@djsundog Would I be correct that you've got some experience with analog audio electronics?

@djsundog The electronics guru at our makerspace has found himself thwarted when trying to help recent visitors working on analog projects. Seems knowledge of op amps is hard to come by these days. (He's more the FPGA generation.) I suggested we needed to extend our collective network of subject matter experts to draw on next time someone came in with such a project.

So, of course, I thought of you. Mind if I fly a recent visitor's project problem description by you to see what you think of it?

@beadsland I've been inactive for long enough to probably not be useful much, but I am willing to listen and tag in @Ricardus for more relevant background

@djsundog @Ricardus I've never learned to ride a bicycle, but perhaps it's like that, eh?

Here's what I've been told:

"The exact problem was amplifying the voltage of a 2 MHz sine wave form from a signal generator, then buffering it so it can source a couple of amps, with minimal phase noise and other noise"

Apparently, despite perusing data sheets and referencing Horowitz & Hill's Art of Electronics, the waveform they were getting was the wrong shape.

Initial thoughts? (Feel free to RT.)


@djsundog @Ricardus Re wrong shape:

"I don’t remember the details, but: it’s supposed to be a sine wave on the output. Or was it a square wave? And it’s … very much not, a totally different shape Still periodic, correct frequency

"Looked more like an ECG
There was nothing totally surprising about it, it was wrong in an expected way
But we had no idea where to start - does the op amp not have fast enough rise time
Is the op amp circuit not suitable to this frequency Are we hitting the rails"

@beadsland @Ricardus yeah, deffo out of my wheelhouse but I'm interested in the resolution (this might be a pun but if so it is unintentional)

@djsundog @beadsland @Ricardus I *might* be able to contribute here. Does a picture of the output exist? Is there a schematic for the circuit I can study? No guarantees I can help, but I do have some analog experience. Maybe a 3rd pair of eyes can help!

@djsundog @beadsland @Ricardus Also, how is the circuit built? Sometimes how components are placed or laid out can have surprising influences on circuit behavior.

@vertigo @djsundog @Ricardus We've reached out to the visitor. There was a schematic for the op amp part of the circuit, but the buffer was improvised. Please stay tuned.

@beadsland @vertigo @djsundog The Op Amp certainly could be an issue. Slew rates and what not are always published. But you're dealing with such high frequencies there are probably special problems that arise that are unique to that domain. I work in audio frequencies so I'm a bit out of my league here. Someone must know out there somewhere in the Fediverse!

@Ricardus @vertigo @djsundog Yep, they certainly went down that path when troubleshooting ("most of the evening", I'm told).

Any recommendations on resources for checking/diagnosing slew rates, to help a beginner avoid missing any obvious steps in the process? Or, alternatively, expend time unproductively on puzzling out diagnostic steps they don't clearly understand?

@beadsland @vertigo @djsundog I Since I don't work at those frequencies I don't know of anything except checking on various social media. IRC has #electronics channels, and ohter social media has groups for this kind of thing.

@Ricardus @vertigo @djsundog LOLOL Of course, that would be the suggestion when I suggest to my fellow maker, "How about we leverage social media to get some answers?" A recommendation on social media that we try social media. How very on message. :)

@beadsland @vertigo @djsundog I am literally in several Pro Audio DIY groups on evil Facebook, and on a forum called GroupDIY where I've gotten lots of help. So I'm suggesting you find the high frequency equivalents. 🙂

@Ricardus @vertigo @djsundog

IRC does have the advantage that its extant userbase might skew more toward the generation of those who came up during the heydays of op amp technology.

I suppose Facebook has its share of greybeards too. Too bad AOL message boards aren't such a thing anymore, eh?

@beadsland @vertigo @djsundog I go back to the Compuserve message boards! 🙂

And BBS's of course. Which is how I know @djsundog

@beadsland @vertigo @djsundog Has some vestige of Cserve survived beyond its death in 2009?

@Ricardus .@vertigo @djsundog The big drawback we face is that such forums are so siloed. I miss the days of Usenet. Cross-posting was a bane, but it also allowed for cross-pollination of knowledge.

The fellow I'm posting this electronics problem on behalf of is wondering if we wouldn't benefit from using Discourse rather than Slack, to get better threading. I'd rather an ActivityPub solution that supports long-lived threads but also federates like Mastodon to allow inter-forum crossover.

@Ricardus @beadsland @vertigo @djsundog

maybe look amongst circuit design for the 160 metre amateur radio band, and/or MF/AM broadcast radio - this is in the frequency range this project is dealing with.

I'm not sure if the average op-amps will work reliably at that rate - before Radio Caroline got their licence I was considering building a small AM transmitter to use with my old transistor radios and found it was a lot more complex than I'd expected..

@vertigo @djsundog @Ricardus Funny you should ask that:

"I’m sure the person who can help would like to look at the waveform and might instantly know what the problem is, and I wish I had kept a picture he sent."

I'm asking if there was a schematic. This is a problem brought into our space a month or so back, so information may be sketchy. But am posting here in the hope to find third pair of eyes to tag in when in the future a visitor arrives with a similar problem. So thanks for chiming in!

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