Newbie Questions; Left in dark in another forum

[cdwillis]

Welcome to the forum.

I use this cheap tester from amazon: https://www.amazon.com/gp/product/B08K3BGKXC/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

I didn't expect it to compare to a Peak Atlas, but it verifies most of the stuff I need like transistor HFE, pinouts, resistor values, cap values, etc. I don't mess with jfets much, but it will tell you the Vgs(off) and Idss. You may already know, but there are much more reliable places to buy parts. Tayda Electronics, Stompboxparts, Lovemyswitches, Amplified Parts, GuitarPCB, AionFX, and of course Pedalpcb. You can get legit jfets from GuitarPCB, AionFX, Stompboxparts, and Pedalpcb. Jfets I think are the sketchiest things to buy from nonreputable dealers because some of them are no longer in production in through hole form.

 

[geoffrey]

Welcome to the forum.

I use this cheap tester from amazon: https://www.amazon.com/gp/product/B08K3BGKXC/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

I didn't expect it to compare to a Peak Atlas, but it verifies most of the stuff I need like transistor HFE, pinouts, resistor values, cap values, etc. I don't mess with jfets much, but it will tell you the Vgs(off) and Idss. You may already know, but there are much more reliable places to buy parts. Tayda Electronics, Stompboxparts, Lovemyswitches, Amplified Parts, GuitarPCB, AionFX, and of course Pedalpcb. You can get legit jfets from GuitarPCB, AionFX, Stompboxparts, and Pedalpcb. Jfets I think are the sketchiest things to buy from nonreputable dealers because some of them are no longer in production in through hole form.

Many thanks! Yes, I do know about those places, and have used many of them; I was just impatient, wanted them fast, and thought I’d roll the dice

Haven’t tested them yet cause I’m out of town. Even if I got lucky this time, I won’t be taking that risk again. Better to be patient and get quality than risk wasting money on junk.

I’ll keep you guys posted on how things turn out here

 

[geoffrey]

Welcome to the forum.

I use this cheap tester from amazon: https://www.amazon.com/gp/product/B08K3BGKXC/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

I didn't expect it to compare to a Peak Atlas, but it verifies most of the stuff I need like transistor HFE, pinouts, resistor values, cap values, etc. I don't mess with jfets much, but it will tell you the Vgs(off) and Idss. You may already know, but there are much more reliable places to buy parts. Tayda Electronics, Stompboxparts, Lovemyswitches, Amplified Parts, GuitarPCB, AionFX, and of course Pedalpcb. You can get legit jfets from GuitarPCB, AionFX, Stompboxparts, and Pedalpcb. Jfets I think are the sketchiest things to buy from nonreputable dealers because some of them are no longer in production in through hole form.

I just went ahead and bought that tester you recommended. Thanks again.

 

[geoffrey]

UPDATE: So I switched out the 2N5457s in Q1 and Q2, and left a 2N5457 in Q3 (This was suggested as an option to experiment with in the build document). I then followed @temol's instructions above and...success! I was able to get all 3 transistors int the 6-6.5v range, solving my lack of a clean boost problem and the pedal sounds great. However, there is one thing I'm curious about regarding these results:
No matter where I set the trimmer, I was only able to get all 3 transistors in this range of 6-6.5v. I thought I would have more range than that to experiment with. Does this signify anything?

Thanks everyone here for your help. I'm sure I'll be back on here bothering you all again with my next novice issue soon.

And by the way, the 2N5457s I got from Amazon work fine. Got lucky this time, but won't roll the dice there again

 

[giovanni]

Glad you sorted it out! The voltage range you see may be due to the design of the circuit around the transistors specs. I’d have to look closely at the schematic to tell for sure.

 

[temol]

No matter where I set the trimmer, I was only able to get all 3 transistors in this range of 6-6.5v. I thought I would have more range than that to experiment with.

With the values from the schematic and (legit) 2N5457 you should be able to set wide range of drain voltages. Can you measure Vp of the transistor?
Let's clarify.. you're able to adjust drain voltage only between 6V-6.5V or you can't go below 6V?

On the schematic there's a resistor between volume potentiometer and GND so you cannot go all the way down to zero with the volume... quite unusual.

 

[geoffrey]

1. Please forgive my ignorance, temol, but how do I measure Vp? Pedal building is my first foray into the world of electronics; and although I'd like to think I'm off to a good start, I've come into this knowing next to nothing.

2. Yes, I'm able to adjust drain voltage only between 6V-6.5V...I can't go below 6V.

3. Your observation regarding the resistor between volume potentiometer and GND interests even a beginner like me. Is this just an aside, or is it relative to my drain voltage situation?

Thanks for taking the time to help me learn!

 

[kristopher]

I too built that 3 Transistor Champ of a circuit, some time ago. I believe I went with J201's. But I haven't decided where to use it. It's such a small board that I plan to cram it into another pedal. It's always fun to have an extra boost in the path. In fact, a lot of the boards from that other pcb supplier are great for that. Small add on boards can be a blast.
Also, this is a great forum for learning and sharing. Welcome to the fold.

 

[temol]

1. Please forgive my ignorance, temol, but how do I measure Vp?

You need a power supply (or a battery), multimeter and transistor. Connect positive terminal of the power supply to pin 1 of the 5457, negative terminal to pin 3, and measure voltage between pin 3 and 2.

