I needed a power sequencer for my living room system, and as usual with these things, I saw no need to look any further than Rod Elliot’s wonderful website. Up to his regular standard, the article is well written and considered.
So what is a power sequencer? Why do you need one? Well it is simply a device that turns a series of power sockets on in a certain order and off in another – generally the reverse order. Any loudspeaker system should always be turned on in an order following the signal flow, in my case this is:
1). Turntable 1
2). Turntable 2
3). DJ Mixer
4). Left Amplifier
5). Right Amplifier
I added sixth output in case my system grows.
In addition to this, larger systems may trip circuit breakers due to inrush current if everything is turned on and off too quickly. This isn’t a problem I have experienced at home though.
PCB came together fairly easily, though I made some small changes to the original schematics posted. I added separate LED driver transistors for the indication, since I didn’t want to spare any available current in the BC550 transistors I used to engage the relays. I’m using some large units with a low coil resistance and needed all of the 100mA the BC550 transistors can provide to power them. I use BC550C/BC560C for everything since I picked up a large bag of them a few years ago.
There are a few small issues with my board layout like pin holes for the switch being too small but overall it came together very quickly. As with all things related to mains power wiring, be very damned careful and don’t kill anyone. My build isn’t as neat and tidy as it should have been, and all the photos were taken before I tediously covered up all exposed 240V points.
Other than the power supply for the DJ mixer everything is powered via IEC power cable, so I picked up 6 female IEC sockets for the power output. These fit nicely in a 1U rack enclosure, but drilling and filing the cutouts was a major chore. As with most worthwhile projects I paid for the metalwork with my blood.
I picked the enclosure at the local surplus store along with six Takamisawa (Fujitsu) 18V relays capable of handling 250V at 30A, the kind of overkill I enjoy. Power is regulated using a LM7815. Total current draw with all 6 relays engaged is ~500mA. The 18V relays engage at 12V so the 15V rail is no issue and even reduces the overall current draw. Maybe if it was inside a washing machine (the intended environment for the relays) they would need the extra staying power but in this case it works fine. These relays had the benefit of having ‘Faston’ style connectors for the switch circuit and smaller tabs for the coil on the other side of the device.
I used a piece of aluminium L bracket drilled and mounted to separate the 240V section from the relay triggering. The sheet steel enclosure is would flex a little so this had the handy side effect of stopping that from happening as much. It also meant that I could separate the 240V and coil sides of the relay.
Anyway, all done. Works. Easy to use.