Lost in the relays...

[Oddvar]

Hi.  I am building a Dumble OD from layout #183.  Relays are new to me, and since the build and some of the layouts are different, I wonder where the 12v actually go into them, since the relay boards differ a bit differnt. One shows both negative and positive, but the other shows only one?

[tubenit]

I don't know the answer to your question.  There may or may not be an answer to this in the lengthy ARCHIVES thread on relays which has some good schematic, layout and photo information. However, it may not be specific enough for your question.

http://el34world.com/Forum/index.php?topic=14348.0

I am wondering if the top photo simply has a wire underneath the relays (not shown) going to ground also?

With respect, Tubenit

[Oddvar]

One answer could be:

"Positive power is shared between all relays in the amp.  Then the other side of the diode is what is switched to ground (either by toggle or footswitch) to activate the relay switching."

But why is one different from the other?

[shooter]

I'm gonna guess a drawing error since to engage a relay you need both b+ and ground, either can be the "switch" for relay on/off.  virtually all DC relays with have a blocking diode in parallel with the relay coil, the cathode is where you apply +, anode - . 

[Oddvar]

This shows +/- going in.

https://el34world.com/projects/relay_switch.htm

[shooter]

yup, as it should be, and in the example, - is used for switching on/off.

[sluckey]

DC+ goes to the cathode of the diode. If you have three relays, string the +DC to the cathode of the diode on all three relay boards.

DC- goes to a switch and the other side of the switch goes to the anode of the diode. If you have three switches that all operate from a single switch, then string the other side of the switch to the anode of all three relay boards.

But if all three relays operate from three different switches, connect DC- to one side of all three switches and connect the other side of each switch to the anode of the diode on the appropriate board.

[Oddvar]

Only two relays.