Re: why wall warts?

[Doug Tapia <dtapia@unoco.edu>]

>No, that's not really true. Only if the person designing the supply has no
>idea what they are doing. How many pro studio consoles have you noticed
>using wall warts? Designing clean internal supplies is not that expensive,
>and not that hard. A correctly designed supply should not increase noise 
>at
>all.
>
Actually, many of the consoles I've worked on do have external power 
supplies, though I will admit, not of the wall wart or line lump variety. 
 In fact, I would venture to say most of them have large 2 or 3 u rack 
mount power supplies.  Are there some other components tucked away in 
here besides transformers etc, or is this just a big rack mounted wall 
wart in a sense?  I'm not being sarcastic, I really don't know as I've 
only been involved in installing a couple studio consoles, but I have 
worked on quite a few and have spied power supplies for the consoles in 
many of the machine rooms.

Some of my electronic engineer friends say that transformers are 
inherently noisy.  They also point out a number of the new affordable 
Lexicon products as good examples of circut design.  (All of those 
products which use wall warts)  Aparently, all the power supply caps are 
on the main board and the wall wart only contains a step down 
transformer.  They have explained that this greatly lowers the noise 
floor.  Is Lexicon (and a number of other manufacturers, for that matter) 
just passing off sloppy circut design?  Are these engineers just ganging 
up on us?  HELP!  Any word from you, Kim, would be most enlightening.

>If anything, wall warts are a far worse situation, since they are 
>generally
>made with cheap transformers, completely unshielded in a plastic housing.
>They radiate like mad, and can cause a lot of hum in nearby audio devices.
>
>>4.  Devices with internal power supplies have to be tested for UL
>>listing, which is a pretty expensive undertaking from any perspective.
>
>It's actually pretty easy, just some paperwork if you do the design right.
>Same with CE. That's hardly a justification for using an extremely
>unreliable component in pro gear. It's more like an excuse given for lazy
>or inept engineering. For god's sake, toasters and hair dryers get UL
>approval for direct AC connections. This is electronics 101, no rocket
>science necessary!
>
I've heard people in R&D depts. (and certification managers) explain that 
if you sell a million toasters the UL listing is a few cents on a 
product, but if you sell only a few thousand Jam Men or Vortecies your 
cost per unit is much higher.  Again, have I been played for a sucker by 
Corporate America?

HELP!



-Doug