# Newbie Questions; Left in dark in another forum



## geoffrey (Nov 23, 2022)

Hi All!
So some of you saw my first ever post and first PedalPbc build (VHS) in the build section the other day. This was my second successful build; my first build was with a board purchased from a competitor (who shall remain unnamed). Even though the build went well, I had some questions about the finished product; and so I did what most people would: went to their forum with my questions. Well, either their forum is dead or nobody wishes to help me, so since I received such a warm welcome from you guys the other day, I feel like I bring a few general beginner questions here and maybe get some help.

So this competitor’s circuit is meant to emulate
3 old fender amps of yore and simply has volume and drive controls. The drive packs a heck of a punch, as the description in the instructions state. But the description also says that it ranges “from a clean boost to overdrive”, however the thing is there’s nothing clean about even the lowest drive or volume settings on the one I built: it ranges from light dirt to pure filthy breakup. Don’t get me wrong, it’s pretty, but I wish it would start out as a clean boost as stated, and I’m wondering why it doesn’t. So my questions are 3:

1. The build contains 3 trim pots. Could how I set my trimmers have an affect on this issue? I know I installed them correctly, but I had no idea what to do regarding setting them afterword. I have never worked with trimmers before, so I just fooled around with the settings until I found the one I thought sounded the best.

2. Could switching transistors affect how clean/dirty it sounds? I used the 2N547 listed in the build instructions, but the instructions also suggested possibly experimenting with a J113, MPF102, or J201. How would switching the transistor up affect the sound?

3. And finally, could have I have done something wrong with the build to cause this?

forgive the long post and possible dumb questions. Keep in mind I’m just a beginner . I’m really disappointed I was left in the dark in this competitor’s forum. I’m not sure if I’ll shop there again. PedalPcb and this forum have really impressed me thus far, so I think I might stick around. 

Thanks in advance for your time and help! And if I should have posted these questions elsewhere in the forum, please kindly let me know


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## Robert (Nov 23, 2022)

Without knowing the circuit / seeing a schematic it's tough to say how you should set the trim pots.

In a lot of cases you start by adjusting the trim pots so the drain of each corresponding JFET (2N5457, J201, etc) measures a particular voltage, usually 1/2 VCC.   (4.5V for a 9V pedal, 9V for an 18V pedal, etc)


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## giovanni (Nov 23, 2022)

+1 to what Robert said. Hard to say without seeing the circuit but my guess is that if the transistors are not properly biased you may get more dirt. Also where did you purchase the transistors? There are many counterfeit JFETS out there.


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## geoffrey (Nov 23, 2022)

Robert said:


> Without knowing the circuit / seeing a schematic it's tough to say how you should set the trim pots.
> 
> In a lot of cases you start by adjusting the trim pots so the drain of each corresponding JFET (2N5457, J201, etc) measures a particular voltage, usually 1/2 VCC.   (4.5V for a 9V pedal, 9V for an 18V pedal, etc)


The instructions stated to set between 4.5 and 6.5. But no matter where I adjust the trim pots, I couldn’t get near those numbers, which is where my ignorance fully comes out into the open. Now I fear I may be testing or using my DMM incorrectly


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## geoffrey (Nov 23, 2022)

Schematic attached


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## geoffrey (Nov 23, 2022)

giovanni said:


> +1 to what Robert said. Hard to say without seeing the circuit but my guess is that if the transistors are not properly biased you may get more dirt. Also where did you purchase the transistors? There are many counterfeit JFETS out there.


I’m now embarrassed to say I purchased my 2N5457s from Amazon 

My J201s are from Mouser. I haven’t tried one here yet


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## temol (Nov 23, 2022)

What transistors did you install? Where do you connect DMM?


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## geoffrey (Nov 23, 2022)

temol said:


> What transistors did you install? Where do you connect DMM?


I installed 3 2N5457s.

I was told to put one connector on the middle leg of the trimmer and then the other on one of the other legs, and then repeat to see if I get the seem reading with each, which I do, but I am checking ohms here not volts with this process…at least
That’s what I was told to do by a veteran builder  

Also, should all 3 transistors be adjusted to the same setting?


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## geoffrey (Nov 23, 2022)

Low and behold, I finally just got a response from the other forum. Coincidence? Anyway here is the reply I got:
“Ideally you want to bias the 2N5457s to between 4.5v and 6.5v using those trimmers and a multimeter.  You’d power the pedal up and place the multimeter probe on the Drain of each 2N5457 the adjust the trimmer up or down until you get the correct value – the correct value depends on the 2n5457 (generally around 6.0v) and your taste (you could find that 5.9v is the magic tone or 6.2v is way better).  The way the board is laid out the Drain is the leg of the transistor closest to the bottom of the board. You would have to do the same thing if you were using J113s, MPF102s or J201s.”

Do you guys agree that this is the process I’m missing here? Makes sense, but is completely new information for me


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## temol (Nov 23, 2022)

Connect black connector to GND (for example negative connector of the power supply or barrel of the input/putput jack), red connector to drain of the transistor.  Measure voltage at marked points  - 1, 2, 3.


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## giovanni (Nov 23, 2022)

I would be wary of transistors purchased on Amazon. If you can’t bias them properly, they may be grossly out of specs. You need a transistor tester to verify them or some other method for measuring their specs.


