I agree to some extent, but he does state the frequency changes according to which modules are being used, which means it doesn't match the mains frequency

On 7 Jul 2013, at 19:20, "anoop.sahal" < draks@... > wrote:

>
>
> I think all coil based voltage transformers will emit noise. It is often due the coils attracting and repelling one another at each voltage cycle change.
>
> Winding them tightly helps initially but the coils lengthen as they age and they loosen up. Varnish helps delay the loosening by binding the coils.
>
> Is the hum mains frequency matched
>
> That would indicate that the above case is likely.
>
> I have only known solid state transformers not to hum.
>
> i would mount the PSU boards on Rubber washers to minimise making the case a sound box.
>
> Any concurrance
>
> Regards Anoop
> --- In Doepfer_a100@yahoogroups.com , "isoldeandisobelle" <isoldeisobelle@...> wrote:
> >
> > Hi - Thank you both for your replies.
> >
> > I am not sure what you mean by ''mechanical'' but, the sound is coming from the transformer itself. It is not too loud but I can hear it from a short distance away. The earth cables are all connected properly. My other 6U case is connected to the exact same power supply and makes no noise - this is what concerned me
> >
> > --- In Doepfer_a100@yahoogroups.com , Florian Anwander <fanwander@> wrote:
> > >
> > > Hello
> > >
> > > I assume you mean a mechanical hum. Right If so, then it should be
> > > related to the method how the powersupply is fixed to the housing.
> > >
> > > Florian
> > >
> > >
> > > On 07.07.13 00:31 , isoldeandisobelle wrote:
> > > > Hi gang -
> > > >
> > > > I have a 6U case and a 9U case, the 9U PSU hums (which changes in frequency when different modules are in use.) - the 6U does not do this.... is this ok
> > > >
> > > >
> > > >
> > > > ------------------------------------
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > >
> >
>
>


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