Transistors vs. op amps vs. ICs - what's best for SS DIY guitar tinkering?

[UsableThought]

Trying to decide which way to lean in learning about SS amp design. And it may seem silly but I am wondering how the availability of the different kinds of silicon affects this.

- E.g. I read somewhere recently that transistors of the kind used in older amp & pedal designs are no longer even made - and that the ones we buy are old stock. I don't know whether this is crazy Internet rumor or sober truth nor how I could find out. This might affect for example delving very far at all into adapting any of Nelson Pass's DIY designs, or even one or two of Rod Elliott's.

- And how about op amps - are they still being made in plenty?

- Also, I read in my out-of-print edition of "Art of Electronics" - but can't find the reference verbatim at the moment - that a hazard of designing with ICs is that the particular IC you built your idea around has abruptly gone out of manufacture. As a possible example, DigiCom no longer stocks the 18V version of the LM386 and though Mouser has a few, they're end-of-life.

I'm VERY far from actual designing - a couple of light years out - but if I am going to go through the trouble of learning, well OK I understand that learning about the transistor comes first regardless; but even so I would like to know whether new building is being affected by the above questions.

[Enzo]

All manner of silicon is available and not likely to go away.  VERY common in the 1980s was a 4558 op amp.  You can still get them, but most amp makers have moved on to 4580, or even newer.  In MOST cases they are interchangeable, in a very few cases it may make a small difference.  TL072 is a very common op amp, and in most cases they will swap with a 4558.  There are other  less common types like 2068.  I happen to stock all those in my shop, but if I were a home tech, I might just have a drawer of TL072 and 45xx.  There will always be dual op amps, so even if newer types become the common ones, they will almost always work in place of the older ones.  Any audio thing you buy is going to have op amps in it.  Hell, there is a whole sub-genre of guys swapping big name special op amps into their stuff.  Burr Brown is a popular upscale name.

You need to study both.  There are some amps using "chip amp" ICs - power amps in one IC package.   But most SS amps still use discrete transistors.   SS preamps largely moved from transistors to op amps, but there are still plenty of transistor amps out there.  Old ones, and brand new ones, like Peavey Transtube series amps.

The transistors that are no longer made are the old germanium ones.  silicon works much better and more reliably.  The place germanium shined was in old fuzz tone pedal circuits.  If you want to specialize in that, then start collecting old Ge transistors.  That is, germanium, not General Electric.

SIlicon transistors?  There are millions.  Some very old types are not common in the market, but the beauty of transistors is you can substitute myriad others and it works fine.  There will always be small signal transistors, if you can't find a 2SC123, then a 2SC456 will probably work just as well.  Yes, I made up those numbers.  There are high voltage transistors like the MPSA42 and low voltage like the MPS8088.  But there are boocoo others that have equivalent specs.   I will bet my lunch money that any small signal transistor you come up with, I can find something in my drawers that will take its place, and you'll never hear a difference.

Unless a chip is unique, and your application is as well, don't worry about ICs going away.  If it serves any common purpose there will always be a selection of them.  if it is something real specific, like a floppy disc drive controller IC, well, what are you doing designing floppy drives anyway?  Or NTSC TV circuits, or dial up modems?  If they stop making 18v LM386, try adapting to a 12v version, or create a small discrete stage.

When we talk to engineers about designing with end of life products, it isn't the same as our use.  They concern themselves with very small nuances of design, and there may be some critical parameter concerning capacitance of load or some such that matters in their data circuit ,but not in our fuzz pedals.

[Loudthud]

Many semiconductor manufacturers are discontinuing products that have low sales numbers. Frequently it's the through hole version that gets the axe first, OEMs only use the surface mount versions and that's where the big sales numbers are. Some of the new parts that get designed are never made in through hole versions. There are little adapter boards that you can solder surface mount IC's to for prototyping.

[UsableThought]

The transistors that are no longer made are the old germanium ones.  silicon works much better and more reliably.  The place germanium shined was in old fuzz tone pedal circuits.  If you want to specialize in that, then start collecting old Ge transistors.  That is, germanium, not General Electric.

Thanks, all that info is very helpful.

I realize now that what I read about transistors going away must have been a comment exclusively about germanium & it would have been obvious in context had I known. If I remember it was an old fuzz tone being discussed.

