Guard Rings on PCBs (2023 Update)

Well, quite. BTW, have you heard anything from Win? I haven't seen a peep out of him for several months - which is very unusual. I do hope he's OK. :-/

I haven't done any. I'm not a designer but rather an experimenter - and that gives me a hell of a lot more freedom as I don't have any specific client's figures to target and meet. All I have to do is bugger about until it works to my own satisfaction, then move on to the next project. John reckons I need to equalise the gain between the two stages, so in order to achieve 4,000, each amp only has to provide a gain of ~63 which should be a cake-walk provided I observe the layout guidelines in the datasheet. Not having to worry about guard rings is a big plus, because with my eyesight and muscle tremors I'd really struggle to implement that freehand.

I got an email last week from Paul H, and asked him if Win was ok. He said he was fine. I suspect the general noise and nastiness of this group drove him off, as it has repelled many other good electronics people.

I did a sort of interview with a guy yesterday who said that reading AoE inspired him to want to design electronics. I bet AoE has done a lot like that, affected a lot of people. Phil Hobbs' book has had the same effect.

But really, accusing me of being off by orders of magnitude is fighting words. Solder stations at dawn.

Good.

Thanks for letting us know.

[...]

Get a news client that has a good plonk function. XNEWS is excellent. I have

165 posters in my plonk file and find that SED is quiet and useful.

Now all we have to do is get some to trim their posts more often.

Larkin won't trim posts and he won't block very many posters. He is too much in love with hearing about himself. He loves to respond to people he has blocked by reading their posts in other people's replies. Do you not see that?

Larkin is one of the worst offenders here posting off topic in on topic threads and changing topics in any thread he wishes. He complains about off topic threads while starting his own. It is hilarious that you suggest he needs to block more posters! He couldn't stand the silence!

I meant to say your input is pretty "low impedance".

When I first began posting to Usenet back in the early 90s, it was the done thing and regarded as good netiquette to trim one's posts. Nowadays it's good practice as it saves others having to scroll down pages and pages of guff to get to the new bit, but back then it was also about saving bandwidth - which back then was expensive!

I do try to trim when possible, but there's a certain poster here who complains when I do so and accuses me of selectively changing the meaning of his posts by doing this! You just can't please everyone, it seems. :-(

Both! Low(ish) impedance AND low level in terms of amplitude. Fortunately the very high Zin of these op amps is easy on delicate signals like these.

John Larkin wrote: ================

** What a load of self serving CRAPOLOGY !!

There sure as hell is a *culture* of arrogance & pure nastiness on this NG and MOST others too. But the worst culprits *include* the likes of Winfield Hill, Phil Hobbs, John Larkin, John Fields and Bill Sloman.

Cos electronics engineers and techs are among the most *egotistical and narcissistic* people you are ever likely to meet. The more important they wrongly imagine themselves to be - the worse they become. Claiming they have been hard by is MASSIVE hypocrisy.

FYI: Only reason I have been here so long is that I stubbornly REFUSE to leave.

...... Phil

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** I see a lot of damaged audio power amplifiers - lateral MOSFET and BJT types.

Sometimes the Rc & Cs in the output Zobel are burnt to a crisp - sure sign of continuous oscillation at 20kHz or above. Most of these amps have 3dB down points at 40 to 60 kHz and a mid band gain of 40 to 50 times. One of the common scenarios for this is having the input and speaker cables fitted, running side by side for some distance and NOT terminated while the amp is energised.

Curious as to just how much stray C coupling would be needed do the nasty on the amp - I tried a few low value caps from out to in. To my surprise, all examples tested needed only 22pF to 47pF with the input attenuator set at near full.

So with a gain of 4000 ........

...... Phil

How far away is the dynamic mic, is the connection going to be unbalanced or balanced via a long cable? What kind of input levels are involved - Is it to pickup whispering across a room or is it handheld by a jazz singer with lips practically touching the capsule? What output is needed - is it feeding a power amp or a laptop sound card? What power supply is available? There are many aspects to consider.

Personally I have found a series-shunt feedback pair of two low noise NPNs (like 2N2484, BC109C, BC549C, 2SC732 etc etc) is a very flexible and forgiving configuration for microphone preamps either with or without a transformer.

piglet

THanks, Piglet. I'll keep that in mind.

I almost never use dual opamps. Singles can be plopped wherever they fit best, and there's no moral dilemma about wasting half an opamp.

TCA0372 is an exceptional dual. I wish it were a single SO8 with a power pad and a thermal limit that works.

<snip>

Any idea whether the L272/L2720 are better-protected?

Cheers

Phil Hobbs

I haven't tried it, but I can't imagine it's as botched as the On part.

We added our own current limit around the TCA, which was special-case really easy. One diode!

Not sure what that means. The input impedance of the op amp circuit depends on the op amp circuit. I also have no idea what is meant by "easy on" signals. The low impedance means interference, including capacitively coupled feedback, needs to drive more current to create an issue, but as I and others have pointed out such high gain provides a lot of drive from very little input signal and so capacitive feedback can still be a problem. Have you done any of the math to see what capacitance might be an issue?

Low pass filtering would help by reducing the gain at the higher frequencies. It is easy to add to the op amp circuit directly.