Modifying audio console

[thisisliam]

Good afternoon!

New to the boards and excited to be here. I've been experimenting with creating my own PCBs lately and am attempting to modify an existing piece of gear. I contacted the manufacturer and they informed me that what I want to do is possible with some diodes, but won't elaborate further. While I'm relatively familiar with how everything is connected I don't want to damage the unit.

The unit itself is a four wire box - four XLR inputs, four XLR outputs, an XLR microphone input, a 1/4" headphone output and four switches that when actuated output the mic signal to that corresponding output. The inputs are monitored via an internal speaker which is cut when headphones are plugged in. The inputs are not routed to the outputs. Each of the four switches has an LED that illuminates when that channel is hot (switch is actuated).

What I'm wanting to do is add a push button that will allow me to "all talk" to all four of the outputs rather than actuating all four switches at once.

As mentioned above, the manufacturer said some diodes will achieve this, but that is all they're willing to tell me.

If anyone interested is open to helping push me in the right direction I can post some photos of the board and unit on here.

Thanks!

[ogden]

What I'm wanting to do is add a push button that will allow me to "all talk" to all four of the outputs rather than actuating all four switches at once.
As mentioned above, the manufacturer said some diodes will achieve this, but that is all they're willing to tell me.

They just don't want to waste too much resources on you, but if they say so then not that much effort is needed. Please tell make and model of console and don't omit this part of information in the future. Could you provide picture of controls, and some pictures of inside boards, especially those which are related to said buttons. In case console is digital one, and buttons does not route analog signals but just logical states/commands for DSP - you need to measure voltage (against ground) on all contacts of the button when it is pressed and when not. Better do it on at least two buttons to see - they work same way or not.

[thisisliam]

They just don't want to waste too much resources on you, but if they say so then not that much effort is needed. Please tell make and model of console and don't omit this part of information in the future. Could you provide picture of controls, and some pictures of inside boards, especially those which are related to said buttons. In case console is digital one, and buttons does not route analog signals but just logical states/commands for DSP - you need to measure voltage (against ground) on all contacts of the button when it is pressed and when not. Better do it on at least two buttons to see - they work same way or not.

Totally understood. I did offer them payment for their time, but I understand.

The unit is analog. I can provide photos once I'm home from work. The unit is the FW4010 by CTP Systems out of the UK.

[ogden]

The unit is analog. I can provide photos once I'm home from work. The unit is the FW4010 by CTP Systems out of the UK.

This one? http://www.ctpsystems.co.uk/fourwire.html Is this kind of announcer system console for shopping malls or what? I noticed promising "key latch enable" option on back which most likely means that audio is not routed through switches and what manufacturer said about diodes, may indeed be true. Now we wait for some photo of internals and your probing results.

[thisisliam]

That's the one. Indeed it has multiple purposes. This one I'm wanting to modify is for use in a control room on a reality TV show. The user can monitor the actors microphones and "speak" to various parts of the set.

[thisisliam]

Ok, I've attached some photos. The little wires look like a spaghetti pile, so please see below for some further info. If you look on the PCB you can see "J" labels where the connections are made to the PCB...

- The toggle switches are wired to J16. Toggle switch #1 uses green and brown wires. Toggle switch #2 uses red and blue wires, etc.
- The DIP switches are wired to J18.
- The XLR outputs are wired to J13.
- The IFB inputs are wired to J6.

If you need me to "map" out the board in more detail please just let me know.

I believe the addition of diodes and another switch need to be connected to J16 in some form. One of the photos shows the back of toggle switch #4 (gray and yellow wires).

Edit: The jpg files appear to be too large for posting on this forum. I've included a link to a wetransfer download link - https://we.tl/t-I1YyS0qwF8

[ogden]

If you need me to "map" out the board in more detail please just let me know.

Pictures are good, your analysis as well.

One of the photos shows the back of toggle switch #4 (gray and yellow wires).

Very important part of info (I missed?) - toggle switches. Only thing remains - trace where middle (bare) wire of all buttons go, where it is connected. I bet it's either positive rail of PIC MCU or GND. Could you check using DMM continuity or diode mode - it is connected to ground or not? If does not trace to ground, then check if it's trace against supply of PIC MCU. You could switch it on and measure voltage on that middle terminal of one switch against ground.