Also I'm remembering too (my memory is like an electron, it moves slowly, not at speed of light) that with the "Art of Electronics" comment, they were talking only about extremely esoteric ICs and saying that it was safer to design with those that were a bit more generic.

[UsableThought]

Some of the new parts that get designed are never made in through hole versions. There are little adapter boards that you can solder surface mount IC's to for prototyping.

Thanks, also useful to bear in mind. I had read about the adapter boards on someone's blog recently & didn't quite get it - now it makes sense.

[J M Fahey]

You are partly right: *a LOT*  of TO92 (through hole) transistors are being discontinued this year, notably by ON (ex Motorola) .
That said, smaller manufacturers will continue making them because they are still being used, just not as massively.

There's a new company (Central Semiconductor?)  which apparently buys discontinued dies and processes and keeps making them, at 4X the price, of course.

Which means, say, 24 cents instead of 6 which is a deal breaker for a manufacturer but not a hobbyist.

The internal die is always the same, be it a:
metallic BC107


plastic short leg BC147


TO92 BC547


SMT BC847


so absolute worst case somebody with an unused backwoods shack can buy the dies unmounted and encapsulate them in any package he wants and serve a niche market.

FWIW our friend the Russian Tube Emulator designer, who was so kind as to post his PCBs here, used mixed technologies: boards are basically through hole designs for easier hobbyist experiments, BUT a few transistors, advanced modern FETs are available *only*  in SMT packages, so he designed the proper pads and they are mounted *under*  the PCB.

Not hard to build because 95% of parts are through hole and then you add a few Fets on the track side.

Hand building a full SMT parts PCB is possible, of course, but slow and annoying.

[Enzo]

I used to use MSPA06 a lot.  Good voltage and current for a small transistor, and I used them as relay drivers, and other control functions.  of course they also work for audio.  I would buy them by the 100.  At Mouser currently, the Fairchild ones are 49 cents each or 11 cents each in 100 lot.  The MCC are 28 cents each, and under 8 cents in 100 lot.  So for $8 I can get 100 or I can get 28.   I chose the 100.  Last time I bought some, they were 4 cents.

other common types are the same deal.  Or resistors, or caps, or whatever.   I can buy resistors for 15 cents each, or for a little over a dollar I can get 100 of them.

If peavey orders a million (literally) 2 cent transistors, and they go up to 8 cents, that is a big deal for them.  That is $60,000.  But for you or me, it is just pocket change, and in many cases, we will be passing the cost along to a customer anyway.

[UsableThought]

Some of the new parts that get designed are never made in through hole versions. There are little adapter boards that you can solder surface mount IC's to for prototyping.

So okay then . . . I may need to get some of these little adapter boards.

The active preamp schematic by voltwide, over in the active guitar thread he started, calls for a couple of transistors of this sort, which DigiKey and Mouser have only as SM.

I am guessing I should match up the stated style or type of surface mount to an appropriate adapter. For example the data sheet for the 2sk3557 transistors has this cryptic line under "product info":  "EITA, JEDEC : SC-59, TO-236, SOT-23, TO-236AB." So when I go DigiKey, they have only one adapter in stock for SOT-23 to DIP . . .  but they do have it, albeit it costs nearly $3.

A couple of questions -

1) Any best place to get these boards? Or just wherever I am getting whatever else I am getting?

2) There's really no way for me to do this other than adapter boards, right? As a DIY'er I only have perfboard to mount to. There are DIY methods  - Cheap/Easy homemade SMD-to-DIP adapters - but they seem like a real PIA.

[Enzo]

As to the cryptic line, it just describes the package.  If you google SOT23, you will see photos of that shape, plus dimensional drawings.  Or google TO236 for similar.  SOT - small outline transistor, similar to SOIC for small outline integrated circuit.  TO - transistor outline.   JEDEC is a standards organization.

I am not in the market for those boards, so I cannot assist for a source.


If you want to build a circuit, learn about substituting parts.  Some latest type JFET may come in only the sm variety, but other equivalent parts will exist in through hole.  JFETs have been around a long time.  Same with BJTs, there may be some new low noise transistor, but ther were low noise transistors decades ago, and if the new shape is inconvenient, the older types will still work in the package we prefer.

I like to cook, and if I see a recipe for biscuits that says use two cups of Gold Medal All Purpose Flour, and a half cup of Crisco shortening, I am happy using my store brand flour and some lard.  I have an inlaw who cannot make a recipe unless she has EXACTLY what it says on the card.

