Show HN: SevenFortyFun, a transistor level op amp kit | Hacker News Reader

Show HN: SevenFortyFun, a transistor level op amp kit

github.com

45 pointskumarski20 comments

Since I was curious enough to look: From the associated web site:

Analog has sort of kind of taken a backseat to our digital revolution, and the founders of O|A are upset about this. Our mission is to teach the world about analog, reclaim the forgotten domain, bring popular ICs to transistor level pcb kits, breadboard things, break things, care about transistor mismatches, worry about tolerances, and sometimes ask - why the heck is my circuit oscillating?

For what it's worth, I think your site makes a great introduction to your cause, but a poor introduction to your contributions to this cause. To someone already experience in analog hardware it's easy to get the reference that "SevenFortyFun" refers to the LM741, and why that's cool - but you probably should reach beyond that crowd if the first half of the site is to be believed...

Yes, a small link to the LM741 would have helped. Or maybe even a blown up 1:1 pinout, such as with the discrete 555: http://www.evilmadscientist.com/2013/555-kit/

A comment on hobby analog design in general. I recently got my ham radio license and in the studying process found the arrl handbook at the local library. This is a thick, heavy book full of information about circuits, antennas, waves, transmission lines, transceiver design, etc. for only $50. A college textbook like this would easily have been $200. I kind of wish I had know about it back in college.

The Art of Electronics by Horowitz and Hill can be had used off of Amazon for a similar price, and is also quite exceptional.

I think AoE is one of the best textbooks ever. Some of the sections in my edition (from 1983) are dated, but the basics are very well presented.

Agreed.

The second and latest edition of H&H is from 1989. In my opinion it has aged remarkably well. A third edition has been due out 'soon' for ages now - as of last fall rumor had it May 2014 would be the availability date - but at this rate it seems to be anyone's guess whether TAOCP, or Art of Electronics 3rd ed. will be completed first. In any case my expectation is that it will be worth the wait.

Who is this targeted at? As it stands, the documentation requires quite a bit of EE knowledge. If it's meant for novices, you'll probably need to define half the terms mentioned on the first page.

The other major issue IMO is instrumentation. Sims are fine for learning, but is the student going to have the satisfaction of characterizing GBW, slew rate, harmonics, etc? Is a computer sound card enough, and is it robust against beginner mistakes? That's the sort of stuff I would think about if I were you.

I had to do design and build almost exactly this for a lab in college (I did computer engineering and the first two semesters of analog design were required). It was impossible to make it work with discrete components like this due to things like uneven heating of the components. Now, in that class we were using a bread board and not a pcb and none of us thought to trim the leads on the components to keep it as neat looking as this. I'm curious how much of a difference that would make.

The electronics lab course that we took (in the physics department) placed some emphasis on designing circuits that were forgiving of the issues such as you cite. This led to circuits that were not as sophisticated as e.g., a modern op amp chip, but forced us to think pretty hard about how the circuit should behave.

Also, maybe the breadboard was a rite of passage. ;-)

The 741 has quite a few current mirrors for bias/gain, so the bias points would be much more sensitive to transistor parameter mismatch than to wiring neatness. Also, discrete PNP transistors tend to be different from the lateral PNP's in a bipolar transistor IC process.

I suppose the value in ordering such a kit is that the devices shipped are pre-matched etc, so the hobbyist may reasonably expect a first-pass success.

The 741 is dominant-pole compensated, so even if there were wiring-related phase shifts at high frequencies there will be no loop gain in that region to cause instability.

For those of us who can only count to one, what does this thing actually do? Or, perhaps the better question, what can one do with this kit?

Anything from a audio amplifier (a crap one at that) to a audio filter, to a analog buffer, a comparator, many things are possible. For more information check out http://en.wikipedia.org/wiki/Operational_amplifier

Ah the lost art of analog design.

Not a lost art, you just don't see those guys around here.

Electrical engineering with a focus in RF - there were many at my university, and they are vital to things like radios, SATA, and DRAM.

Indeed. Well, perhaps it is a bit of a lost art in the sense that an EE curriculum nowadays has to sacrifice so much deemed fundamental perhaps a few decades ago in order to squeeze in all the digital stuff... I for one am glad I still had subjects on transmission lines, basics of FEM modeling of electric fields, impedance matching, low power analogue electronics and a whole pile of signal analysis/processing stuff even though I wasn't in the RF stream.

At my uni, EE's studied strictly analog. Digital was the purview of the CE's (computer engineer)

I've often wondered if some lost arts represent niche opportunities. My username is apt. I'm keenly interested in analog, particularly precision and low noise circuits. I have a side business that makes a niche market product based on an analog circuit.

At my day job, I'm one of the few people left who is capable (or maybe just willing) to compute a formal noise budget for an analog circuit. At least in the instrumentation business, there will always be a need to get the analog signal from the sensor to the analog-to-digital converter with dignity. And understanding analog issues is sometimes vital to resolving those issues using digital processing.

Instruments have been my life.

It would be good to find out more about your efforts.

Radiotron was good for me.

Nachbauer pushed outward from there also, here's an announcement page:

https://groups.google.com/forum/#!topic/rec.audio.tubes/swgQ... (his early links are long dead)

Here starts one preamp discussion:

http://www.ampage.org/homebrew.cgi?cat=sg&sb=&so=hl&page=989...

If you like, then here is the rest of that story:

http://www.dogstar.dantimax.dk

And don't forget this:

http://www.dogstarmusic.ca

With lost artists go lost arts.

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