[[email protected]]

Scott Dorsey wrote:

===================

But I would assume the bulb lighting up initially, is due
to the initial in-rush current, that charges up the electrolytic
filtering caps, on the outputs of the rectifiers?

No. This is a "power-on thump" which is caused by the coupling capacitors
charging up, not the power supply.


** The OP never mentioned any " thump" and is not talking about one.

It's made much worse with amplifiers that run on a single supply rail, so
the output of the power amp stage is sitting halfway between the supply
rail and ground during normal operation. This means there is a huge
coupling capacitor from the output stage to the speaker and that has to
charge up. While it is charging up, the woofer coil will bottom out.


** Nonsense, speaker output electros ( rarely seen in the last 30 years) do not do that, they charge slowly.

I = C.dv/dt

if C = 2000uF and the cap charges to 30V in 0.5 second, I = 120mA.

To " bottom out " a woofer a takes several amps.

Well-designed amplifiers have a protection relay that cuts the speaker off
when there is any appreciable DC offset. It will sometimes take a little
time to stabilize because of the turn-on thump.

** Direct coupled amps sometimes have such relays, a great many do not and don't need them.

In most cases, a simple muting FET between the pre and power stage does the job.


.......... Phil