Transistor circuits are remarkably tolerant of substitutions, it is not at all like tubes where a 12AX7 and a 12AU7 are fundamentally different.

[UsableThought]

Grumble . . . well, I have been looking. In his quick-and-dirty guide to substitutions, RG Keen says the following - and I assume this was before through-holes started dying off quite so fast:

JFETs present a bigger problem. N-channel JFETs vary all over the map, and by an almost intractably large amount. The big problem is that the variation of Vgs and gm values is huge for these parts. This is one place that you may have real problems. However, almost all JFET circuits are set up with trimmer resistors to adjust the operating conditions for the JFET because of the large variation in the JFET. I personally stock 2N5485 and 2N5457 JFETs. BF244C is almost exactly the same as the 2N5485.

But I know it's good for me to start thinking about the part this way, so I'll see what I can find.

[Enzo]

yeah, there is no free lunch anymore.

JFETs can be all over, but the 2N5485 example is in stock at Mouser for $1.19 each.  20 cents cheaper in 10 lot.  So you invest $10 for ten of them, and sort through them to find a couple you like.  The rest can be used in common applications like channel switching, where gain and linearity don't matter.

[J M Fahey]

I buy them in 100 lots, the cheapest I can find, and spend an hour listening to some nice music and matching them.
I measure Vp, the voltage needed to cut them off, or in my case voltage needed to pass some given current (I choose 1mA because that's a nice preamp stage idle current value, similar to 12AX7 typical stages) .

* those measuring 1.8V or lower get in the "Preamp Fets" box (or Enzo's card envelopes)
* 3.5V or higher:  "Audio Switch FETs"
* around 2.5V :  "general purpose FETs"

Cheap FET du jour varies, but today just checked Mouser:

100    J111 for U$7 (yes, 7 cents each).  144000 in stock.
100    J113 for U$12.30   .....  12000 in stock
100    J112 , again for U$12.30   .....  over 3000 in stock

these are labelled "RF" which tells me they shouldmake better amplifiers than the above labelled "switching"
100 J211 for u$13.9

As you see, it pays to buy 100 (big discount)  and select.

You waste none, lower grades are great for mute/switch/compress  or phaser/tremolo/autowah use , only condition is to select similar ones ... easy if you have 100 of them.

J201, 2N5254 and other classic, audio grade types are no longer made so prices skyrocket, only "switching" types are really being made today, and some RF types, so we must use whatever's available.

Note: all of the above are through hole TO92 package.

[UsableThought]

J201, 2N5254 and other classic, audio grade types are no longer made so prices skyrocket, only "switching" types are really being made today, and some RF types, so we must use whatever's available.

Well, I am going to take Enzo's advice (& yours) and do some research & look around for myself - it's one way to force myself to slow down a bit & learn a little bit.

However regarding above, ON at least, and probably others, seems to be telling customers it is still making fabulous audio types - only just SM like the ones voltwide shows in his schematic. If through-hole quality goes down another notch would you not think of occasionally using SM audio types? Or is circuit design still more important & can compensate enough?

[Enzo]

I don't know that quality has gone down, just quantities.

I am glad Juan found the 7 cent JFETs, I was going to find cheap ones to suggest $7-8 for 100 and sort them, but went with the example you already had up.

Sure it makes sense to learn how to use sm stuff.  You can buy little adaptor boards, but if you bite the bullet and learn to make your own little boards, then using sm is a lot less challenging.

But in my mind, learning how circuits work, and how to design on them, is a lot easier with the larger parts.  A lot easier to me to get a volt meter or scope probe connected to a part leg.

Circuits are circuits.  Jfets are Jfets.  Changing a throughhole design to surface mount is just a matter of layout, mostly.

SM is how commercial electronics are made.  Cottage electronics - soldering in your basement - is not even a blip on their radar.  Commercial designers are looking for SM parts, and that is what the semi houses produce.

[voltwide]

The main problem with SMD are our degenerating eyes.  Equipped with a pair of high magnifying  spectacles and a 2mm solder tip with my 50 years old weller soldering station I solder prototypes on perfboard  including SMD0805/0603, Mini-Melf and SOT-23. Considering ruggedness against EMI (cell phones!) the smaller dimensions of SMD are superior to THT solutions. And populating a proper layouted SMD-PCB does not take more time than a THT-Version.
just my 0.02€