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It's not as silly of a mistake as troubleshooting a pedal for 30 minutes until realizing you forgot to put the transistors in. Nope, that's never happened to me at all...

Or you don't power it. Or put in any ICs. Or plug in a guitar.

diablochris your answer made me laugh so hard, you should put it in your signature! And I've actually made all of the above, especially the IC one!

Regarding the topic, yes it was missing the Gate resistor, (shame on me!) so you can consider this one closed!

Thank you all for the answer and the laughs!

The gate needs a reference voltage, which in this use is typically a connection to ground. You need another resistor to ground from the gate - large value like 2.2m.


Alternatively, you can just take out C1 and replace it with a jumper.

Thanks for answering!
Could I've been so stupid to miss it?
I'll check the original schematic and the board.

Have any pictures? Could you fit it on the side or top of the enclosure?

Alternatively, use a trimmer and one of the little trimmer turners shaft things like on some of zvex pedals. I can't recall the name, but you basically install the trimmer inside, white a hole drilled on top, then this little shaft fits in through the hole and mounts into the trimmer + shape. Hopefully there's someone out there that has a source for these, and prove that I haven't totally lost my mind/this exists.

They should be the ACP trimmers with their axle, like these:
https://www.musikding.de/CA9V_1

Hi guys!
Hope you're havenig a nice weekend.

I'm working on a new pedal and I've designed a very simple stage with a J201 in a SOT23 package.
As you can see in the schematic it's pretty straightforward and it sounds very good, when it's working 
buffer1.png

It worked on the breadboard and I've ordered some PCBs from a factory, made with eagle and tested so I'm pretty sure about the board quality.

The thing is: when I connect everything and plug my guitar or a signal generator I got nothing on the speaker or the oscilloscope. While checking the connections I thouched the tranny and it started working. Disconnected and connected again and it kept working. Disconnected for a while this time and connected again, not working. So I touched the transistor again and magic! It works!

I've resoldered it again, double-checked connection but nothing, it always needed the finger magic to start doing is job. So I tried to look closer while I was touching it and discovered that what my finger was doing was connecting the D and G pin of the J201. So I tried with a piece of wire and yes, finger magic was now wire-magic. The weird thing is that I dont need to keep touching it, just a brief connection of less than a second.

Guys can you explain to me what was happening and why the J201 need that to start working? After that brief connection with the finger or the wire it goes on without any trouble at all.

As Paul from GIYGuitarPedals is taking care of his family (Family First mate, best of luck to you and your son) I'm asking here for some assistance.

I bought Paul's 7min Fuzz and I want to incorporate it into a combination pedal that's running off of 12 volts.
It's a 12au7 Tube boost & distortion pedal that requires 12v.

7min Fuzz Schematic http://www.diyguitarpedals.com.au/shop/boms/7_Min_Fuzz_Schematic.pdf

So I roughly calculated that for the 7min Fuzz to work on 12v I need to increase the voltage of R1 (10k Ohm) to a 12k or 13k ohm resistor?
Can someone with better electronics knowledge confirm this please?

Also I only have a 50k Ohm Audio pot will this be ok for the Volume control?
His circuit requires a 100k Ohm Audio pot.

50k Ohm is fine for the volume pot.
For the tranny, consider that here is poorly biased on purpouse to achieve the fuzzy tone so I THINK you can leave it that way or better subs it with a trimmer to find your "spot". Consider a breadboard too, it's the fun part

You have to swap battery and positive voltage wires on the DC jack I think. Look at the link:
http://1.bp.blogspot.com/-oNCRd1OXiV8/VX1VE3EG-wI/AAAAAAAAFPA/0fH31CwE64E/s1600/just-dc-jack-03.jpg

you have to solder the wire from the battery to pin 3: it's going to be disconnected as soon as you insert the dc plug.

The others are correct: when you insert the In jack it will short Ring and Sleeve connecting the wire from the DC jack to GND, this way the pedal is active only when the input jack is connected.

If you dont plan onusing battery you can obv. discard this part

Just to elaborate a bit on Jon's excellent post - re-biasing depends partially on whether or not you are coupling different stages with a cap. When not coupling, DC offset might play a factor esp. when going between two different IC types. But it really depends on how it's being done. At the same time, there is a lot of forgiveness in pedal designs so sometimes you can get away with things an engineer would frown upon.

Thanks for answering!

Yep I realized that if the first bias is setting a reference point from which the IC Output can swing up and down so if connected directly to the second I shouldn't need to bias again. If I put a cap in there I have to re-bias.

Regarding DC offset I think that going from a biased buffer stage to a gain stage on the same IC shouldn't be really a problem.
But DC offset and what may cause it is something I'm learning recently (I've recently decided to understand things before building it so I can possibly debug them), and the only thing I to prevent DC offset right now is that's almost mandatory to use a cap to GND on the voltage divider that provides the bias current 

Breadboard a dual op amp. Bias the first op amp and run a piece of wire from pin 1 to pin 5. What's the voltage on pin 5?

Now bias pin 5 separately. What's the voltage on pin 5?

If there is a difference, what effect do think that difference might have?

What effects does putting a capacitor in the signal path have? Jot a few of them down (whatever you can think of) and check the wikipedia capacitor article to see if you missed a few. Are they good or bad effects? Under what circumstances might a "good" one be bad?

What situations would you NOT be able to do the first method? Hint: Look at the input of any simple op-amp based pedal (a buffer is simplest). Breadboard the extra components and measure voltages everywhere if you need to.

Possibly the best answer I could ever get!
I was missing two points here: one about biasing and one about empirically searching and discover on my own!

Hi all guys!
I have a little doubt! When using an op-amp (TL072) I usually bias the input on the first half (a fixed gain stage for example, or a buffer) and when from the first output the signal goes to the second half I bias it again.
I've checked many schematics and sometimes it's done this way and sometimes not. On my last build I didnt bias the second input, and not even used a cap between the two halves (buffer and gain stage) and it worked good.
Is there any pros or cons to do it one way or another?
thanks all!