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Circuit building: stop using antique parts (2014)

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Re: Circuit building: stop using antique parts (2014)

#101

Post by jwatte »

PeanutNore wrote: post #30
ChuckMcM wrote: post #12

Sigh. I like FETs as much as the next engineer but if you're going to write about them, try to not make things worse. In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT. I was helping a high school student with a transistor project and he was complaining that "half the FETs he boug…

When I buy 100 BS170 MOSFETs, I also buy 100 9.1v Zener diodes for this precise reason. Gate protection diodes are essential for peace of mind when using MOSFETs.

Although I really wish there was a better alternative to the BS170 in the same TO package, because BS170, too, is old tech and has high Rdson.

Re: Circuit building: stop using antique parts (2014)

#102

Post by CamperBob2 »

jacquesm wrote: post #21
mrob wrote: post #17

Mechanical relays are not obsolete. They can have lower resistance and capacitance than solid state equivalents. A good relay is a very close approximation to a plain wire when closed. Relays are still commonly used for RF switching.

RF grade relays will cost you an arm and a leg though.

To that point, another mistake a lot of amateurs make is that they buy expensive things on DigiKey without looking on eBay first.

Re: Circuit building: stop using antique parts (2014)

#103

Post by jwatte »

bsder wrote: post #31
PeanutNore wrote: post #14

I build a lot of guitar effects, and that community is even worse when it comes to attachement to obsolete components. The discontinuation of J201 JFETs (in TO-92 through hole package at least) by Fairchild has caused a lot of upset. My perspective, not widely shared, is that JFETs in general have been made obsolete by depletion-mode MOSFETs, at least in audio circuits. Part of the reason, I think, is that a lot of "…

> My perspective, not widely shared, is that JFETs in general have been made obsolete by depletion-mode MOSFETs, at least in audio circuits. A guitarist friend decided to "test" me once and put this in front of me and ask what it would sound like: http://el34world.com/charts/Schematics/files/randall/Randall... My immediate response was: "That looks like a really great amp from the mid 1980's--looks like it was design…

ADC, MCU, DAC, done. Cheaper, too -- I think 50 cent ARMs can do that these days. Any pedal that isn't digital today is just nostalgia (like tube headphone amps and the like.) Digital is the clear better choice even for sound shaping.

Re: Circuit building: stop using antique parts (2014)

#104

Post by CamperBob2 »

dyselon wrote: post #42

Is there a good reference for potential upgrades to old, obsolete-ish parts? I definitely understand that many of the old logic ICs, transistors, and op-amps have been displaced by better parts, but I don't always know how to identify them short of a parametric search on digikey and hoping there's not some sharp corner I missed. I'd find a lot of value in a page that had some recommendations for "Are you using for ?…

Not really, because as so many commenters have pointed out, the choice to use "antique" parts is more of a value judgement than a violation of natural law.

When in doubt, your best move is probably to see what Horowitz and Hill have to say. AoE3 has a lot of specific component recommendations.

Re: Circuit building: stop using antique parts (2014)

#105

Post by Obi_Juan_Kenobi »

aexaey wrote: post #28
ChuckMcM wrote: post #12

Sigh. I like FETs as much as the next engineer but if you're going to write about them, try to not make things worse. In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT. I was helping a high school student with a transistor project and he was complaining that "half the FETs he boug…

Yep. It is indeed easy to ruin a FET with minuscule amount of static charge. That is, unless there is a zener (or two, back-to-back) connecting gate to source. Many modern FETs have this built right in. E.g. ATP214 [1]. [1] http://www.onsemi.com/pub/Collateral/ENA1712-D.PDF

That does sound like a very useful part for learning purposes, as well as general robustness, but they don't appear to be particularly common. I get no results on eBay, nor can I find through-hole packages.

Do you know of anything available like that?

Re: Circuit building: stop using antique parts (2014)

#106

Post by pravda »

failrate wrote: post #55
busterarm wrote: post #33

Earlier quoted context omitted.

Guitar d00ds having obscure, nonsensical reasons for things because "mah tones!"? Say it ain't so. I mean, nearly every tube head on the market has an essentially pointless standby/bypass switch because of the mistaken belief that you need to warm up your tubes for some arbitrary amount of time in a modern amp and keep them warm. I forget which manufacturer it was that dropped the switch on one model and saw sales pl…

If I ever made analog audio equipment professionally, I would add an entire series of switches and dials that weren't wired up to anything.

Just make sure the dials go up to eleven! For that one more, that extra push over the cliff.

https://www.youtube.com/watch?v=KOO5S4vxi0o

Re: Circuit building: stop using antique parts (2014)

#107

Post by nomel »

aexaey wrote: post #28
ChuckMcM wrote: post #12

Sigh. I like FETs as much as the next engineer but if you're going to write about them, try to not make things worse. In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT. I was helping a high school student with a transistor project and he was complaining that "half the FETs he boug…

Yep. It is indeed easy to ruin a FET with minuscule amount of static charge. That is, unless there is a zener (or two, back-to-back) connecting gate to source. Many modern FETs have this built right in. E.g. ATP214 [1]. [1] http://www.onsemi.com/pub/Collateral/ENA1712-D.PDF

Here's a great example [1] of using static charge to activate a FET, as a proximity detector.

[1] https://www.youtube.com/watch?v=HwC6EHah9xI

Re: Circuit building: stop using antique parts (2014)

#108

Post by TD-Linux »

AceJohnny2 wrote: post #83

I've recently gotten back into hobby electronics, trying to revive all that EE knowledge I haven't used in 15 years, and one thing I sorely lack is knowledge of common components to use. Online electronics stores are no help because of the overload of possible components. Is there some sort of Cookbook out there I could refer to for up-to-date examples of common circuits and electronic tasks? I mean, I otherwise tota…

A lot of manufacturers have parts designed as drop in replacements for older parts, sometimes even with similar looking part numbers. Another thing that I often do is use Digikey's search and check their stock quantity to find out what's "popular". For example, if I want an op amp, I'll go to that category on Digikey and then first enter a quantity and sort by price. Then I'll start adding constraints - for example, for a 324 replacement, I might want it to be through hole (I nearly always do SMD designs though). From that, I unsurprisingly find the LM324 (it's still one of the cheapest!). But I also find the MCP6002, which is lower voltage but has rail to rail inputs and is designed for a capacitive load - perfect for driving a microcontroller ADC.

The truth though is that it's not like the old parts got any worse, and are still often the cheapest choice. You have to add additional constraints (I want lower loss, better performance etc) for something else to be "better".

Re: Circuit building: stop using antique parts (2014)

#109

Post by jwatte »

busterarm wrote: post #35
PeanutNore wrote: post #14

I build a lot of guitar effects, and that community is even worse when it comes to attachement to obsolete components. The discontinuation of J201 JFETs (in TO-92 through hole package at least) by Fairchild has caused a lot of upset. My perspective, not widely shared, is that JFETs in general have been made obsolete by depletion-mode MOSFETs, at least in audio circuits. Part of the reason, I think, is that a lot of "…

Separate from my other comment. I'm pretty much switched over entirely to AxeFX for my guitar & bass setup these days but I've been building circuits lately and figure instrument & vocal effects would be cool projects. Any places I should get started looking?

Buy a Teensy 3.x and a pedal adapter kit.
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