Power-delay timer for 5/12V triggers
January 27, 2019 2 Comments
This small design is actually a solution to a problem I have, but as it’s also one I’ve seen others describe from time to time I still find it worth sharing.
My current preamp is discrete and has a 15-second delay before the output is turned on (to allow it to stabilise). This means that the poweramps I use will turn on before the preamp and consequently I get a bit of a turn-on thump in the speakers when the preamp turns on. There is a 12V trigger output on the preamp, but even if there was a trigger input on the poweramps as well (and there isn’t) the 12V trigger is active immediately and so that doesn’t really help.
Of course you can solve this manually by waiting for the preamp to switch on fully, but 15 seconds feels like a long time when you’re just waiting and so I decided to do something to address this terrible hardship… 😉
The easiest way to fix it – introduce a longer delay before turning on the power amps – only required a modification of my previous delay circuit to power a bigger relay, so that’s what I did. The relay I’ve chosen is an Omron G5LE which is rated app. 5A with a reactive load, so that should be fine for most amps in the power range that I normally use. Not all manufacturers publish the specs of their 12V triggers, but those that do generally state a max. current capability of 100-150mA. As a single 12V board draws app. 45mA with the relay engaged powering one board should be fine and even adding a second should be trouble-free as well.
When I made the board I only really could see the point of a 12V version, but afterwards I realized that a 5V version would be able to work with USB-power and that might be worthwhile as well. On 5V the current consumption should be just under 100mA, which pretty much any (non-portable) USB source should be able to provide.
I’ve tested the circuit and it works as expected, so apart from still being on the lookout for suitable case it’s more or less “mission accomplished” for this one 🙂