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Old 24th October 2005, 10:59 PM   #1
Bryan is offline Bryan  United States
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Default Need Advice with Timer Relay Shut Off

Hey Guys,

So, I have an issue I would like help solving.

I am currently running a 12 volt timer relay from my fillament regulator, schematic attached. I am taking the DC to feed the timer from the second filter cap in the regulator, which is working fine, albiet the voltage is a little high. When I power up, I have an approximate 30 second delay before the outputs are un-muted (if that is even a word???).

Now, my problem is this. When I turn off the power to the pre-amp, the delay does not immediately trigger (turn off = mute output). I assume this is due to the large capacitance of my filter caps, stored voltage, and slow discharge time. Now, if this is correct, I am wondering how do I solve the problem.

Any and all input is appreciated.

Thanks,

Bryan
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File Type: gif fillament supply.gif (12.0 KB, 220 views)
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Old 25th October 2005, 03:02 AM   #2
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The basic solution shall be putting another rectifier circuit with smaller
capacitor to supply just to the relay. Good luck!
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Old 25th October 2005, 03:18 AM   #3
paulb is offline paulb  Canada
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Yup. A diode and smaller filter cap connected directly to the AC input.
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Old 25th October 2005, 02:10 PM   #4
Bryan is offline Bryan  United States
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OK,

So it seems a seperate rectifier will be necessary...

With respect to this rectifier, and the suggestion of a diode and small cap...

From one leg of the AC or both, and bridge or not. For the cap, what size, maybe 100uF at the appropriate voltage? Could I simply attach a diode to one leg of the AC, filter it on a cap pulling the positive DC from the positive arm of the cap and taking the ground from the negative lead of the cap? Would I need to refference true ground in this set-up?

Thanks,

Bryan
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Old 25th October 2005, 04:21 PM   #5
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Hi Bryan,

There are two parts to a solution for your problem.

First is to drop the relay immediately on power off. This can be done by using a DPST power switch. Use one pole for the AC power in the normal way and put the coil of the delay relay through the other pole.

If that is all you want, you are done. However, if you want to make sure that the relay will not pick if the power is immediately turned back on before the power supply has had a chance to bleed down you will need a more elaborate solution.

For this, you might consider some sort of 555 timer circuit - do an Internet search there are many out there. This will need a separate power supply like already mentioned. A single diode and small capacitor referenced to ground would be okay here. The size of the capacitor will depend upon the current draw of the relay, so choose it empirically. 100uF would be a good place to start.

Dave
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Old 25th October 2005, 04:35 PM   #6
Bryan is offline Bryan  United States
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Thanks Dave,

As the amp is currently, there is a 555 based timer circuit which can either open or close the relay (depending on configuration) after a set amount of time. So, at power on, the circuit begins to count out 30 seconds at which point it triggers the relay to OPEN, thus deactivating the outputs short to ground and thus un-muting the amp. At power off, the relay immediately returns to the original configuration, which will mute the outputs. The issue is that the power is slow to bleed, and this the trigger is not instantaneous with power off. I am going to try the diode and cap to see if this helps. It currently takes about 3-4 seconds after powering off before the voltage drops enough to reset the relay. This wouldn't be a problem, but the HV drops faster than that, and thus the output of the preamp jumps all over the place resulting in pops and bangs.... NOT a good thing!

I'll try to post the link to the relay I am using in a little bit...

Thanks,

Bryan
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Old 25th October 2005, 04:53 PM   #7
Bryan is offline Bryan  United States
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Here is the link to the delay kit I use.

555 Delay Timer
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Old 25th October 2005, 07:43 PM   #8
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Hi Bryan,

It looks like you have the second part covered. There is a 470uF capacitor on the timer circuit so you might need just the diode. It should be simple enough to wire it up and try.

If that doesn't work for you, try the power switch, I know that will work.

Dave
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