Bleeder resistor!

[pacificblue]

You could connect a relay with AC coil to the transformer secondary. The NC contact would connect the resistor to the rail.

transformer on = relay on = NC contact open = resistor not connected.
transformer off = relay off = NC contact closed = resistor connected.

The relay voltage should be similar to the transformer secondary voltage. Exact matching is not necessary, because relays usually have a wide working range. Depending on the model 20-30% below nominal voltage is good enough for them to operate.

Alternatives would be to
- use a relay with DC coil and dedicated rectifier on the transformer secondary. Maybe add a small smoothing capacitor 1 µF/mA as a nice-to-have.
- use a relay with mains voltage AC coil parallel to the transformer primary.
- connect the resistor through an auxiliary NC contact on the main switch instead of a relay.

[AndrewT]

Hi,
is it the capacitors you require to be discharged quickly or the music to mute quickly?

You've seen the suggestions for discharging the capacitors.
How about adding an instant OFF mute to the input of the power amp?

[kaos]

You don't mention your rail voltage, but if it's around 27V put in some 560 ohm 5 W resistors across the caps, and similar to what AndrewT said, put a simple mute circuit on the ouput of the pre-amp. Switch the pre-amp off, the music mutes, and the 560 resistors help to pull down the power supply caps in the PA.

[lhwidget]

That's a great idea Andrew, Pacificblue, & Kaos. I think I'd use a 125 VAC relay connected to the power switch. Seems easier to find than any odd AC voltage relays. Use a 4 pole/double throw relay...

For AC Power off:
1) Open the mute voltage supply
2) Short the V + rail with one 400 - 600 ohm, 5 W resistor
3) Short the V- rail with another 400 - 600 ohm 5W resistor.

My small 9400 µF filter bank caused no heating in a 450 ohm 5W resistor I used to discharge the caps by hand while I was building my amp. I mean by touch, I could not feel the resistor get warmer. My point is, I think 500 ohm/5W resistors are plenty big, even for 20000 µF filter banks, if used with a relay.

[pooge]

Relays very often come in double throw variety. You can use the "on" energization to short out input surge-reduction resistors via the opposite contacts.

I would not bring a signal line near such a relay, though. Could pick up some 60Hz noise or switch contact noise. Make sure the energization coil is powered after the fuse.

[lanchile]

Thanks guys but, I will leave alone.I just turn off the source first.