S.O.T J201

[myron tataryn]

Heads up! Bitsbox now have MMBFJ201 at 19p each,no brainer or what ?

[IvIark]

Yep, they're the ones to go for now.

[motterpaul]

Have you guys noticed any quality differences between these and older inline J201s?

[Beaker]

Thanks Myron. I will get some ordered ASAP.

19 pence each really is a no brainer - even if you have to pay 14 pence each for the boards, so 33 pence total price.

The 5457 are 34 pence each, which I thought was pretty good.

Get yourself some SMD paste flux like I describe in the "SMD soldering tips?" post, and it will make things a breeze.

Paul, the SMD JFETS are supposed to be made to a far tighter tolerance than the old through hole versions, so they should be much more consistent, effectively making matching a pair/set much easier.

The only possible downside that I can see would be if you need to use a gain figure that is outside the tolerance of the SMD versions. THen you might need to hunt through your through hole versions.

[Sensei Tim]

I've been using surface mount jfets for about 18 months now and I would not go back.

The only thing that I haven't tried is matching them for phasers and such.

[Muadzin]

Now if only those clever boffins who design DIY pcb's that reguire jfets would also include pads for SMT jfets. Then we wouldn't even need adapter boards. So far I've only seen one guy design pcb's with that in mind.

[pyreweb]

I was looking at the Surfy Bear reverb driver yesterday, and the engineer said that now he uses SMD JFETS instead of through-hole ones, he does not need to match them as the SMD versions have much better tolerances. He was talking about MMBF5457s, but would the same apply for all FETs? I am hoping to build a Phase 90 copy, and am wondering if I need to buy specially-matched 2N5952s or whether four normal SMD ones will be fine.

[Beaker]

"He was talking about MMBF5457s, but would the same apply for all FETs?"

In theory, yes. Maunfacturing has come an awful long way since the Seventies and Eighties, when many of these parts were made. As a general rule, parts are cheaper and better than they were then. Variations in the manufacturing process meant parts could, and would vary wildly, hence the plus or minus 25% tolerances what were typical.

Out of spec or failure rates could also be very high maybe 10%?


These days, the same equivalent part may be rated as +/- 10%, but actually measure +/- 2% - and that would be consistent right across a batch of a hundred thousand.

Out of spec or failure rates are now typically down to a fraction of 1%.

So to answer your second question, I think four SMD transistor will be fine.
However if you buy through hole versions, buying a matched set might be a good idea - either that or buy 50 and select the best four out of the batch!

[Sensei Tim]

What beaker said.

Most fabs today are using better quality silicon, and better/different doping and microfabrication methods to make SMD chips vs the old through hole parts.

Also, in the mid-80s Motorola started the whole 6-sigma quality management trend, meaning that the goal is 3.4 defects per million opportunities.   Like Beaker said,  even tho the spec may be ±10%, for all intents and purposes you're going to see a significantly smaller variation for any given batch.