GND Scheme questions

[Newmarket]

Yes, I undertand this. The confusion is that the pin 1 of the Dim D is not wiring to shell.

Dimension D, and pin 1 of the XLRs are all connected to signal ground, whilst the XLR shells are connected directly to chassis ground. Roland perhaps expected the use of cables where pin 1 is not connected to the shell.

And I don't know if is secure to tie signal ground, and earth ground in this 30 years device.

So, I think that I will wire like the original.

Pin 1 to signal gnd. And XLR shells to chassis.

tbh it seems rather pointless and time wasting to ask on here then ignore all the good advice.

 

[spoontex]

tbh it seems rather pointless and time wasting to ask on here then ignore all the good advice.

I am reading the documents that you have posted here. To undestand and do it properly. Avoid that post. I don't want to wire like the original. And obviously, I am grateful for the advice received!

 

[spoontex]

It seems this is the most obvious way to wiring. Changing TS jacks with TRS. But doing this, they short the ring to gnd and I think this is not a good idea with a power transistors output stage. This way short one phase of the output to gnd.

 

[sahib]

.....Changing TS jacks with TRS.....

Why?

 

[spoontex]

Why?

yes, you are right... it's the same.



I don't know how to mess with balanced, unbalanced and ground.

 

[ccaudle]

Changing [output] TS jacks with TRS. But doing this, they short the ring to gnd

Correct, using TRS jack is only recommended if you have either impedance balanced output (where the cold connection to ring is the same impedance as the hot leg, but not driven by an op-amp), or one of the cross-coupled circuit designs which is intended to mimic the behavior of a transformer, such as THAT 1606 or 1646 output driver, or a real transformer.
A user would also be expected to know to never use the unbalanced and balanced outputs at the same time, since that would put a double load on the balanced output hot leg, and results in unbalancing the connection. It will still pass audio, but may introduce additional noise.

I don't know how to mess with balanced, unbalanced

Do you need to? Simpler to have only balanced. That removes having to deal with multiple types of connectors, and gets rid of that gain switching circuit that changes gain based on whether a phone plug is inserted or not.
Or did you want to use this inline with a keyboard or something that only has unbalanced connections?
I'm sure that is why Roland made the original design with both, they wanted to sell as many as possible so they made it usable with balanced mixers, unbalanced effects send/return connections, connected directly to your Roland synthesizer, etc. but if you are building something you can build exactly what you need and leave out unnecessary complications.

 

[sahib]

If you do not need to isolate the XLR when you are using the jack for unbalanced input/output then simply use a TS jack and tap into one leg only and ignore the other.

But if you want to isolate the XLR then wiring the input is not a problem as you will be grounding one leg of the input.

But for output wire it like this.

When a mono jack is inserted Tip gets the Hi and Ring is connected to the Lo of the XLR. Even if there is a balanced equipment is connected to the (output) XLR, it is still not a problem as one of its (balanced) input will be grounded.

 

[spoontex]

And now only for curiosity. If I use booth type of connections. Balanced and unbalanced. An RF network will help with the unbalanced connection? 100R with 100nF.

 

[FIX]

I was grounded a few times as a child. Once was for being expelled from school for a week after lighting my volcano science project inside the "high" school. An entire wing of the school filled with smoke which resulted in a school wide fire drill. I mean common man, it was done in the name of science! And the fire drill was a success. I took that as a win-win, but the assistant principal didn't see things my way. I was grounded for that week off of school and my old man made me chop a cord of wood with an axe. Memories of grounding!

I help to make the school smell like vomit, but they never figured out who did it...

 

[sahib]

No, not like that. Now the source is seeing a 100R load.

For RF protection use inductor beads in series.

I also recommend proper input/output protection using clamping diodes.

 

[ccaudle]

Balanced and unbalanced. An RF network will help with the unbalanced connection?

You will definitely need an isolating switch like shown, because the load on one input is different than the other.
That can sometimes help if the unbalanced source has a three-wire power cord with protective earth connection, but for a two wire power cord the unbalanced device is floating, so if you do not have a good connection between the unbalanced input of a floating source and the chassis of the balanced receiver the unbalanced source can float on a relatively high level AC common mode.
I had that problem recently, I was connecting a Roland synthesizer to a sound system with a transformer based DI box, and I was getting a really high level buzz. It turned out to be because the DI had gotten switched to ground lift, so there was no connection between the keyboard circuit ground and the stage box ground, so all the high level, high frequency eyboard power noise was getting through the transformer parasitic capacitance. Flipping the switch so there was a hard connection between the keyboard ground and the stage box ground solved the problem.

