Dear experts,
I am looking for solutions to digitally control the route of the pin1 of XLR/TRS combo inputs to either earth or signal ground or lift. PCB mounted miniature electromechanical relays such as Omron G6 are a solution. But are there valid alternative -cost and area effective- solutions?
Thinking of mosfet-transistors, mosfet-based analog switches such as CD4066 or newer equivalent components or optocouplers, I am actually not sure of the electrical requirements related to the pin1 to earth in line-level connections to be effective as earth to earth shield: maximum Ron, maximum current/voltage, earth noise isolation to control signal/gnd/vcc paths, etc
Would you suggest reference components to do that function?
I am looking for solutions to digitally control the route of the pin1 of XLR/TRS combo inputs to either earth or signal ground or lift. PCB mounted miniature electromechanical relays such as Omron G6 are a solution. But are there valid alternative -cost and area effective- solutions?
Thinking of mosfet-transistors, mosfet-based analog switches such as CD4066 or newer equivalent components or optocouplers, I am actually not sure of the electrical requirements related to the pin1 to earth in line-level connections to be effective as earth to earth shield: maximum Ron, maximum current/voltage, earth noise isolation to control signal/gnd/vcc paths, etc
Would you suggest reference components to do that function?
I wish it was that simple! 
Sometimes ground lift may be necessary to fix hum issues.
Also depending on the design of the balanced (or unbalanced) driver, output pin 1 of XLR (or Sleeve of TRS or TS Jack) can be either connected to the chassis or to the signal ground of the driver. That's a common issue in recording studios.
Most of the professional DI boxes and several gears with balanced input provide a mechanical switch to lift pin 1 (called ground-lift, which is actually often an earth-lift). Some high-end professional manufacturers provide a digital control of the ground lift through electromechanical relays.
Since electromechanical relays (+ driver) take some space on a PCB and since they are slightly expensive, I am looking for other solutions than electromechanical relays which can be successfully used to lift the earth/ground pin, without bleeding any audible noise from the earth in the rest of the circuit and matching the electrical requirements of the earth/ground pin of line-level balanced connections.
Sometimes ground lift may be necessary to fix hum issues.
Also depending on the design of the balanced (or unbalanced) driver, output pin 1 of XLR (or Sleeve of TRS or TS Jack) can be either connected to the chassis or to the signal ground of the driver. That's a common issue in recording studios.
Most of the professional DI boxes and several gears with balanced input provide a mechanical switch to lift pin 1 (called ground-lift, which is actually often an earth-lift). Some high-end professional manufacturers provide a digital control of the ground lift through electromechanical relays.
Since electromechanical relays (+ driver) take some space on a PCB and since they are slightly expensive, I am looking for other solutions than electromechanical relays which can be successfully used to lift the earth/ground pin, without bleeding any audible noise from the earth in the rest of the circuit and matching the electrical requirements of the earth/ground pin of line-level balanced connections.
A very good review of the interconnection cases is explained here:
RANE Commercial - Knowledge Base
RANE Commercial - Knowledge Base
In the entertainment industry I can see a use for "lifting " the safety earth including several R/R stars that got a bigger "lift " when clutching a microphone --all the way to the stars.
Anyway in relation to a audio hi-fi power amplifier "lifting " the earth to stop earth loops is helped by adding a 10 ohm resistor between the input signal earth and the heavy -noise containing ,as well as distortion output earth return.
You want to save space ?
Your combination isn't too reliable in engineering terms according to some who use microphones and other inputs I hope you spent your money on a quality combo not some "looking nice " non industrial flashy item ?
Anyway in relation to a audio hi-fi power amplifier "lifting " the earth to stop earth loops is helped by adding a 10 ohm resistor between the input signal earth and the heavy -noise containing ,as well as distortion output earth return.
You want to save space ?
Your combination isn't too reliable in engineering terms according to some who use microphones and other inputs I hope you spent your money on a quality combo not some "looking nice " non industrial flashy item ?
Amp ground lifts still have a path for fault current. And they don't lift the xlr grounds they lift the power 3rd pin. Not the same as disconecting and making it dangerous. Is this not a home system? If your interconnects are humming then a ground disconnect at one end might help. Usually have to lift all ( or all but one ) of the xlr grounds between 2 pieces of gear. But I cant see why you need to do this remotely. Fix it once and leave it.
Another useful resource : https://www.diyclassd.com/img/upload/doc/an_wp/AN_Legacy_pin_1_problems.pdf
When not lifting ground you probably want a good low-resistance ground connection to allow capacitively coupled currents to drain away without generating an IR voltage, so CMOS analog switches are not a good choice (I don't think there are many that can handle +/-18V of professional equipment anyway).
Signal relays with gold-plated contacts would be my choice. (Single MOSFETs are not AC switches and act as diodes when off). Relay/switch contacts that are not gold-plated often need a minimum current flow to self-clean (arc through oxide build-up), so are not suitable for low current signals - over time they become unreliable.
If you want low power you can choose latching relays, although these are more expensive and complex to drive, they don't generate any heat in normal use which can help with thermal management. The power supply requirements for a large bunch of latching relays is much less if you arrange not to switch them simultaneously too.
Signal relays with gold-plated contacts would be my choice. (Single MOSFETs are not AC switches and act as diodes when off). Relay/switch contacts that are not gold-plated often need a minimum current flow to self-clean (arc through oxide build-up), so are not suitable for low current signals - over time they become unreliable.
If you want low power you can choose latching relays, although these are more expensive and complex to drive, they don't generate any heat in normal use which can help with thermal management. The power supply requirements for a large bunch of latching relays is much less if you arrange not to switch them simultaneously too.
Very good AN. Thank you. To the last point of the AN, this is also the route I use when connecting an unbalanced driver to a differential input amplifier.
Regarding the connection of balanced and unbalanced inputs to a differential input amplifier, this is fine if you have two connectors, a balanced one and an unbalanced one. But it becomes tricky when you have a TRS input jack only:
- Pluging a TRS jack with a balanced driver is usually fine, assuming the sleeve is connected to the shield of the driver. Though sometimes it is connected to the signal ground instead of the shield; and sometimes lifting the sleeve is a -bad, indeed- solution to hum issues;
- Pluging a TS jack in a TRS connector likely means that sleeve and ring are tied together. In such case, you might want to route the sleeve input either to the signal ground or leave it disconnected, especially from earth.
That's why many DI boxes and several professional studio gears provide a mechanical switch to lift the pin 1 / sleeve.
I agree. For the time being, latching relays are indeed the only valid option I found. But as you said, they are expensive and they require more or less complex drivers. And they take a significant area on the PCB.
Sometimes manufacturers design ICs to address very specific purposes. Sometimes a smart design can address a similar function by alternative means which fits enough the electrical requirements. But I did not find any convincing solution to make a digitally controlled earth-lift (with optional switch of pin1/sleeve to either signal gnd or earth) yet. So my question in case there actually exists a valid alternative.
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