Half my J201s are bad?

[p_wats]

Long story short, it looks like half my through-hole J201s are bad. Short story long:

I was troubleshooting my in-progress Low Tide build, as it had farty, distorted output, which pointed to one of the JFETs. I assumed I had done a poor job soldering the surface mount 2Sk208, but my audio probe pointed to the through-hole J201 at the output stage. This was the first build that I didn't use sockets for the transistors, so it serves me right. Added a socket in that spot and swapped the J201, but it turns out only half of the ones in my stash actually sound right---the rest all have low output and sound farty and distorted.

I think they were mostly from Tayda over the years, but recall consolidating 2 batches into one bag at some point, so who knows.

In the attached photo the one on the left is bad and the one on the right is good (at least, it sounds good). Anyone else ever come across this?

 

[Gordo]

I've had bad J's before but in my case I think I might have cooked it while soldering. I don't recall having a whole bunch bad though.

 

[Laundryroom David]

Long story short, it looks like half my through-hole J201s are bad. Short story long:

I was troubleshooting my in-progress Low Tide build, as it had farty, distorted output, which pointed to one of the JFETs. I assumed I had done a poor job soldering the surface mount 2Sk208, but my audio probe pointed to the through-hole J201 at the output stage. This was the first build that I didn't use sockets for the transistors, so it serves me right. Added a socket in that spot and swapped the J201, but it turns out only half of the ones in my stash actually sound right---the rest all have low output and sound farty and distorted.

I think they were mostly from Tayda over the years, but recall consolidating 2 batches into one bag at some point, so who knows.

In the attached photo the one on the left is bad and the one on the right is good (at least, it sounds good). Anyone else ever come across this?

View attachment 54920

I’ve had problems with really inconsistent through hole JFETs from InterFET (bought via Mouser) but that said, I have not had great luck with consistency in through hole FETs in general. Exceptions would be buying from Barry at guitarpcb or if you bought a matched quad or something.

I’ve switched to smd for my fets since I got comfy with smd soldering. Way more consistent.

 

[temol]

Just measure Vp and Idss and you'll know. There is a lot of information on the forum on how to do this.

 

[p_wats]

Just measure Vp and Idss and you'll know. There is a lot of information on the forum on how to do this.

Yeah, thanks. More just curious if others have had experience with bad J201s in the same batch. I hear about fakes often, but haven't had a batch of a particular component where half were bad before

 

[jimilee]

I haven’t seen them at Tayda in literally years. I get mine from Barry w rut me he runs a sale.

 

[p_wats]

I haven’t seen them at Tayda in literally years. I get mine from Barry w rut me he runs a sale.

Yeah, these are ancient. Been hoarding them for a while. First time I've had issues using one from this batch, but I must have gotten lucky, as half appear to be bad.

 

[music6000]

Long story short, it looks like half my through-hole J201s are bad. Short story long:
In the attached photo the one on the left is bad and the one on the right is good (at least, it sounds good). Anyone else ever come across this?

View attachment 54920

They are probably on the border of being In Spec & Out of Spec.
As temol stated, you really need to measure jfet's Vp & Idds prior to installing to be sure.
This is more true now as what is available to purchase are leftovers.

 

[Coda]

As the other said, are they bad? Or just out of spec?…

 

[p_wats]

As the other said, are they bad? Or just out of spec?…

Haven't had the chance to actually measure them yet--just popped them into my Low Tide to see how they behaved.

I'd say a few sound more out of spec than dead, but most of the "bad" ones cause a huge volume drop and distorted signal. I'll do some actual measurements at some point and see what's what.

 

[Laundryroom David]

Haven't had the chance to actually measure them yet--just popped them into my Low Tide to see how they behaved.

I'd say a few sound more out of spec than dead, but most of the "bad" ones cause a huge volume drop and distorted signal. I'll do some actual measurements at some point and see what's what.

In the meantime … you know where to turn if you need a J201 or 2. I have through-hole and smd and smd on adaptor boards

 

[p_wats]

In the meantime … you know where to turn if you need a J201 or 2. I have through-hole and smd and smd on adaptor boards

Ha. Thanks! The good news is I have about 10 through-hole J201s that seemed fine, but will measure them all at some point to be sure.

Also seems like a good time to keep making the switch to SMD.

 

[Gordo]

Admittedly, I've switched over to smd as of late, just for the consistency. I keep a couple of thru holes around but I've been using smd's either directly or on adapter boards.

 

[p_wats]

Admittedly, I've switched over to smd as of late, just for the consistency. I keep a couple of thru holes around but I've been using smd's either directly or on adapter boards.

Yeah, makes sense. I've got a large stash of through-hole components, but have started dabbling in SMD more and more as that stash dwindles.

 

[p_wats]

Hmm. Finally made time to measure my J201s using the info on the ROG site, but my readings seem very off. Vp on most of them seems to be between 1-1.5v and Idss measures 0.100mA to 0.150mA (if I'm doing the adjustments correctly).

I've got one that seems fine (within the ranges on the ROG page).

Curiously half of these worked fine in my Low Tide, but half didn't, even though they mostly measure similarly. Maybe I'm doing something wrong?

 

[p_wats]

Thought I may have screwed something up on the breadboard, so I built the measuring layout as per this post, but still get the same, high measurements for almost all my J201s (even ones that worked fine in my Low Tide).

Any experts have any advice?

 

[p_wats]

For what it's worth, most of the ones that measure weird still bias OK and sound good in the Son of Ben and Supreaux Deux I just tested. Maybe they are at the high end of spec, but still good? Or maybe I made a mistake in my measurements both times?

Maybe an appeal to some of the experts like @temol @music6000 and @Coda can help shed some light?

 

[temol]

It's possible to set proper drain voltage even for the out of spec transistor. It's just a matter of the value of the drain resistor (trimmer setting).
Many pedals have 100k trimmers and because of that we can use almost any JFET. 100k it's a quite wide range of adjustment.
That's why you can set 1/2 Vcc with J201, 2N5457, 2n5458, etc. with the same circuit. This does not mean that the circuit will sound OK, despite the correct voltages.
The measurement values you provided are unusual for J201. How did you measure it? On a breadboard, on a PCB?

 

[p_wats]

It's possible to set proper drain voltage even for the out of spec transistor. It's just a matter of the value of the drain resistor (trimmer setting).
Many pedals have 100k trimmers and because of that we can use almost any JFET. 100k it's a quite wide range of adjustment.
That's why you can set 1/2 Vcc with J201, 2N5457, 2n5458, etc. with the same circuit. This does not mean that the circuit will sound OK, despite the correct voltages.
The measurement values you provided are unusual for J201. How did you measure it? On a breadboard, on a PCB?

Thanks. I initially threw something together on a breadboard based on the ROG site schematic, but then built a little measurement board on vero based on the layout in this post. Same results with both methods.

Maybe I'm doing something wrong with my DMM? I just have it set to measure DC volts.

That said, there is one J201 that measure within "normal" spec and it's in the only one that looks different. I traced my bag of J201s to a few orders from Tayda and Smallbear back in 2012, before there was so much concern about fakes and have used them in many pedals without issue (the Son of Ben and Supreaux Deux boards I just populated sound good to my ears too, for what it's worth).

 

[temol]

Vp on most of them seems to be between 1-1.5v and Idss measures 0.100mA to 0.150mA (if I'm doing the adjustments correctly).

Are you sure about this 0.100mA? Maybe it was 100mV (0.100V)? That would be 1mA. I have some fake J201s with Vp around 1.4V and Idss around 1mA.