Guard Rings on PCBs (2023 Update)

For DC leakage, probably not.

We just did a bunch of boards as test cases for various no-clean fluxes. The worst one so far was 0.3e12 ohms between all the alternate pins on a d-sub, after a 100% humidity soak.

What part is involved? How much does leakage matter?

I do sometimes actively guard a part or a pad *from below* with an inner-layer pour, to reduce capacitance.

You can bend the critical pin of a DIP package out into mid-air.

It's a NE5532; using it as a preamp for a dynamic mic instead of the previous choice of IC, which as you may recall was widely denounced here.

The datasheet does actually mention this technique. I'd have thought 'guard rings' and capacitance issues were the domain of RF, not LF audio!

Absolutely no reason for guard rings on that part.

THanks, that'll save me a huge amount of swearing. Now, these DILs have two op amps per package. Since I probably won't be able to screw enough gain out of just using one of them, how do you feel about using both in series to end up with ~0.5V p-p audio signal out of the 2nd one? Will there be a problem with cross-talk?

The signal won't cross-talk to itself.

Balance the gains maybe, as in 10*10 = 100.

Screw that. I could get more out of a single BJT! I'm expecting a good

4000+ *minimum* out of a pair - a hundred's no good to me. 100 out of both in series with each other?? I'm hoping you missed a couple of zeros off your figure here. Please tell me it was a typo.

That was just an example of how N*N = N^2, which maximizes bandwidth. I have no idea how much gain you want.

Don't be obnoxious to people trying to help.

Cursitor Doom wrote: =================

** Dynamic is too vague, nominate the actual mic. Balanced mic line or not ?

...... Phil

THAT was being obnoxious?? <baffled>

Anyway, you've already helped so don't sweat it.

Cursitor Doom wrote: ==================

** Listen you f****ng NUT CASE !!!

Cascading the halves of a 5532 with a total gain of 4000 times at 20 to 30 kHz will *guarantee* HF oscillation. Even guard tracks will not help.

WTF do you need so much gain for?

Wanker.

..... Phil

Yes, and I'm not surprised - even though you often call others out for being unnecessarily unpleasant.

/This/ time anyway. Next time?

Oh, you still have many ways to screw it up.

My, someone's a little cranky today! I'll just put it down to the side-effects of the shots you had. :-D

As always, an inaccurate and inappropriate conclusion.

It's only a newsgroup. It ain't life.

We went to lunch at a sit-down restaurant that is supposed to check our vaccination credentials. They didn't.

Good thing; I don't have any.

As ironically stated by the John Doe snipped-for-privacy@message.header troll in message-id <sdhn7c$pkp$ snipped-for-privacy@dont-email.me who has posted yet another incorectly formatted USENET posting on Mon, 16 Aug 2021 21:05:30 -0000 (UTC) in message-id <sfejuq$im9$ snipped-for-privacy@dont-email.me.

There's a situation where a guard ring on the first input might be useful. With such huge gain you may have problems with stray capacitance if you aren't careful. Of course, the capacitance with signals on the same layer is very low, but not zero. The devil is in the details and I don't recall the details of your posts from weeks or months ago. I want to say your signal source is pretty low which means capacitive coupling won't be so important.

What does your math tell you?

Yes, here too.

Implementing reliable vaccine certificates is a known hard problem, especially worldwide.

Such things have been unhelpfully politicised here. It doesn't help that the libertarians frame them as "vaccine passports", which provokes a violent immune response in some people.