2. Yes, I'm able to adjust drain voltage only between 6V-6.5V...I can't go below 6V.

If the schematic you provided matches the circiut that seems to be odd..
Take a look


TR1 is 20k. So it goes from zero R to 20K. Zero R means you have VA on a drain of the Q1 (8.7V? 8.6V? It's 9V minus voltage drop of the D2).
With TR1 set to 20k, voltage on a drain should be much lower. Maybe 1V or even lower for the 2N5457. Unless there's a resistor between TR1 and Q1 you should be able to set voltage between 1V and almost 9V.
Maybe you put 10K instead of 1K for the source resistors (R3, R6, R9)?

3. Your observation regarding the resistor between volume potentiometer and GND interests even a beginner like me. Is this just an aside, or is it relative to my drain voltage situation?

It's not related to voltage issues . Just an observation.

 

[geoffrey]

I too built that 3 Transistor Champ of a circuit, some time ago. I believe I went with J201's. But I haven't decided where to use it. It's such a small board that I plan to cram it into another pedal. It's always fun to have an extra boost in the path. In fact, a lot of the boards from that other pcb supplier are great for that. Small add on boards can be a blast.
Also, this is a great forum for learning and sharing. Welcome to the fold.

Thanks for welcome, Kristopher! Yea, right now I'm using it as a boost, but it probably won't end up getting a permanent spot on my board. Don't get me wrong - cool pedal, and it was a good first build - but like you, not sure how to best use it yet. And I noticed the small add on stuff over there. Gonna check them out!

 

[geoffrey]

You need a power supply (or a battery), multimeter and transistor. Connect positive terminal of the power supply to pin 1 of the 5457, negative terminal to pin 3, and measure voltage between pin 3 and 2.
View attachment 37152



If the schematic you provided matches the circiut that seems to be odd..
Take a look
View attachment 37154

TR1 is 20k. So it goes from zero R to 20K. Zero R means you have VA on a drain of the Q1 (8.7V? 8.6V? It's 9V minus voltage drop of the D2).
With TR1 set to 20k, voltage on a drain should be much lower. Maybe 1V or even lower for the 2N5457. Unless there's a resistor between TR1 and Q1 you should be able to set voltage between 1V and almost 9V.
Maybe you put 10K instead of 1K for the source resistors (R3, R6, R9)?
View attachment 37165


It's not related to voltage issues . Just an observation.

Sorry for the late response - was hit hard by the flu. So, I went back to double check some stuff. Q1 (J113) I can adjust from 1 to over 8, which according to you is about right. Q2 (J113) and Q3 (2N5457) I can adjust from 5 to 6.5ish.

Someone on the other forum (who I believe is the creator of this schematic/board) said that this just signifies that there is a great amount of tolerance between transistors. I should ask him to expand on this, because I'm not quite sure what he means by this. Maybe you do, @temol.

I checked and I used the right resister and am going check the Vp later. The good thing is that I have a working pedal that sounds good. The fact that I can use this as a learning experience is a nice bonus. Usually, these learning experiences come via a pedal that doesn't work, not one that does

Thanks again for your help and knowledge, everyone. I'll be sure to do the same for others as I gain experience.

 

[fig]

Someone on the other forum (who I believe is the creator of this schematic/board) said that this just signifies that there is a great amount of tolerance between transistors. I should ask him to expand on this, because I'm not quite sure what he means by this.

If you take a look at the manufacturer's datasheet for those transistors, you'll find ranges of tolerances...for example the J113 Vgs-off tolerance is from -1v to -5v. This measurement is voltage between gate and source needed to turn off the device. This can be a crucial measurement when choosing transistors for picky circuits!

 

[geoffrey]

If you take a look at the manufacturer's datasheet for those transistors, you'll find ranges of tolerances...for example the J113 Vgs-off tolerance is from -1v to -5v. This measurement is voltage between gate and source needed to turn off the device. This can be a crucial measurement when choosing transistors for picky circuits!

Thanks, Fig. Yet something else I didn't know that I need to

 

[fig]

Thanks, Fig. Yet something else I didn't know that I need to

If you really have a hankerin' for that stuff, check out this article by resident @Chuck D. Bones

Thread 'JFET Biasing - part 1'
https://forum.pedalpcb.com/threads/jfet-biasing-part-1.5177/

 

[Chuck D. Bones]

Thanks, Fig.

More recommended reading:

https://forum.pedalpcb.com/threads/...now-about-jfets-but-were-afraid-to-ask.10464/

https://forum.pedalpcb.com/threads/why-are-jfets-such-a-pain-in-the-ass.4878/

Even if you don't understand those articles 100%, they should leave you with the clear understanding that JFET circuits are rarely, if ever, plug-n-play.

JFETs you buy on Amazon or eBay might be good, might be rejects, might not even be JFETs. You have to test 'em and demand a refund if they're not as advertised.

 

[geoffrey]

Thanks, Fig.

More recommended reading:

https://forum.pedalpcb.com/threads/...now-about-jfets-but-were-afraid-to-ask.10464/

https://forum.pedalpcb.com/threads/why-are-jfets-such-a-pain-in-the-ass.4878/

Even if you don't understand those articles 100%, they should leave you with the clear understanding that JFET circuits are rarely, if ever, plug-n-play.

JFETs you buy on Amazon or eBay might be good, might be rejects, might not even be JFETs. You have to test 'em and demand a refund if they're not as advertised.

Thanks, Chuck!