Preamp Switch activated by 12V trigger - Page 2 - diyAudio
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Old 25th June 2013, 10:47 AM   #11
DUG is offline DUG  Canada
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Quote:
Originally Posted by DrizztDo View Post
Thank you, the website seems great

...

You're right, I need to know now if the trigger is enough to power the relay. What would be the right way ? Mesure how many AMpere it delivers ?
If the trigger cannot drive a relay, I'm not sure I'll keep on this project.
Use a separate supply for the power for the relays...plug-in transformer.
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Old 25th June 2013, 11:06 AM   #12
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You cannot measure it. It has to be specified. If not, construct a circuit using a transistor as a switch and drive the base with the 12VDC.
DC supply for driving the relay has to be provided using a wall wart or a small power supply.

Gajanan Phadte

Last edited by gmphadte; 25th June 2013 at 11:08 AM. Reason: added content
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Old 26th June 2013, 01:26 PM   #13
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It would such a pity to have to plug a dedicated power source for the switch, when my amp already provides 12VDC.

I couldn't find anything on the trigger out in my amp documentation, except that is is 12V (and that I've found on the net).

I've ordered the assembled relay on ebay. I'll plug my relay to VCC. At least I shoud be able to see if the trigger is enough to switch the relay...
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Old 26th June 2013, 04:23 PM   #14
AndrewT is online now AndrewT  Scotland
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connect the trigger output via 100k load back to the trigger circuit ground.
Read off the voltage across the 100k.
Now swap the 100k to 10k and read voltage again.
Is the 10k Vdrop >= 90% of the 100k Vdrop?
If yes, then swap the 10k down to 1k.
Measure the Vdrop again.
Is the 1k Vdrop >= 80% of the 100k Vdrop?

Swap the 1k to 330r.
Measure the voltage again.
Is the 330r Vdrop >= 80% of the 100k Vdrop?
If yes, you are safe to drive a relay of >330r coil resistance.
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Old 26th June 2013, 04:36 PM   #15
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Thank you I'll do that !
Now I've got some resistors to order
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Old 26th June 2013, 04:49 PM   #16
AndrewT is online now AndrewT  Scotland
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What stock have you got on the shelf?
You only need one for each approximate value.
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Old 26th June 2013, 06:32 PM   #17
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Quote:
Originally Posted by AndrewT View Post
What stock have you got on the shelf?
You only need one for each approximate value.
Let's say I have no shelf...
I've got to look, I have some parts from another project, but don't know exactly what I have in store.
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