Questions about relay boards to convert 12V triggers to contact-closure

[jhaider]

I recently discovered that turning on the "auto standby" setting in Audio Architect on my Crown subwoofer amp only turns off the high power rails, and true standby (<1W consumption) is only possible via engaging the contact closure through the AUX connector. So I want to do that.

Looking around amazon I see a few options that mention 12V triggers and contact closures. I have questions.

First, do I need one per amp or (assuming no disparate delay is required) can one work on two amps? (Reason for asking - still vacillating between adding a Crown DCIn amp to power 7-series monitors, vs. BSS BLU-50 and my existing ATI AT4007. I need to do a hiss test to see if the Crown solution is quieter than the BSS+ATI solution. Also, my AVP manual lists 50mA trigger current, but is ambiguous if that's total or per trigger output. I have a question in to them regarding that ambiguity.)

Second, a quick scan of Amazon turned up a couple inexpensive boards that seem suitable for purpose.

• ELK912 and ELK912B "Heavy Dute" [sic] - more expensive than the below but reassuring because the company has a website with technical data sheets, they're also offered by industry suppliers such as Newark. An Amazon review of the B-model states "This little board has all the parts needed to take the 12vdc trigger output from a receiver or preamp and drive a dry-contact-closure detection circuit..." The base model has no such reviews, but the differences between these two seem to be an LED, input style (ELK912B is fussier when dealing with small wires such as inside cut-off headphone cords), 5mA of current draw (30mA for base model, 35mA for B model), and 4 bucks. So I see little reason to get the B-model. Am I missing anything?
• HiLetgo 12V 1 Channel Relay Module With Optocoupler Isolation Support High or Low Level Trigger - this one has fancy lights (do not care) yet is less than half the price of the ELK912B, and a user review could not be more on point: "Perfect for controlling a Crown amp via 12VDC trigger." However, an Amazon review states the current draw is actually 43mA, not the claimed 5mA.

I'm sure there are others, but this is enough analysis paralysis already! Between those three, my inclination is ELK912 - lowest power draw, more convenient terminals (IMO) than ELK912B, marketed by a company with a US office in case it causes damage.

Third, assuming it will not be in a visible place, is a case of some sort necessary? Or can the board just be stuck out of the way somewhere (e.g. double-stick tape to a shelf in a rack cabinet?

 

[somebodyelse]

I don't think you're missing anything with the ELK912 - I don't see a reason for you to get the heavy duty one either. It's about as basic as you get - a relay, a freewheeling diode and some screw terminals. The down side is if you need two but the AVP turns out to be limited to 50mA total.

The HiLetgo is a more complicated and versatile beast which is probably the reason for the confusion about the current requirement. It has an opto-isolated input that only needs a small current (the 5mA) and can be driven from a low voltage - ideal for something like a Raspberry Pi. The relay coil is on the other side of the isolation, so it has a separate 12V supply input for this, which needs to supply the current the relay needs to switch - the 43mA. Also since the opto input is an LED and a series resistor chosen to give enough current to operate at 3.3V, when you feed it with 12V it will draw more current. You can add a series resistor to drop the current if you need to reduce the current.

For two amps I'd be looking for a double pole relay module, or one with two relays, as that way there's no need to look into how the amp implements its dry contact sensing and whether you could get away with a single contact.

Since it's all low voltage and low current it should be safe just tucked out of the way, but I'd probably box it anyway to protect it from stray conductive things once it's been forgotten about.