option of re-winding a Magnetek's secondaries to make a many-multi-tap tranny.

http://www.geofex.com/Article_Folders/Spyder/spyder.htm

=FB=
 
One *downside* to wall warts is their reliabilty. I seem to always be chasing failures with the warts at various client sites. But, then again, I live in a "lively locale" in the springtime, with the thunderstorms, etc.

Case in point. I was going to scan some ancient API 312 app notes (per a request on another thread on this board), and discovered my HP scanner was kaput. A quick check revealed the HP's 12VDC wart was deader than a doornail! Sigh, and I always unplug all of my 'puter gear when the skies look threatening.

I see that "linear" supplies (relatively bulletproof) are going to be banned by the tree-huggers, in lieu of switchers.

Well, I kinda like switchers after a decent thunderstorm here, since I get more than a few service calls!! Many billable hours Help Put Beans On The Roth Table!

OTOH, linears seldom fail.

Bri
 
I'm suspecting that there will be a pushback on the ban on linears, especially when a plain old FeCu affair transformer is not all that inefficient. As remarked earlier, it is damn difficult to get anything like the isolation of a mere 20-30pF between mains and secondary from switchers.

BTW, although he sort of knows what he's doing, the multiple secondary trafo guy two posts up has a very garbled account of what the "ground loop" problem really consists. It is rarely the loop pickup of B fields that is the problem, although there are situations where that is important. It's mostly conducted stuff causing voltage drops that can't be separated from signals. In that respect a plurality of individual a.c.-a.c. warts or bricks with good input-output isolation is fully as good or better, other than the clutter factor, than a single master multiple-secondary trafo supply.

When you start doing the regulation inside a.c. to d.c. warts and have to determine how they are all interconnected then you can screw up if you get sloppy.

I recently ran across my sheaf of notes from an AES workshop called Ground View. I believe most of the papers were expanded and reprinted in a AES journal issue a few months later---it would be circa mid-to-late 1994. It is worth getting ahold of if you really want to understand this stuff.
 
One other bad thing about switchers (besides reliabilty of the cheap models) is the possibility of "beat" frequencies as each of the regulators generates it's own, slightly different, frequency from the others.

It hasn't been all that common, but I've solved more than a few "odd noise" problems after isolating the noise to more than one switcher (again, typically a cheapie) operating in the same system, and apparently close in operating frequency to the other "offender".

Bri
 
Confusia say... Man who want to build multi-output PSU needs to reinvestigate the initial problem.

Clutter.

So -- Just a thought - get yourself a 3U rackmount case and throw all of your Wallwarts into it along with a multiway connector at the bottom of your rack.
Then bring out each of the wallwart outputs into one strip going up the side of your rack connected with cable ties, you can then tidily bring the power jack horizontally accross to your inidividual units...

Just a thought -- why reinvent the wheel.

Cheers

R
 
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