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## geoffrey (Nov 23, 2022)

temol said:


> Connect black connector to GND (for example negative connector of the power supply or barrel of the input/putput jack), red connector to drain of the transistor.  Measure voltage at marked points  - 1, 2, 3.
> View attachment 36678


Awesome, Temol, many many thanks!


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## geoffrey (Nov 23, 2022)

giovanni said:


> I would be wary of transistors purchased on Amazon. If you can’t bias them properly, they may be grossly out of specs. You need a transistor tester to verify them or some other method for measuring their specs.


Yes, Giovanni, rookie mistake that won’t happen again. Then again, other than this “clean boast”
issue I’m on about here, the overdrive does sound pretty darn good, so maybe I got lucky this time 

I’m going to try out those mouser J201s later because at least I know those are legit. And yes, a transistor tester sounds like a must buy for me.


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## fig (Nov 23, 2022)

Most of the mods there, are members here. Nice folks. They're probably just busy with the holidays.


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## geoffrey (Nov 23, 2022)

fig said:


> Most of the mods there, are members here. Nice folks. They're probably just busy with the holidays.


You’re right, Fig. My excitement for my new hobby has led to impatience, which in turn has possibly caused me to come off the wrong way. I’m really not “that” guy. Scouts honor

If I offended anyone or sounded uppity by my “being left out in the dark” attitude, I apologize.

I’m very, very grateful for all your help!


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## fig (Nov 23, 2022)

I doubt anyone would see it as anything more than antsy-ness, and we've all been there!


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## Diynot (Nov 23, 2022)

Have you verified the values of the Source resistors (the 1k)? They are also responsible for biasing the 2n5457. If you aren’t getting the voltages to come into spec with just the trimmers wondering if there might be something amiss with those.


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## geoffrey (Nov 23, 2022)

Diynot said:


> Have you verified the values of the Source resistors (the 1k)? They are also responsible for biasing the 2n5457. If you aren’t getting the voltages to come into spec with just the trimmers wondering if there might be something amiss with those.


Yes, I verified all resistors before installing them, but now that you bring it up I’m going to double check.

Thanks for bringing this up…more knowledge for me to absorb 

I’ll keep you all posted. Probably won’t get to it until this weekend unfortunately because I want to get on it right now


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## temol (Nov 24, 2022)

One general commet regarding transistors.
For example - J201 counterfeits from ebay are most often rebranded other models. I have a lot of them, they work for me, but I don't use them where J201 is needed. They are ok as source followers (in buffers). So even if you have transistors from an unreliable source, don't assume that the circuit is not working because of the transistors. If it's JFET, the pinout is preserved, then there should be something on the output.
Of course, there is still the matter of setting the appropriate drain voltage - if nothing changes despite rotating the trimpot - maybe the measurement is made on a different transistor, or the wrong trimpot is set? Or an incorrectly mounted transistor. Or a problem with the source resistor.  Or....
If the range of drain voltage changes is insufficient (the voltage cannot be lowered enough) - increasing the value of the trimpot may help. But this may suggest that the transistor has parameters other than required in this particular circuit. If the voltage can't be raised enough - maybe there is a resistor in series with the trimpot (and minimal voltage is set by resistor value).


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## geoffrey (Nov 24, 2022)

temol said:


> One general commet regarding transistors.
> For example - J201 counterfeits from ebay are most often rebranded other models. I have a lot of them, they work for me, but I don't use them where J201 is needed. They are ok as source followers (in buffers). So even if you have transistors from an unreliable source, don't assume that the circuit is not working because of the transistors. If it's JFET, the pinout is preserved, then there should be something on the output.
> Of course, there is still the matter of setting the appropriate drain voltage - if nothing changes despite rotating the trimpot - maybe the measurement is made on a different transistor, or the wrong trimpot is set? Or an incorrectly mounted transistor. Or a problem with the source resistor.  Or....
> If the range of drain voltage changes is insufficient (the voltage cannot be lowered enough) - increasing the value of the trimpot may help. But this may suggest that the transistor has parameters other than required in this particular circuit. If the voltage can't be raised enough - maybe there is a resistor in series with the trimpot (and minimal voltage is set by resistor value).


Fascinating stuff, Tremol. I’m really enjoying learning everything I can. This will be duly noted


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## cdwillis (Nov 24, 2022)

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.


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## geoffrey (Nov 24, 2022)

cdwillis said:


> 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


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## geoffrey (Nov 24, 2022)

cdwillis said:


> 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.


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## geoffrey (Nov 30, 2022)

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


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## giovanni (Nov 30, 2022)

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.


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## temol (Dec 1, 2022)

geoffrey said:


> 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.


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## geoffrey (Dec 1, 2022)

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!


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## kristopher (Dec 1, 2022)

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.


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## temol (Dec 2, 2022)

geoffrey said:


> 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.






geoffrey said:


> 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)?






geoffrey said:


> 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.


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## geoffrey (Dec 7, 2022)

kristopher said:


> 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!


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## geoffrey (Dec 7, 2022)

temol said:


> 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
> 
> 
> ...


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.


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## fig (Dec 7, 2022)

geoffrey said:


> 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!


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## geoffrey (Dec 7, 2022)

fig said:


> 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


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## fig (Dec 7, 2022)

geoffrey said:


> 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/


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## Chuck D. Bones (Dec 20, 2022)

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.


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## geoffrey (Dec 21, 2022)

Chuck D. Bones said:


> Thanks, Fig.
> 
> More recommended reading:
> 
> ...


Thanks, Chuck!


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