Re: Humming amps :(

["Matthew Norman" <mafiu@xxxxxxx>]

Thanks Keith, very useful.  I assume that I would be looking for exact
replacements (ie same type/voltage and capacity?)

Whats the correct way to discharge caps before working with them?  Is the
best way just to short them out with some metal thats insulated where you
are holding it or is there more of a refined method?

Matthew

----- Original Message -----
From: "Keith Doxey" <ukha@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Sunday, July 13, 2003 5:22 PM
Subject: RE: [ukha_d] Humming amps :(


> Hi Matthew,
>
> Depends on the construction of the amp but they will be reasonable
large
or
> very large.
>
> Could be "Can" type electrolytic capacitors fixed to the
chassis with a
> bracket that grips the body, could also be Radial or Axial
electrolytics
> mounted directly to a PCB.
>
> They will normally be > 4700uF with a working voltage > 50V DC.
A
> conventional linear power supply consists of...
>
> MAINS > Transformer > Bridge Rectifier > Smoothing Capacitors
> Regulation
> (optional)
>
> Apart from a persistant background hum, another sign of failing PSU
Caps
is
> that the amp no longer seems as punchy and will clip more easily on
> transients because the power supply has less reserve power to cope
with
the
> peaks.
>
> In one of my homebuilt amps the main smoothing capacitors are 22000uF
100V.
> Playing it at normal listening level in the lounge I can turn the
power
off
> and it will keep playing for about 20 seconds. Thats what you call a
power
> supply!
>
> Keith
>
> www.diyha.co.uk
> www.kat5.tv
>
>
> > -----Original Message-----
> > From: Matthew Norman [mailto:mafiu@xxxxxxx]
> > Sent: 13 July 2003 12:35
> > To: ukha_d@xxxxxxx
> > Subject: Re: [ukha_d] Humming amps :(
> >
> >
> > This is interesting - I've had similar on my amp for a while.
> >  What sort of
> > caps are we looking for?  I assume they will be in the psu
circuit
> > somewhere?
> >
> > Matthew
> >
>
>
>
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