I believe the addition of diodes and another switch need to be connected to J16 in some form.

Yes, most likely you shall look for similar toggle switch and 8 (small signal) diodes. Middle terminal of added switch shall be connected to middle terminals of others. Only question remains - you have to connect anodes to new switch and cathodes to existing or other way. Hopefully your measurements will tell. [disclaimer] Please test your modification first, only then drill hole for new switch

[edit] I would *not* try to connect anything to J16, but solder wires to terminals of existing switches instead.

[edit] This forum engine supports picture attachments, look for "+ Attachments and other options" below edit box. Just make sure before upload to downsize them into sensible dimensions and file size.

[thisisliam]

@ogden - thank you for your help Were you able to see the photos in the download link? I'll try and down-res them so they can be uploaded directly.

The middle contact on all the switches are connected to each other and a wire (black) is run into one of the terminals in J16. I'll try and test to find the answer to your question.

I think I understand what you're saying though. So each existing switch would have a diode soldered to each solder lug and (pending testing) the new switch would daisy-chain accordingly and that would allow the user to "speak" directly to all of the channels? The question I struggled with before I started this project was if a rectifier diode was what I would need.

[thisisliam]

See attached

[ogden]

@ogden - thank you for your help Were you able to see the photos in the download link? I'll try and down-res them so they can be uploaded directly.

Yes, it worked for me. Just took extra effort. It's good that you uploaded images here - for those who are just reading this thread.

The middle contact on all the switches are connected to each other and a wire (black) is run into one of the terminals in J16.

Black sounds to me like ground. You could measure voltage on all three terminals of single switch which is not pressed. It will be enough.

So each existing switch would have a diode soldered to each solder lug and (pending testing)

Yes. If black wire is ground then you solder anode end of the diode to lug with color wire, each switch receives two diodes. I would suggest small generic 0.1A Schottky diodes like BAT42. Big high current rectifier diodes could have big forward voltage which may render microcontroller unhappy with resulting level of the signal received.

the new switch would daisy-chain

Not daisy-chain. New switch receives cathode ends of diodes, four wires from existing switches upper diodes to upper lug and four wires accordingly to lower lug. So when you press new switch down, it pulls all lower wires of existing four switches to ground through diodes which are required because that pulling shall go only one way (diode does exactly that, "one way").

[edit] I have no mood nor time to draw even such a simple schematics. If you need one - try to make it happen and show. Then I can confirm - it's ok or not.

[edit] Forgot to say repeat that middle lug of new switch shall be connected to mid-lugs of other switches.

[thisisliam]

@ogden - no need to draw the schematic. I understand what you're saying. Thank you for your help! 

[ogden]

Any progress?

[thisisliam]

Hey Ogden!

Yes, I've ordered the parts I need. Won't be able to start modifying and testing the unit until after Christmas.

The switches read at 200mA 12VDC with a multimeter (no markings on them), so I ordered bat42 .2a/30v diodes. Thing is - the push button switch I have available for this project is rated 5A 125/250VAC. Another user on the board said I shouldn't have issues with this, so I'm going to test it when I get a chance before ordering more parts.

The centre pole of the existing switches are connected to the microphone, so believe it is the positive rail.

[ogden]

Overrated switch cannot be an issue. Thou I am not sure about your "switches read at 200mA 12VDC" measurement, but whatever. It is not that important anyway. Connect one or two existing switches to new switch and test. If does not work - you shall reverse diodes and test again. That's it - as easy as that.

[thisisliam]

I appreciate your help my friend. I'll post when I've got everything in place!

RE the multimeter test - I tested to see what the current was flowing through those switches when they are and are not actuated. Curious what result you might've been expecting? (learning the lingo here...)

[Kilrah]

You most likely measured current wrong and shorted something, becasue there shouldn't be anything significant, a couple of mA at most but certainly not 200.

[thisisliam]

@Kilrah - 200mA is .2 amps?

[Kilrah]

Correct.

[ogden]

RE the multimeter test - I tested to see what the current was flowing through those switches when they are and are not actuated. Curious what result you might've been expecting? (learning the lingo here...)

Such current measurement is essentially shorted power supply in your case. Device or multimeter may not like it - may blow fuse or make smoke. In future try to not measure currents "out of the blue" in your electronics.