RE: Humming amps :(

["Keith Doxey" <ukha@xxxxxxx>]

NEVER SHORT THE TERMINALS !!!!

You can get currents of thousands of amps which can vaporise thin metal
screwrivers and throw molten metal at you.

Use a high power resistor to discharge them before working on them.

Keith

www.diyha.co.uk
www.kat5.tv


> -----Original Message-----
> From: Matthew Norman [mailto:mafiu@xxxxxxx]
> Sent: 13 July 2003 18:09
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Humming amps :(
>
>
> 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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