Switching off amplifier (dumb question inside)

EBM_dude · 29th January 2010, 08:34 AM

So fellas, I just thought about the following design "feat" of the amp I'm going to build. The power switch turns on the mains to the transformer which in turn powers the rest of the amp. Say I have like 50000µF of caps in the power supply. Now if I switch off the amp, the mains get cut off BUT there is still plenty of charge inside the caps that may continue to power the amp for quite a while. How can I get rid of this? I want the amp to be dead silent when I turn it off.

wwenze · 29th January 2010, 09:11 AM

Muting transistors

EBM_dude · 29th January 2010, 09:18 AM

Thanks, I got a private message that gave some insights how to do that: a set of relays that cut the power from the amp circuit as soon as the secondary's voltage is down.

Enzo · 30th January 2010, 02:26 AM

If you are looking at relays to open the power rails, why not use the relay to simply open the speaker connection?

wwenze · 30th January 2010, 03:48 AM

Quote:

Originally Posted by Enzo

If you are looking at relays to open the power rails, why not use the relay to simply open the speaker connection?

And this serves a double purpose of eliminating the on-off boom. Neat.

EBM_dude · 20th February 2010, 09:34 PM

Another dumb question. What relays should I use to prevent a possible degradation of the sound?

tomchr · 21st February 2010, 05:24 AM

You should always have a bleeder across the supply caps. A bleeder is a large resistor that will drain the charge off the supply caps. Calculate the resistor following ohms law to ensure a current through the bleeder of about 10 mA.

To avoid the turn-on/off pops, use a relay on the speaker connection. Siemens makes some good ones. As does Omron. Look for one that can switch 10~20 A with gold or silver-nickel contacts.

~Tom

EBM_dude · 21st February 2010, 10:12 AM

Yes, bleeder resistors are included in my design. Thanks for the hint on the realys! I have two Omron relays here, capable of switching 20 amps: click me! Guess they're fine then. *happy*

AndrewT · 21st February 2010, 10:19 AM

I'd suggest you look at the possibility of using input mute as well.

Then you have a number of options that can be added later.
DC detect, triggering the input mute.
Higher voltage dc detect triggering the output relay with latch that requires operator action to unlatch, eg switch off power.

EBM_dude · 9th May 2010, 12:15 AM

Good idea! 8-)

29th January 2010, 08:34 AM	#1
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	Switching off amplifier (dumb question inside) So fellas, I just thought about the following design "feat" of the amp I'm going to build. The power switch turns on the mains to the transformer which in turn powers the rest of the amp. Say I have like 50000µF of caps in the power supply. Now if I switch off the amp, the mains get cut off BUT there is still plenty of charge inside the caps that may continue to power the amp for quite a while. How can I get rid of this? I want the amp to be dead silent when I turn it off.

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29th January 2010, 09:11 AM	#2
wwenze diyAudio Member Join Date: Mar 2008	Muting transistors

29th January 2010, 09:18 AM	#3
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	Thanks, I got a private message that gave some insights how to do that: a set of relays that cut the power from the amp circuit as soon as the secondary's voltage is down.

30th January 2010, 02:26 AM	#4
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	If you are looking at relays to open the power rails, why not use the relay to simply open the speaker connection?

20th February 2010, 09:34 PM	#6
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	Another dumb question. What relays should I use to prevent a possible degradation of the sound?

21st February 2010, 05:24 AM	#7
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	You should always have a bleeder across the supply caps. A bleeder is a large resistor that will drain the charge off the supply caps. Calculate the resistor following ohms law to ensure a current through the bleeder of about 10 mA. To avoid the turn-on/off pops, use a relay on the speaker connection. Siemens makes some good ones. As does Omron. Look for one that can switch 10~20 A with gold or silver-nickel contacts. ~Tom

21st February 2010, 10:12 AM	#8
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	Yes, bleeder resistors are included in my design. Thanks for the hint on the realys! I have two Omron relays here, capable of switching 20 amps: click me! Guess they're fine then. happy

21st February 2010, 10:19 AM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I'd suggest you look at the possibility of using input mute as well. Then you have a number of options that can be added later. DC detect, triggering the input mute. Higher voltage dc detect triggering the output relay with latch that requires operator action to unlatch, eg switch off power.

9th May 2010, 12:15 AM	#10
EBM_dude diyAudio Member Join Date: Aug 2009 Location: Germany	Good idea! 8-)