500 series design questions

[JMan]

I'm working on a layout for a 500 series pcb, and I have some questions about the grounding scheme used in 500 modules.

I see that there are three pins on the edge connector that are used as "grounds" (I understand that this is probably not the most accurate term to apply to all three, but I'm going to use it generically here).

Pin 1 - "Chassis"
Pin 5 - Audio Common
Pin 13 - Power Supply 0v

The connections seem fairly simple. Power rail grounds connect to pin 13, audio grounds to pin 5, and mechanical things like the L bracket (?) to Pin 1. Does this seem right?

If that makes sense, then I am wondering where the best place to connect something like a transformer shield would be. My instinct says Pin 1, but I'm unsure if I'm grasping these connections correctly.

EDIT: I've updated the title of this thread, as there are more than just questions about ground schemes that have come up for me in the discussion.

 

[Bobby Baird]

Sounds good JMan. Here's an excerpt from Radial Workhorse Datasheet.

Grounding
Following the AES Specification, Pin-1 connections of the Workhorse rear panel XLR connectors are permanently
connected to chassis ground. The ground of these cannot be lifted. The chassis ground is then connected to
pin-1 of the card edge connector to allow for a direct chassis ground to any XLR or other balanced connectors a
manufacturer may see fi t. A ground lift switch may be added to the module at the manufacturer’s discretion.
The modules themselves have two separate ground paths: an analog ground on Pin-5 and a power ground on Pin-
13. These are routed separately through the backplane and are joined at the power input connector. The analog
ground must only be used for grounding actual audio signal. The power ground could be used for anything where a
ground is needed that does not carry audio. They should not be tied together within a module.
The power load for each module should be balanced as much a possible between the positive and negative supplies.
Especially loads that switch on and off such as LEDs and relays. Operating these loads from rail to rail (not through
ground) will result in less ground induced noise.

 

[JMan]

The power load for each module should be balanced as much a possible between the positive and negative supplies.
Especially loads that switch on and off such as LEDs and relays. Operating these loads from rail to rail (not through
ground) will result in less ground induced noise.

Thanks so much Bobby, this is very helpful! Regarding the portion quoted above, I am fairly obtuse about how to do this. I do have one relay that will be included (all other active components use the dual rail supply), and I was just planning on running it between +16 and power supply common. How would I go about balancing that between the rails instead? (Or rather, if that’s annoying to answer, do you know of any resources that I could seek out that explain it in simple-ish terms?)

 

[Brian Roth]

Connect the relay coil powering circuitry between +16 and -16. Add a dropping resistor in series with the coil if you can't find a relay requiring 32 VDC for the coil.

Bri

 

[JMan]

Connect the relay coil powering circuitry between +16 and -16. Add a dropping resistor in series with the coil if you can't find a relay requiring 32 VDC for the coil.

Bri

Oh, wow, I assumed it would be much more complicated than that! Now I’m not sure why…

 

[JMan]

Okay, I did some math and I'd appreciate it if someone would be so kind as to check it.

I'll assume a perfect 32vdc between my +/- power rails. (Real world might be slightly off but I haven't measured).

I'll use an Omron G5V-2-DC24 relay, which has a 24v coil rating and a coil resistance of 1,152 Ω.

Based on this, the coil current should be roughly 21mA (actually, I just realized it might be on the datasheet, and sure enough, 20.8mA).

So I need to drop 8 volts on my power rails. 8 V / 0.0208 A = 384.6 Ω. (Nearest E96 value is 383).

P = 8 V * 0.0208 A = 0.166 W (and I understand that best practices indicate that my resistor should be rated for at least double that)

So if I'm looking at this correctly, I think I would be okay to use a 383 Ω 0.5W resistor. Does that seem right?

 

[Brian Roth]

Looks good to me. 390 Ohms would be close enough fwiw. Half Watt good enough.

Bri

 

[JMan]

Thanks for the help!

