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PostPosted: 13 Nov 2012, 13:24 
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Joined: 01 Nov 2012, 01:33
Posts: 1
Location: Oklahoma City
After disconnecting 125vac, would the power supply capacitors in the diagram below provide enough dc current to power the amp for a second? If so, why couldn't we just kill the headphones with a switched relay? To keep it simple for the user can I use a dpdt switch to control both mains voltage and 12vdc? would this work for a power off solution?


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PostPosted: 17 Nov 2012, 23:33 
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Joined: 18 Jul 2012, 17:45
Posts: 3
johnbokc wrote:
After disconnecting 125vac, would the power supply capacitors in the diagram below provide enough dc current to power the amp for a second? If so, why couldn't we just kill the headphones with a switched relay? To keep it simple for the user can I use a dpdt switch to control both mains voltage and 12vdc? would this work for a power off solution?


I do not recomend put the 125vac on switch with the amp for security reasons (you can use a separate switch for this). The off delay work like a "standby" circuit, it must be energized to function.
If you are using the delay I posted, use this way:
Image
Hand draw sorry the quality... :blush:


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PostPosted: 08 Feb 2013, 15:42 
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Joined: 08 Feb 2013, 15:20
Posts: 2
Hi, first post here, stumbled upon this thread with Google. I have a good solution for this...

This circuit is a bit old by now and if I find some time I shall edit it a little with mosfets instead the NPN transistors. Also it was designed for a specific amplifier that turns on by connecting one status pin (MUTE+SLEEP) to ground. The same point can be used to ground a relay that turns any amplifier on. The point is that it always first turns the amplifier on, then the speakers and vice versa. Nice feature is that the speaker relay transistor can also be pulled down by a protection trigger circuit, to ensure the speakers will also be disconnected if the amplifier senses a problem.

Image

Here you can see it functioning with two leds, this was built on a breadboard to test just after I designed the circuit:



I found this website when I was looking at various delay circuits. Most delay circuits don't reset properly, or not at all. You can also make one that properly does that without the need of a 555 timer. Here's another circuit I more recently designed:

Image



The latter circuit only provides turn on delay, while the first one does a 1-2,2-1 sequence. Both can be very interesting for audio, even a little time delay on can prevent the fuses from blowing when all equipment is turned on at once.


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PostPosted: 08 Feb 2013, 16:57 
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Joined: 08 Feb 2013, 15:20
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Redrawn the top circuit a bit to make it more general to be used with any amplifier:

Image


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PostPosted: 08 Feb 2013, 18:14 
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Joined: 04 Jun 2008, 20:59
Posts: 3510
Location: Arizona, USA
Hi, This may have been covered already...but why not use a type 555 IC to do the chores. A dual one could allow for different delay on and delay off times. Nice thing is they are source voltage independent within their ratings so fluctuations in the supply voltage to them won't upset the time delays.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


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PostPosted: 02 May 2013, 03:42 
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Joined: 02 May 2013, 03:27
Posts: 1
I am building a power amp a Naim Nap140 clone. This has the output protection stripped off to improve sound quality. Also I want to stop switch on/off thump. After much research I decided that the protection chip C1237HA offers the neatest solution. This operates a relay after a delay and also senses output for DC and then will disconnect. Usually this is used to connect the speakers via a relay. This protects the speaker from dc, but offers no protection to the amplifier.
I am wondering whether configuring this to delay the connection of the power supply to the amplifier might be a better solution. As the chip provides a 'latch' option there is no danger of the amp being turned on/off continually in the event of a fault. Using it like this would protect the amp and the speakers.
I am wondering if anyone has tried this. Also can anyone provided an explanation as to why this approach rather than using a relay to switch the speakers in/out is not more widely practiced.


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PostPosted: 02 Dec 2013, 18:28 
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Joined: 31 Dec 2008, 15:34
Posts: 441
Location: Denmark
Thanks to all for your interests and inputs !

My solution has for a long time been two contacts, to solve the problem. One to on/off power and another to on/off the headphones. Turning on power go from left to right contact and turning off, go from right to left contact ....very simple.


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PostPosted: 06 Apr 2017, 09:39 
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Joined: 13 May 2016, 02:02
Posts: 62
Location: Javea, Spain
Hi Kramme,
All photos have disappeared from this thread. Any chance you could put them up again as I would like to add this delay circuit into future amp builds.


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