Hey all, I'm planning to do quite a few builds in the near future that require the J201 and/or 2N5457. I've read some posts about this but wanted the opinions and experiences you all have had, what are good replacements for those 2 transistors?
the smd versions of them both on adapter boards work really well.
I can recommend chromesphere's store DIYGP. I've used his J201 SMDs boards and transistors a few times. They are a fantastic replacement.
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Quote from: flanagan0718 on September 16, 2017, 05:04:39 PM
I can recommend chromesphere's store DIYGP. I've used his J201 SMDs boards and transistors a few times. They are a fantastic replacement.
I can recommend it too.
MPF102 can be an excellent replacement. Not sure on the availability though. I bought my last batches of all of them when the EOL was announced.
Quote from: flanagan0718 on September 16, 2017, 05:04:39 PM
I can recommend chromesphere's store DIYGP. I've used his J201 SMDs boards and transistors a few times. They are a fantastic replacement.
I might have to try this. I've always tried to stay away from SMD, but I don't know if I have a choice now. I'll give that a shot.
Mouser carries 2n5457s in through-hole. Central Semi started making them. If you are willing to buy 10, they are 77 cents a piece. Not necessarily cheap, but if you have a SMT and an adapter board, that adds up, too.
This sort of mimics what Pickdropper is saying.
Smallbear has both transistors. I use the SMD equivalents of both. Soldering them is ok but it takes some getting used to and a little time (chip on board and then the 3 leads). The chips are tiny. Depending on how many you need I would really look at the price difference and if you could live paying the .50/.55 cents for the real thing from Smallbear. If it cost you let's say .30 cents for the chip and board is the time you spend making it worth .20 cents. Of course I didn't factor in shipping costs (l believe you can get each SMD on Arrow with free shipping). Anyway just my half cent on the subject. '
From the last series of through-hole J201's I bought, 9 out of 10 where out of spec ... I had to swap with a few other builds (where I used them for buffering) to get a few good ones for an Azabache build. YMMV but I will try my luck with SMD components in the future.
I've been using 2n5485s and 2n5484s as replacements for 2n5457. There still seems to be a few around of those, and they work ok as far as I can tell. I've used them (without matching) in a couple of Phase45s, a BSIAB, and wherever else a 57 is spec'd.
Quote from: WormBoy on September 17, 2017, 12:38:25 AM
From the last series of through-hole J201's I bought, 9 out of 10 where out of spec ... I had to swap with a few other builds (where I used them for buffering) to get a few good ones for an Azabache build. YMMV but I will try my luck with SMD components in the future.
Did you get them from Small Bear or somewhere else? I had that experience with Tayda, but I assumed that Small Bear would have in-spec parts
Quote from: pickdropper on September 17, 2017, 05:11:32 AM
Quote from: WormBoy on September 17, 2017, 12:38:25 AM
From the last series of through-hole J201's I bought, 9 out of 10 where out of spec ... I had to swap with a few other builds (where I used them for buffering) to get a few good ones for an Azabache build. YMMV but I will try my luck with SMD components in the future.
Did you get them from Small Bear or somewhere else? I had that experience with Tayda, but I assumed that Small Bear would have in-spec parts
No, it was a webshop in the Netherlands. And, well, I think that technically they were still in spec (as the ranges on these JFETs are so wide), but only by a hair.
Please help me out with my understanding of in spec/out of spec. I always thought that as long as a build didn't call for matched sets then as long as the transistor wasn't dead it was good to use. Is this assumption on my part wrong?
Also, one other thing on the SMD chips. I believe if you were trying to match pairs/sets it would be more economical to go that route than to buy real ones, yes or no? I normally have bought pre matched pairs and paid extra before I bought a 100 SMD chips. From my readings the SMD chips don't vary as much as the real ones do, correct/incorrect?
The J201 and 2N5457 that I got from Smallbear recently were all in-spec. The 2N5458 that I got from Tayda a while ago (a year?) were also in spec for 2N5458 - the spec allows somewhat higher Idss than a 2N5457. Tayda hasn't carried J201 or 2N5457 for a while, presumably because they can't get them.
To see how types of JFETs compare, here is a plot I made of -Vp and I_dss for various JFETs that I had, measured using the simple Runoffgroove testing circuit (on the Fetzer Valve page). The sources of the transistors were:
J201 - smallbear
"off-J201" - a US ebay seller. I expected these might be dodgy. They are close to but not quite J201 spec.
2N5457 - smallbear
2N5458 - Tayda
2N3819 - old stock castoffs from an electronics lab
J113 - smallbear (J113 have very different specs from J201 etc)
Quote from: BrianS on September 17, 2017, 11:53:35 AM
Please help me out with my understanding of in spec/out of spec. I always thought that as long as a build didn't call for matched sets then as long as the transistor wasn't dead it was good to use. Is this assumption on my part wrong?
Depends on the circuit and how you define 'good' ;D. For a simple JFET buffer it might not matter much, but for a boost or overdrive ... An out of spec JFET will likely not give you the sound that the designer intended for the circuit, and it might not even bias properly with the resistors/trimmers that are in the design. There is a reason that a J201 will sound different in many circuits than a 5457, and that's because of specs ;).
PF5102 is a direct replacement for the J201. Still available.
Quote from: impycat1 on September 17, 2017, 12:30:06 PM
PF5102 is a direct replacement for the J201. Still available.
The Idss of that one is much, much higher ... even though Vgs is similar. I would not count on it as a direct replacement in general.
Quote from: WormBoy link=topic=26397.msg255878#msg255878 date=150567
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Depends on the circuit and how you define 'good' ;D. For a simple JFET buffer it might not matter much, but for a boost or overdrive ... An out of spec JFET will likely not give you the sound that the designer intended for the circuit, and it might not even bias properly with the resistors/trimmers that are in the design. There is a reason that a J201 will sound different in many circuits than a 5457, and that's because of specs ;).
Makes perfect sense. Thanks.
Quote from: BrianS on September 17, 2017, 11:53:35 AM
Please help me out with my understanding of in spec/out of spec. I always thought that as long as a build didn't call for matched sets then as long as the transistor wasn't dead it was good to use. Is this assumption on my part wrong?
For a crude explanation, the V_gs is the voltage of gate below source at which the JFET begins to conduct, and this can be from about -0.5 to -several volts depending on type. And the Idss is the current through the drain and source resistors when the gate-source voltage is zero - this is typically from <1 to several milliamps depending on type. See the plot I posted on the previous page for some typical values.
Because the drain and source resistors are usually a few Kohms, the voltage drop across these resistors is Idss*R = a few volts.
Because we are working with low-voltage circuits with a supply that is often 9 V, there isn't much headroom - to bias a JFET amp stage into operating range, you want the drain voltage to be about 4-6V above ground, for example, and the drop across the drain resistor should be 9V minus that, so 3-5 Volts. What that means is, as WormBoy said, if you use a JFET that has too large I_dss, you might not be able to bias it properly (unless you make the drain resistance very small, which reduces the gain of the stage).
And if the JFET has a value of V_gs that is different from the design spec, it may not conduct when you want it to - this would mess up phaser stages, for example, and is why JFETs need to be matched for phasers. An amp stage doesn't need FET matching, but it still needs a gain as a function of input voltage that is similar to what the designer intended.
AFAIK this need to operate at low voltage is why pedal designs tend to use J201 and 2N5457, because those types have some of the smallest Vp and Idss.