ROLAND AMP 9V SUPPLY

[deadastronaut]

hi guys i have a roland micro cube amp...

the supply got dropped and the earth pin on the uk plug has busted (though not connected internally)

so am now going to rehouse it...with a uk plug and dc out...(as the housing has cracked i opened it up)

my question is this.

this power supply on my roland is nice and quiet utterly silent in fact, with the amp, and all other 9v devices

all it is, is a transformer, a 1000uf . 25v cap
and 4 diodes/rectifier...thats it.

so nothing special at all inside..


when i try other good supplies on the amp that work with pedals, /
pedals boards etc fine, it has a noticable 60 hz hum on the amp.....weird.

so what is so special about this very basic official roland supply compared to others???  (without cracking open all my other supplies obviously lol)

just curious. 

edit: the roland is 9v 500ma  4.5va

[antonis]

60 hz hum

Weird indeed..!!
(does London's mains supply work on its individual frequency..??) 

P.S.
Most possible humming issue is ground loops with the other "good" supplies..

[Rob Strand]

all it is, is a transformer, a 1000uf . 25v cap
and 4 diodes/rectifier...thats it.

so nothing special at all inside..

%
I'd expect that to be in 90% of filtered wall-warts with a transformer.
It's a standard wall-wart recipe.

pedals boards etc fine, it has a noticable 60 hz hum on the amp.....weird.

so what is so special about this very basic official roland supply compared to others???  (without cracking open all my other supplies obviously lol)

just curious. 

Doesn't make much sense to me either.

(though not connected internally)

Given you already know this.   You could check the others are the same.    I suspect so its virtually unheard of for generic wall-warts to connect back to the mains earth.

Also, it sounds like the problem is more mains hum than buzz.    Poorer isolation on the transformer might result in buzz but not hum.

So that only leaves the size of the size of the filter cap.   Try adding a 2000uF cap across the DC inlet.   Maybe the actual value of the Roland cap is higher.   I've got my doubts but I can't see what else will help.

Some transformers have a strong stray magnetic field and you will get hum directly from the guitar pickup.  See if you hear any hum with the guitar dialed to zero and/or make sure you aren't standing close to the wall-wart.

[anotherjim]

Roland may have paid for a low ESR cap while the others have Jelly Beans.
I've seen caps as low as 470u in some PSU.
Also, compare output current ratings. A 500mA wart will be physically smaller than a 1A and fitted with a smaller cap.

Some parts of London used to have DC power! It was provided by the generators for electrified railways which used DC - and still do although it now comes from the AC grid.