I acquired an old analogue Studer Telephone Hybrid with a built in Dual Relay Card. When I recieve a call, I want to send the output not through my telephone but through the XLR outputs of the unit. So I need to switch the output (and input) in the hybrid itself. For that there is a 15-pin d-sub connector and, from the manual, the following info on how to connect the pins: https://photos.google.com/share/AF1QipMnKU5zqQfsvyuhKgIdgySpBArVNtKNA87xsd3ITXn4nZTT7-T8jYQNCZPm7-tVtA?key=V3RNWThFTDdtcWpvZWZYNFB0WjR3WFZxbTg1bEVn

In case the link becomes unavailable, here's an ASCII transcript. If this is the d-sub connector:

 - o8  o7  o6  o5  o4  o3  o2  o1-
  - o15 o14 o13 o12 o11 o10 o 9 -

then these are the connections:

 ___                        |    ______
| - *___*   o   o   o   o   *   * -
|  - o  |o   o   o   o   *___*   -
|   ----|----------------|-------
|       |                |

So apparently pin 7 and 8 as well as pin 9 and 10 are bridged. Does that mean that the pins are just soldered together? Unfortunately I'm new to electronics, and I can't quite figure out which pin goes where. I have a push-button switch (an EAO 31-261.025 with a lamp in it) which has 6 terminals that look like this:

|o 1   3 o|
|  -   +  |
|o X1 X2 o|
|         |
|o 4   2 o|

and I have soldered on the pins 1 on the d-sub to pin 1 of the switch and then pin 9 and 10 both onto pin 2 of the switch. Turning on the hybrid destroyed the 200mA fuse, so I probably made a mistake. How do I correctly connect the switch to the 15-pin d-sub connector?


Judging from the third picture of the shared album on Google Photos, the switch connected to the d-sub needs to short the pins 7 and 14 (and/or 8 and 15 depending on channel). After opening the hybrid up, I saw that the pins 1 and 2 as well as 14 and 15 had a blob of solder between them, so apparently I don't need to connect these myself!

The wiring diagram in the third picture should look something like this:

     _______diode____[   ]______
    |     __diode____[   ]__    |
  - *,,,*   o   o   o  _o___*   *_-_____*
   - o   o   o   o   o|  *,,,*___-_____*/    <--- switch 1
                      |  |
                      *-.*                   <--- switch 2

where the commas refer to internally bridged pins.
Since I can't figure out this EAO switch I found a generic DPDT slide switch with 6 terminals. Now I have (replaced the fuse and) soldered the terminals like this:

| 7 o  o 8 | <-- pins 7 and 8
|          |
|14 o  o 15| <-- pins 14 and 15 as ground
|          |
|   o  o   | <-- nothing soldered on here

Having tested that, it still wouldn't switch (but at least my hybrid keeps turning on). Did I solder the d-sub pins to the wrong terminals or did I miss out on something? Or may I have destroyed more than the fuse at my last attempt? :(


1 Answer 1


Most telephone hybrid units intended for Broadcast use have an option for "Auto Answer", many also have the option for "Auto Disconnect".

I haven't looked at the Studer Hybrids for decades and don't recall if they have that option.

FWIW - my favorite Hybrids are something like the Getner DH20 or the version of the DH-20 customized for conferencing: AP-10. That said: my last few projects have used Hybrids from Telos.

  • \$\begingroup\$ If my ol' Studer (it's from the early 80s, the circuit diagram points to 1978) explodes from plugging my self-soldered switch in, I'll check these out. :D \$\endgroup\$ Mar 17, 2017 at 20:29
  • \$\begingroup\$ Bear in mind though, since my Studer has a dual relay card, the manual states that my use case should be possible - as long as it's actually functioning as it should. (It still passes through the telephone line to my phone though, so I guess everything's still intact...?) \$\endgroup\$ Mar 17, 2017 at 21:22

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