audio probing a steel string stinger from pedalpcb

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mehfuzhoss
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Post by mehfuzhoss »

I am debugging this pcb. has no effect when footswitch on. bypass signal is fine.

while i am audio probing the circuit. the following happens -

some of resistors carries the audio signal. some of the resistor has dead air/no signal. is this normal! shouldn't all the resistor output the audio signal that is being fed into input? also how about caps! should they output the audio as well? a detailed explanation is appreciated. i am new to effects building. the schematic and pcb board is attached.
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six steel stinger.PNG

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Zokk
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Post by Zokk »

Hi
yes it is normal that not all the resistors are in the audio path.

first you may want to check the power supply voltage in the circuit.
Feed the pedal with a steady signal (sinewave is nice ), then check the signal path with something.
Here your signal path is:
C3 R7 Q2 C6 C8 R12 "GAIN" Q4 C10 "tonestack" R17 "Vol out"
Do you use a simple audio probe (a wire + 100nF capacitor in series), or an oscilloscpe?
a scope is way more convenient to see the problems.

Also check your J201s pinout, it could just be a component placed backwards.

mehfuzhoss
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Post by mehfuzhoss »

j201's have an orientation on the pcb and are installed that way.

what is "Q2, Q4" in the pcb. i don't see these components!

here is a pic of the build

mehfuzhoss
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Post by mehfuzhoss »

I use a simple audio probe with the cap :D

here is the picture of the build.
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plush
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Post by plush »

mehfuzhoss wrote:I use a simple audio probe with the cap :D

here is the picture of the build.
Check your jack wiring
It seems that you've wired your ground incorrectly.

mehfuzhoss
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Post by mehfuzhoss »

the ground is the 2nd from the left (out of the 4 red wires on the bottom close to the footswitch). and it is connected to the center pin of the footsw. and the jack wiring is okay as well.
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plush
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Post by plush »

mehfuzhoss wrote:the ground is the 2nd from the left (out of the 4 red wires on the bottom close to the footswitch). and it is connected to the center pin of the footsw. and the jack wiring is okay as well.

No, I meant this:

Image

mehfuzhoss
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Post by mehfuzhoss »

here is what i find with the audio probe -

C3 signal is okay with 94.6mv
R7 bottom leg has signal with 16.99v , upper leg has no signal with 17.17v
Q2 has no signal with left leg 17.1v, middle 0v, right 17.1v
rest of the signal path has no signal as well.

does this mean that I have a faulty Q2!

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Zokk
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Post by Zokk »

Hi
what is your power supply voltage? it runs at 18VDC?
What is the level of your input signal? you may try with 500mVpp or even 1Vpp.

Have you checked on C6's negative lug?
Can you swap Q2 with another J201?

mehfuzhoss
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Post by mehfuzhoss »

Hello Zokk,

ran at 9vdc.

C6 negative lug has no signal
q2 has 9.21vdc, 8.52 and 9.21 on 3 lugs

i do not have a J201 as spare. I have a 5102.
since q2 has volts showing in the lugs, could it be something else that is at fault?

Thanks for your help on this one.

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Zokk
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Post by Zokk »

Hi
it does not seem normal to me to see +9.21VDC on the gate of Q2.
will need the help of a more skilled person to explain that.

If you have a PF5102, it is more like a J111, a chopper/fast switch. Not sure how it will behave in this circuit.
You may try with 2SK117, 2N5457... N-Channel small signal low noise.

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modman
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Post by modman »

You don't need a probe at this point. You need to check continuity on the board you just soldered to make sure the connections are good.
It takes a somewhat more expensive DMM to have that beep function, but you could make do with a resistance check.

But there is something else going on here too

This layout: with the transistors in a square
Screen Shot 2019-09-25 at 14.34.43.png
Does not match your board: with the transistors on one line
Screen Shot 2019-09-25 at 14.35.06.png
Furthermore, what is OUTPUT in the wrong green layout file above CONNECTS TO NOTHING on the board you populated.
Screen Shot 2019-09-25 at 14.35.34.png
When building your first stompbox, test it without the switch connected, because everybody messes up the switch wiring the first time.
And it's a good thing, because know you will really learn something.

Take the schematic, which component is connected to the output, so where is it on the board etc...
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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