Do your unbalanced sources have three-wire power connections? If not you will definitely want the phone jack to just have a hard connection to chassis for the sleeve.

 

[spoontex]

The switchcraft 113epcx have isolated switch internaly with nylon. And I need to isolate the phone jack itself from the chassis because the interface switch. If not the unity gain switch will be activate all the time. My idea is isolate this phone jack and tie the sleve direct to the pcb signal ground. Is the only way I know.

 

[spoontex]

Sorry for my insistence. What about this? it's not supposed it's to fit an single-ended connection to grounded device? I will not use both ( xlr, jack ) at the same time.

 

[ccaudle]

ie the sleve direct to the pcb signal ground.

So talk through that. The sleeve is the connector terminal for the cable shield. Complicated slightly for unbalanced connections because it is also signal return, but still unambiguously the cable shield connection.

Cable shields carry power line related currents as well as RF interference currents. You want do connect all the interference currents directly to your circuit reference node?
Describe your thinking there about why you want to connect the shield currents into your audio circuit, or why you think that might be necessary or desirable. Note that this is intentionally designing in the "pin 1 problem" previously described, where interference currents will have to flow across your audio circuitry to complete the current path, as opposed to just flowing across the chassis.

And the converse, what problem do you think will occur if the connection of the shield to your reference voltage is across the chassis, and to the common point which defines the voltage reference point for the equipment?

Is the only way I know.

I thought perhaps the previous four pages of discussion had expanded the ways you know.

What about this? it's not supposed it's to fit an single-ended connection to grounded device?

I don't quite follow the question, but note the description of the picture is what is common on semi-pro gear which has balanced and unbalanced inputs. Earlier in the discussion it notes that "the RC network...can usually be shorted" but the simplified picture leaves out any switch around the R and C combination you would use to do that.
Note that if you use TRS input connector rather than RCA, then connecting a TRS cable from an unbalanced source to the balanced input is the same thing as the RCA-to-XLR adapter cable described in that Hypex document with the direct connection instead of RC connection in place.
Also note that the Hypex document shows that the RC connection, when not shorted, is to the chassis, not directly to the audio circuit reference node.

I understand your wording in your question now, unbalanced connections on devices with or without safety ground.
The considerations are a little different for devices without safety ground, and in some ways easier if every device connected together has no safety ground. That is often the case for consumer equipment, for example all of my commercial home audio equipment has just two conductor power cable. It works fine because all the equipment in a particular system is powered from the same power outlet strip, so there is not much voltage difference which can develop between any two devices.
I'm also going to point back to that presentation by Whitlock again, because that is covered starting on page 60.

 

[spoontex]

And the converse, what problem do you think will occur if the connection of the shield to your reference voltage is across the chassis, and to the common point which defines the voltage reference point for the equipment?

All the interferences that carries the shield would go to the audio circuit.


But I can't use TRS jacks for unbalanced as you suggested.

" What Roland did in the Dimension D is a real balanced output, driving the two wires with opposite polarity - but not like a transformer, i. e. not allowing a short of one end of the output. This is why Roland had separate jacks for balanced and unbalanced outputs."

I will short pin 2 to gnd if I use TRS jacks with mono jack cable.

So, I will mount the TS with isulated washers and direct to GND pad's, instead to use the chassis as conductor.

Most of time I will use XLR, but I would use unbalanced If I need it.

 

[ccaudle]

Seems like everything has settled down here, time go go build!
Let us know how it turns out.

 

[Speedskater]

Wait! let me add my take on the subject:
a] Safety Ground/Protective Earth, bonded to the metal chassis near where the AC cord enters.
b] all cable shields attached to the metal chassis near their connector.
c] analog circuit common and DC supply common attached to the metal chassis near the input connectors.
this may be thru a low Ohm resistor or network.

 

[merlin]

Most of time I will use XLR, but I would use unbalanced If I need it.

Then you should change the driving circuit. Instead of the original transistors, use a DRV135 or similar. It will solve all your problems.

Or use impedance balanced output instead of fully balanced.

 

[spoontex]

Seems like everything has settled down here, time go go build!
Let us know how it turns out.

Yes, build time!!

 

[ccaudle]

Then you should change the driving circuit.

For a new design I would fully agree, but it seems like the original poster is probably building from a kit and does not have experience yet for extensive circuit modifications. Everything in steps.