A question for the electrically inclined

  • Thread starter Thread starter Adam P
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Adam P

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Attached is a picture of the inside of my console, an Allen & Heath System8 (I'm linking it because its a rather large picture).

Just below the first potentiometer, to the left of the rainbow-colored cable, you see two switches: grey boxes with light blue buttons on them that go to the face of the console (you see a similar switch right above; this is the phantom power switch). These two switches engage the talkback circuit; one goes to the cue mix, and the other is the slate. On the underside of each switch are two rows of metal terminals that extend about a quarter inch of the grey housing. These aren't attached to anything. My question is: are these terminals there for controlling a relay in the switch from an external button? Or do they serve another function? Or is it impossible to tell without experimenting?

The reason I'm asking is because I want to be able to control my talkback to cue function from an external switch. The switch on the console is small and hidden behind a volume pot, and my talkback mic has a built in momentary button with leads for doing just that (the mic is a Shure 550L paging mic). If these terminals are for controlling relays then I believe it would be as simple as connecting the mic's switch leads to the switch's terminals. I could test this by simply attaching a piece of wire to two of the terminals and touching the wires together, but I am inexperienced with this and am afraid of doing irrevocable damage.

Any thoughts as to whether or not I'm on the right path? If need be, I will open the console back up and try to find out any part or model numbers, but the console is about 20 years old and the parts are probably scarce.

The link is http://www.opaquedigital.com/bin/mixerinside.JPG

Thanks in advance!
 
The terminals look like through type, meaning the other side is soldered to the circuit board.

You could use the terminals as a switch if they are isolated from the rest of the circuit. You would have to use a digital multimeter to trace the circuit and to verify if all the terminals are actually being used and you would need to check if it is a NO or NC type switch. The switches probably have both contacts. NO = normally open circuit and NC = normally closed.

With all that being said you would really need to know what you are doing to trace the circuits and figure out if what you want to do is possible with your existing circuit.

If you don’t have an electrical back ground or any experience in this I would not advise you do it.


Good luck.


Pier
 
Hey, thanks a lot for your help. A few questions:

Would the multiple pairs of terminals generally be used so that the switch could operate more than one circuit at once?

What do you mean when you say "isolated from the rest of the circuit" ? This switch does one thing: it sends the signal from the talkback microphone to the cue mix. Looking at the block diagram for the mixer (found here), it appears that the signal path is: Talkback mic input > talkback level pot > TB to cue and TB to slate switches. Would this indicate that its isolated or not? Also, because the TB is only engaged when the button is pressed, would this be a normally open circuit?

How difficult would it be to have someone who knows what he's doing figure out whether or not it is isolated? What do you look for when checking with the multimeter? I'm not going to try this, but I do have some friends that are skilled in EE that could probably help me out.

Thanks again!
 
If I under stand you correctly, you want to be able to activate this switch from another area?

If this is so, then yes you can bridge or parrellel the connection and switch it from another location.

you need to analyze the circuit with a multi meter to determin what contacts of the switch to connect to.

I don't know if that helps or not?


Pier
 
Pier Calacino said:
If I under stand you correctly, you want to be able to activate this switch from another area?

If this is so, then yes you can bridge or parrellel the connection and switch it from another location.

you need to analyze the circuit with a multi meter to determin what contacts of the switch to connect to.

I don't know if that helps or not?


Pier
Click to expand...

Yep, thats right. Am I just connecting the multimeter to the terminals on the switch to check? If so, what am I looking for on the multimeter? Just the pair that passes a signal, or something more? Thanks!
 
If that were my mixer I would be afraid that running wires external to it and back to reroute the signal path would introduce a lot of noise. Each length of wire would basically act as an antenna for elecrical noise in the high impedance internal cicuitry, potentially being very troublesome.

That said, again if it were me and I had no recourse but to convert the box to external control I would wire a relay in place of the switch, and have the internal switch in paralell with the external switch connection, so that if either switch grounded the relay control voltage it would switch the circuit. That way, the internal signal path would never leave the box.

Unfortunately, counting pins it looks like the internal switch is an 8 pole double throw, which might be a difficult relay to find, if it actually uses all those switches, which I can't tell from here. It would take some signal tracing with the schematic to find out what all that switch is actually doing.

If you could get one of your EE friends interested, it shouldn't be too much trouble.
 
Hey, thanks.

What I was talking about was not rerouting the signal path but using the wires to control a relay. I didn't know if the terminals on the switch could control a relay in the switch, or if I'd have to add in something like that on my own. I don't want to remove the existing switch, because I'd like to keep the mixer as intact as possible. Again, what would I be looking for in tracing the circuit?

I've put an email in to A&H's US tech support guy, so I'm hoping he might help shed some light as well.

Thanks again for your help!
 
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