Re: Mains conditioners and power cables
- From: "Arfa Daily" <arfa.daily@xxxxxxxxxxxx>
- Date: Thu, 01 Sep 2005 01:36:46 GMT
"Tim Martin" <tim2718281@xxxxxxxxxxxx> wrote in message
news:JM5Re.10$4T3.9@xxxxxxxxxxxxxxxxxxxxxxx
>
> "tony sayer" <tony@xxxxxxxxxxxx> wrote in message
> news:kK6asZBDNEEDFwzi@xxxxxxxxxxxxxxx
>
>> A very useful upgrade to an old amp like a QUAD 303, replacing the main
>> smoothing caps and output ones with modern electros which give more mfd
>> for the space.
>
> In general, you have to be careful increasing a power supply's
> capacitance;
> it will reduce the ripple, thus reducing the amount of time the charging
> current flows, thus increasing the charging current.
>
* I'm having a bit of trouble with that one. A larger capacitance will
certainly try to increase the * initial charge current over the first few
cycles as the power supply comes up, which if allowed, * may exceed the peak
forward current capability of the rectifier diodes. However, in a
* transformer derived supply, the effect will be mitigated by the natural
current limiting effect of
* the transformer's secondary and to a lesser extent, primary, winding
inductances. Any
* resistance in the windings, or in the form of surge limiter resistors,
will also contribute to the
* charge current limiting.
* Once the capacitor is charged, the ripple will be reduced by the
effectively lower source
* impedance of the increased value of capacitance. This effectively means
that the capacitor is a * bigger bucket, better able to supply the load's
current requirements, which haven't changed
* from when a smaller value was fitted. This, it only needs to do, of
course, between cycle
* pulses from the rectifier. As the bucket won't drain down as far during
these pulse gaps, it will * take less energy to fill the bucket back up, not
more.
> This could result in exceeding the diode ratings, and may also increase
> hum.
>
> Tim
>
>
* I've never heard an increased value resevoir or smoothing cap, actually
increase hum level.
* Another point in favour of replacing with more modern capacitors, is that
with the current
* tendecy to move towards switch mode power supplies, much better types are
now available, * sporting improved leakage characteristics, ESR, ripple
current capacity, HF performance, and * finally, temperature rating.
* And of course, as Tony said, more muffs per cc
* Arfa
.
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