Circuit building: stop using antique parts (2014) • Hacker News Board

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

#31

Post by bsder » Thu, Feb 02, 2017, 7:30 PM UTC

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 designed by someone who actually understands electrical engineering. It should have a pretty clean. But if you overdrive it, the clipping on those JFET's is gonna sound like fscking buzzsaw trash."

He, of course, laughed knowing that Dimebag Darrell used the amp for precisely that buzzsaw sound. You would have to add lots of "clipping" components to get the same sound out of depletion mode MOSFET's.

Now, whether that's a good sound is open to debate. :)

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

#32

Post by marcosdumay » Thu, Feb 02, 2017, 7:37 PM UTC

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.

They also have a very ohmic resistance, and very little interference between control and load signals (except when switching) that semiconductors lack.

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

#33

Post by busterarm » Thu, Feb 02, 2017, 7:41 PM UTC

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 "…

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 plummet and got freaked out support calls asking why the switch wasn't there. Next iteration had the switch back.

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

#34

Post by pravda » Thu, Feb 02, 2017, 7:51 PM UTC

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…

>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.

Not sure why that made you sad (extraneous ' in its?).

But I agree about the static-sensitive disadvantage of MOSFETs.

Also, the author mentions that a TIP120 is not a transistor but a darlington pair (two transistors in one) but then misstates the Hfe.

The whole point of a darlington is to get a high Hfe (small base current controlling large collector current) and the Min. Hfe is 1000, at least according to:

https://cdn-shop.adafruit.com/datasheets/TIP120.pdf

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

#35

Post by busterarm » Thu, Feb 02, 2017, 7:51 PM UTC

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?

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

#36

Post by earlz » Thu, Feb 02, 2017, 7:54 PM UTC

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 "…

I'm a noob builder (constructed my first pedal a week ago, woo) but I can kinda understand this. Most effects tend to overdrive their components. This by definition means that they operate beyond what a datasheet and the manufacturer specifies. Tiny differences that aren't noticeable when going by the specs can become much more obvious when hearing it overdriven.

Yes, the community is really based in "older is always better" kind of mentality, but there is a reason some old components are so valued, and why respected pedal manufacturers commonly hand-pick parts that meet their designed specs best (especially fuzz and overdrive effects), and this includes everything from picking transistors with ideal leakage etc, to hand picking resistors (though the resistor bit I'm not sure on why they don't just buy high precision ones for a few cents more)

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

#37

Post by ChuckMcM » Thu, Feb 02, 2017, 8:00 PM UTC

pravda wrote: post #34

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…

>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. Not sure why that made you sad (extraneous ' in its?). But I agree about the static-sensitive disadvantage of MOSFETs. Also, the author mentions that a TIP120 is not a transistor but a darlington pair (two transistors in one) but…

It wasn't the grammar :-) it was that the author considered the 10K resistor to ground as "not strictly necessary". It is critical if the microprocessor pin can float (tri-state). Without it, and a floating gate, not only will the FET eventually turn on, it can be damaged by excess charge build up.

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

#38

Post by mdb333 » Thu, Feb 02, 2017, 8:03 PM UTC

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 "…

True but i think a lot of that is in adherence to the original design/specs they're emulating (or straight up ripping off). Folks went nuts over the XVive BBD revivals or even still pay ridiculous sums for original panasonics. Sometimes there simply aren't alternatives to achieve the same circuit or you're repairing something very specific (although that's probably outside the scope of the article's PoV).

As well there's the vintage issue...Sure, I buy NOS caps from the 50-70s for guitar tone circuits. I doubt side by side they sound noticeably better but if you're building vintage it only makes sense to keep the 'tronics true to the time period.

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

#39

Post by mdb333 » Thu, Feb 02, 2017, 8:06 PM UTC

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?

I'm still resisting the AxeFx but being short on space and a growing stack of rack gear waiting to get fixed might push me over the edge soon :-]

There's a pretty classic book called Electronic Projects for Musicians that might be of interest: https://msu.edu/~dougl126/Electronic%20Projects%20for%20Musi...

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

#40

Post by karlkatzke » Thu, Feb 02, 2017, 8:07 PM UTC

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.

I use mechanical relays to switch AC power for pumps and similar AC motor loads using DC signals from Arduinos and similar.

I have very very little experience with electrical engineering (I'm in the Lego mindset of I plug things in according to things I find online until they work), but is there something I should be using instead with 120V ~3-5 A loads?