I was thinking of the 4700uf
I have on the input to both the regulators.
May not be visible in the photos.

I have this police scanner and if i do not
put this big filter cap on the power
coming into the scanner will get hum
from just about any power module i use.

I think these AC to DC 120V to 12V converters are filtered
with unsersized caps as well as not regulated.
60 HZ (small but there) gets through to the circuits
accepting such power.

Thanks for your clarification.

I believe the larger caps do no harm
yet in addition you need what is specified
by the manufacturer.

It seems you need to gang capacitors ever smaller
in factors of x10 (f/10) to filter properly
due to component ideosynchracies.

The kits from DIY came with the installed caps
as well as unnessesary other components
such as FW bridge rectifier for AC input.
I have modified these circuits to suit my own desires/needs.

I wonder if cascading regulators would knock down
any 60Hz hum ?

I once plugged a radio accidentally into 400Hz 120V and
it ran beutifully. even tho the wall plate was red.
Let it run an hour or so while relaxing aboard ship.
I think it was a power outlet for the electronics technicians
to work on special equipment.
400Hz must filter out well.

Regards,
geoff

----- Original Message ----- 
From: "Dave Nelson" 
To: 
Sent: Thursday, July 14, 2011 11:17 PM
Subject: Re: Noise


> Geoff,
>            What Blair is saying, and I agree,  the 470uF caps on the 
> outputs of the
> voltage regulators are way too high.  As he said  the norm.is ~ 10uF
> and keep the 0.1uF caps in parallel with them
> 
> cheers
> Dave
> 
> 
> 
>>Hello Blair,
>>
>>I always put the largest capacitors on the input side of the regulators,
>>This way when power is cut and the voltage dies, the input should always 
>>be a higher
>>voltage than the output so i do not worry about loss or upsets
>>to power. I have not yet in many years lost an Opamp
>>to lightning so being worried about RFI like always
>>i do not want any diodes near the input.
>>Because you use caps like this should have fuses
>>but since these wall converters are protected internally
>>(so i understand) I do not worry about shorts.
>>caps have a nasty tendency to short when they go bad.
> 
> 
>>----- Original Message ----- From: "Blair lade" 
>>To: 
>>Sent: Tuesday, July 12, 2011 2:24 PM
>>Subject: RE: Noise
>>
>>Geoff,
>>
>>SNIP
>>
>>A note about power supplies, the 470ufd caps after the regulators are 
>>probably a bit big, National Semiconductor suggest around 10ufd with 
>>0.1ufds in parallel and you really should have reverse diodes across the 
>>regulators with capacitors this size (see National Semiconductor's 
>>application notes for the reasons).
>>
>>Bypass every chip and every board with 0.1ufds on each rail ( to the local 
>>board ground) and typically 1 * 10ufd on each rail to ground on each board 
>>if the supply leads are greater than about 6 inches.
>>
>>blair
> 
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