 

[richiyobs]

The modules themselves have two separate ground paths: an analog ground on Pin-5 and a power ground on Pin-
13. These are routed separately through the backplane and are joined at the power input connector. The analog
ground must only be used for grounding actual audio signal. The power ground could be used for anything where a
ground is needed that does not carry audio.

so i routed my ground path in a wrong manner cause i joined both analog and power GND together...
for analog ground only signal path, right? and each component that goes to Gnd long that path... but doing so an external device plugged to input connector, could not interfere if not properly grounded?
instead power Gnd is for any active components that must be supplied with main dual 16V ....
in this way they are separated but have to be joined in one point to keep equipotential
sorry for my dumb questions but i still have a lot to learn about Grounding

thanks for your attention

best
edit- or Better the chassis since Is Wired to connectors solve the problem sharing same earth to external devices... Isn t It?

 

[Bobby Baird]

Pin 5 and 13 are connected together after the edac connector on the backplane of the 500 series host power supply input connector. Only issue with connecting them on the 500 pcb is you are potentially creating a ground loop. Think of chassis, ground, & 0V as tributaries of water flowing into a main body of water returning to the power supply. No need to route the water more than it needs to be.

 

[richiyobs]

I pin 5 e 13 sono collegati insieme dopo il connettore edac sul backplane del connettore di ingresso dell'alimentatore host serie 500. L'unico problema con il collegamento su 500 pcb è che stai potenzialmente creando un loop di terra. Pensa a telaio, terra e 0 V come affluenti d'acqua che scorrono in un corpo idrico principale che ritorna all'alimentazione. Non c'è bisogno di indirizzare l'acqua più del necessario.

Thanks for clarify It with a useful example

 

[JMan]

I see configurations like this on a number of 500 modules that I've encountered. I guess the diodes protect against reverse current, and the capacitors are for smoothing. Is this de rigueur when laying out a 500 module? Any specific considerations, or can one just drop in the pictured components and call it a day?

 

[richiyobs]

So each board has filter caps and protection on dual 16?

 

[JMan]

So each board has filter caps and protection on dual 16?

Many of the 500 modules that I’ve built that come as kits employ something similar to this, yes. I’m just wondering if it’s something that is always a good idea, or if it happens to have some idiosyncratic purpose specific to the individual circuits.

 

[dmp]

I see configurations like this on a number of 500 modules that I've encountered. I guess the diodes protect against reverse current, and the capacitors are for smoothing. Is this de rigueur when laying out a 500 module? Any specific considerations, or can one just drop in the pictured components and call it a day?

I had to look up de rigueuer: "required by etiquette or current fashion."

Yes - if you have the space it's a good idea to include these components. It's a best practice (versus a 'fashion')
The protection diodes stop a incorrect voltage connection from damaging the module. The caps help protect against a noisy PSU that may show up in the modules audio output. You also sometimes see series small resistors before the caps of ~10 ohms that help filtering and will fuse if overloaded.

 

[JMan]

I had to look up de rigueuer: "required by etiquette or current fashion."

Yes - if you have the space it's a good idea to include these components. It's a best practice (versus a 'fashion')
The protection diodes stop an incorrect voltage connection from damaging the module. The caps help protect against a noisy PSU that may show up in the modules audio output. You also sometimes see series small resistors before the caps of ~10 ohms that help filtering and will fuse if overloaded.

Thank you!

And you are right, de rigueur is not quite the right choice of words here, since although it means obligatory or as a matter of convention, it also implies a social characteristic in the subject at hand.

Regarding those small value resistors: would they be placed in series with each of the caps between the voltage rail and common, or some other configuration? I’ll look around at some schematics and try to spot an example, but this seems simple enough, and I do have the space for two extra resistors.

 

[Bobby Baird]

The caps help to lower the impedance on the power rails and provide better transient response.

 

[richiyobs]

Is the attached the right way for PSU filtering?
Thanks for your attention and support
Best

 

[JMan]

Going back to my question in the first post, which pin on the card connector (1, 5, or 13) would be the ideal place to connect an internal shield or ground connection of a transformer? I would think that an external shield like a mu metal case or similar would go to chassis, but would the same apply to something like pin 6 in the attached image, or would that be better off going to audio ground? I know there's probably a certain amount of "just try each and see if one gives better results," but since I'm laying out a board, I'd like to try to get it right as early as I can.

 

[Bobby Baird]

Is the attached the right way for PSU filtering?
Thanks for your attention and support
Best

This is a correct layout. I would be safe and use 25v rated electros for C1 & C2. The 10 ohm resistors may be redundent with the reverse protection diodes in place. With the diodes you will see about a .7 voltage drop with resistor it will drop further limiting headroom.