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Hey everyone. It’s been awhile since I’ve been on here. Heck it’s been awhile since I’ve built a pedal. But I recently built a preamp that includes a charge pump. It has 2n5457s which I need to bias. I bought what are supposed to be a matching quad set of Fairchild 2n5457s. Now with the charge pump installed I can not bias below 11v. Without the charge pump I can bias them to 4.5v. I’m assuming I need the charge pump in while biasing so the pedal is at operating voltage? I’m also connecting the + probe of my dmm to the drain of the 2n while my - probe is connected to ground. Is that also correct or do I need to connect the - to the source of the 2n while biasing? Or maybe I got ripped off and received some knock offs? https://imgur.com/a/HO52LNQ

A schematic would help.

There are counterfeit 2N5457 in circulation. We've been burned by them before. Through hole JFETs are getting pretty bad. You really need to have a semi-conductor analyzer in your tool box these days.

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*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Unfortunately the schematic has yet to be released by the person who has traced the original circuit. I’m assuming when you say sc tester you’re meaning one like the dca55 by peak? I recently purchased this https://imgur.com/a/Um8rxVF. Beside it are the 2n5457s, 2 quads sets. I blacked out the company name as not to cause any controversy with another company on this forum.
I figured since this circuit is using a charge pump to up the Voltage, then the bias would still need to be half of the current. I.e 9v so bias to 4.5. Although I’m not that knowledge about this. It’s my first build with a charge pump. Although the person who traced it has stated the transistors in the traced circuit were biased to 4.25. I purchased some mmbf5457s attached to jumper boards. Fingers crossed these are legit.

I'm not familiar with that unit. Does it tell you "n-channel JFET" when you test them? Do you get the same specs printed on the bags?

Those are probably legit 2N5457. I don't think someone is going to go to the trouble of printing off individual specs for each piece if they are fakes. You just need to be careful when you buy in bulk from Asia.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

This is all the info it gives for this transistor. https://imgur.com/a/1Ijwu1F
If these are legit, should I change my trimpots from 10k to a 50k or even 100k and try biasing them?

Daaamn, are you sure that’s right? If I’m looking at it, it measures at 24? That’s about 12 times higher than the average ones I have.


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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

All four 2n5457s are reading in the 20k range of hFE

The two 2n5088 are reading very close to each other. Here is one in the tester.

https://imgur.com/a/5YOG27u

The pedal doesn’t sound right. No matter the adjustment it sounds too saturated.

Well doing some more reading and hFE doesn’t apply to Jfets, doh

Your transistor tester is telling you that your Junction Field Effect Transistor (JFET) is actually a regular NPN Bipolar Junction Transistor (BJT). So if that is correct, then these are counterfeits. However, I'm not sure if that meter can read JFETs, so who knows? Most cannot, including the Atlas DCA-55...or at least the model that we have here in the shop. It's pretty old. Maybe they've updated it now. We recently purchased a semi-condutor analyzer that can test JFETs specifically for JFETs. If your analyzer can indeed read JFETs and those are legit 2N5457, it would say N-Channel JFET, otherwise they are fakes.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I went back and watched a review video of this tester. The person placed a mpf102 Jfet in it. The tester identified it as n-fet and gave I and the vgs reading. I don’t know if the tester could identify the mpf102 properly because of the spec difference or what. I actually went and pulled some j201s that I know are fakes and the tester read them as the same as the 2n5457s. Identified the j201s as bjts and gave gain and vf. I ordered some smd 5457s with adapter boards. I’ll test them on it when it comes in. Is it possible to get vgs readings on fakes? Just wondering if it’s possible if the place I bought them from matched them without properly identifying them as njets? I’m assuming no? A bjt 2n5088 spec sheet doesn’t list any vgs specs.

Well I got my mmbf5457s today. I ran it on my tester and it identified it properly.
https://imgur.com/a/ohx97NF

It makes me think someone went through a lot of trouble to sell me a match set of through hole fakes. I’m gonna try and build some jfet testers and see if I get close results to what was listed on these through holes.

They actually printed off labels with JFET specs for individually packaged parts? I've purchased fakes from vendors who I honestly don't think they knew they were fakes...they were just reselling from the person who sold the parts to them. And they've always refunded me. But this sounds pretty intentional. If you wanted to post a warning to other builders in the DIY discussion lounge, I wouldn't have a problem with it.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com