Turn on delay for single-railed amp

[kubeek]

I want to mak a turn-on delay for a class-A amp, which is powered by 12V and has a capacitor on output (in series with speaker).

Can you help me make a circuit which would have cca 3sec turn-on delay and immediate turn off. The thing I need most help with is something to prevent activating the output too soon after someone switches it off and on again, probably something to discharge the timer cap or some latch.

For the immediate off I plan to use raw rectified voltage to power the relay, so when the transformer is switched off, the relay goes off too.

Your opinions?

[Rolf Zetterberg]

Here is a simple one to start with(you'll find several more with a simple Google-search!)
http://www.epanorama.net/circuits/ampdelay.html

[Nordic]

http://www.diyaudio.com/forums/showt...25#post1071625

[lineup]

ok

1. and if 3 seconds delay is difficult to exactly get,
will 5, 10 seconds do, as well?

2. what is transformer voltage? windings?
1x12VAC or 2x12VAC ?


Regards
lineup delay circuit designer

[kubeek]

Nordic and Rolf: those circuits dont match my needs, I want to have a latch, and the second one I can´t open.

lineup:
the supply will be 1x12Vac, and the delay can be any resonable time.

[lineup]

Originally posted by kubeek
Nordic and Rolf: those circuits dont match my needs, I want to have a latch, and the second one I can´t open.

lineup:
the supply will be 1x12Vac, and the delay can be any resonable time.

I get it, that you have a good quality relay
between the Output and Loudspeaker.

If so
One easy and very smart solution is this:

Get a 2-pole, 2-way relay
(we should use good quality relay, for not too high currents = low contact resistance)

When power on is sensed, a delay circuit is starting to load an electrolytic cap fed by a suitable resistor.
This by resistor current limited source, makes the cap take some time
to reach a certain voltage, at which a transistor starts to conduct (gets 0.7V across B-E)
and turns on relay for loudspeaker output.
pole #1 is for connect-disconnect speaker.

pole #2 is for discharge of the electrolytic cap
so when power is turned OFF,
this pole of relay will close a switch that discharge cap (via a suitable bleeder resistor, of course!)
... and this way the DELAY electrolytic cap is set to zero volt again.

So at power on, this will happen:
'cap', refers here to the electrolytic cap, that sets the delay time

1. The bleeder resistor discharger, is switched off, allowing for cap to load.
2. When voltage reach a certain level in cap, after 3-10 seconds like
- Loudspeaker is connected.
3. Power OFF, and 2 things will happen:
- Loudspeaker disconnected.
- Cap discharge resistor is connected.
4. Amplifier will be ready to be switch ON again, and delay will start from zero time.

I have seen such circuits.
For me or any other clever who wants to design such
it is not too difficult.

Now we know kubeek is using one single winding 12 VAC
for supply, we need almost no other information.
I might even be able to setup such a delay circuit
in my MultiSim to make sure it is working.


PS.
2-pole, 2-way relays are very useful.
The other pole can, for example, Turn on some indicator, LED
or do some other things , that could be needed at Power On.

For example, if one pre amplifier is SWITCHED ON,
the other pole will trigger a circuit that activates Mains Voltage to Power Amplifier!
And when pre amplifier is Switched OFF, the power amp is also SWITCHED OFF.

There are 3 types of these relays:
At no power:
type1- both relay poles are open, and closed at power on
type2- both relay poles are closed, and opened at power on
type3- one pole open and one pole closed
(type1 and type2 are the most common).
DS


Regards
lineup

[Nordic]

K, I don't see, why the realy board would not work for what you want... what exactly do you think prevents this?

To use it to switch something off insted of on, you only need to change it so you use the 2 legs on the relay that are not connected now... the other 2 legs are "switch on side"

Also it runs fine off one rail... as long as you have between 5V and 16V to drive the timer chip... (lower voltage than 12V as per my example would require 6V relay)

[kubeek]

Nordic, as I said in previous post, I cannot open the files in relayboard.zip, so I just don´t know what the circuit is.

lineup: thanks for the relay idea, I just needed the kick in the right way, I was thinking about discharging the cap with some jfet, but this is much better and simpler!

But as I think about it, I need two switches for stereo amp, so I will probably use dpdt relay for output and one small DIP relay for discharging the cap.

[Nordic]

SOrry, misunderstanding there.. you need the free version of Eagle to open those files

[Nordic]

In eagle you need to click ratsnest to fill in the groundplane...

I made this PCB with a blackmarker by printing a mirror image from eagle. tapeing it to pcb, drilling the holes through the picture, remove paper and play connect the dots with the black marker...