SOLVED Chop shop popping when activated + squealing even in bypass

Ale_jellybelly

Ale_jellybelly

Well-known member
Hi all
First PPCB build, the lovely Chop Shop.
Biased the J201 without problems thanks to the threads in here, sounds great, boxed it up and it pops quite loudly when pushing the 3pdt.
Anything obvious that I'm missing? R1 should be the pull down resistor right? Looks fine to me

IMG_20230523_182631.jpg
 
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Ale_jellybelly said:
Did it, no change unfortunately

Going to try and swap it when I get the chance

My shitty DMM doesn't have a continuity tester but tried it with resistor tester and looks like there is no continuity. I hope to solve the popping with a new 3pdt
But the squealing isn't going away :(
Click to expand...

If the switch is fried it could be shorting out internally in all sorts of weird ways - might be contributing to the squeal? I don't think you'd be able to test continuity the way @music6000 described if you have the PCB attached - I don't know what wiring scheme the ppcb breakout boards use but if you could figure that out you'd be able to test it.

The easiest thing to do before going to the trouble of fully replacing the switch would be to disconnect it, and just wire the IN and OUT on the effect PCB right to the jacks, bypassing the switch all together.
 
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music6000 said:
View attachment 55691

What type 2n2222 did you use?
Note Direction of transistor per part number:

View attachment 55692
Click to expand...
It's a 2N2222A, I think I have put it down with the correct pinout as I remember reading on the forum about the different layouts for the two different transistors
mdc said:
If the switch is fried it could be shorting out internally in all sorts of weird ways - might be contributing to the squeal? I don't think you'd be able to test continuity the way @music6000 described if you have the PCB attached - I don't know what wiring scheme the ppcb breakout boards use but if you could figure that out you'd be able to test it.

The easiest thing to do before going to the trouble of fully replacing the switch would be to disconnect it, and just wire the IN and OUT on the effect PCB right to the jacks, bypassing the switch all together.
Click to expand...
good idea, I'll try this to see if it solves the squealing, if it does I'll replace the switch
mdc said:
Also, you deserve a better DMM! A decent Klein / Uni-T / AstroAI model is like $30 and will let you test a bunch of things.
Click to expand...
Kleins are expensive here I'll definitely buy a better one
 
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I soldered input and output directly on the PCB, but the squealing is still there...
It only happens when either:
SAG is maxed or nearly maxed, and GAIN is past 3,
or GAIN is past 3 and SAG is past 12...
So the culprit of the squealing is not the switch or his wiring...
 
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This is very picky about J201's being within the required IDSS.
Where did you get your J201's ???

From the Builder, Thanks Guillaume - FC :
Let's start by sorting the JFETS. As we saw on the datasheet, J201's can have an Idss value from 200uA to 2mA. That is a huge range. For Q1, you want a J201 that has an Idss from 600-800 uA. For Q2, you want one with Idss about 400-600uA.
So you'll have to see what you have to work with. You might be unlucky and have all J201's with crazy values like 1500uA. In that case, the drain resistors will need to be changed.
 
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mdc said:
Might be out of spec JFETs in that case - what voltages are you seeing on the fet pins?
Click to expand...
I'll take a look when I'm home from work... Do you know what values they should be?
music6000 said:
This is very picky about J201's being within the required IDSS.
Where did you get your J201's ???

From the Builder, Thanks Guillaume - FC :
Let's start by sorting the JFETS. As we saw on the datasheet, J201's can have an Idss value from 200uA to 2mA. That is a huge range. For Q1, you want a J201 that has an Idss from 600-800 uA. For Q2, you want one with Idss about 400-600uA.
So you'll have to see what you have to work with. You might be unlucky and have all J201's with crazy values like 1500uA. In that case, the drain resistors will need to be changed.
Click to expand...
I got them in a kit from Musikding... I remember reading another thread here where the pedal squealing was solved by using SMD JFETS, I might have to give it a go with daughter boards.
 
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A quick unscientific test you can do is touch the transistors with your finger to see if that dampens the oscillating that may lead you to the culprit if it is an oscillating transistor

With 2 and 3 joined on the sag pot you'd increase resistance across the pot as you turn it CW have you tried adjusting the trimmers whilst it's squealing

As you'll know fet parameters even from the same lot can vary wildly so might be worth a shot
 
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Had a 2n2222a act similar for me in a fuzzly bear. Was even micophonic at some settings.
Motorboated at extreme setting. Sounded great otherwise.
I doubt its the switch.
Likely the transistor or fet
 
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Mcknib said:
A quick unscientific test you can do is touch the transistors with your finger to see if that dampens the oscillating that may lead you to the culprit if it is an oscillating transistor

With 2 and 3 joined on the sag pot you'd increase resistance across the pot as you turn it CW have you tried adjusting the trimmers whilst it's squealing

As you'll know fet parameters even from the same lot can vary wildly so might be worth a shot
Click to expand...
I finally had time to do some testing, without the switch.
The squealing was definitely affected by the J201s, when moving the trim pots around. I had biased them at around 6v, following advice on here, but that made them squeal. I adjusted the bias at around 6.5v and the squealing has stopped and the pedal still sounds good, maybe a little less gain but it's a low gain OD anyway. So I guess the squealing is solved?
I'll try to solder the switch back and see if it still pops
Man I can't wait to use this one, it sounds so good
 
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Yeah the squealing is solved by rebiasing the JFETs. I think 6.5v is giving me more gain? I might be wrong here but at least the squealing is gone.
I've managed to unsolder the 3pdt board, wired the footswitch directly and it still pops so it's not the board. I guess it's either a faulty footswitch or I don't know.
 
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mdc said:
What is the pedal plugged into? Popping can often be caused by DC leaking out of the input of an amp.
Click to expand...
you know, that could actually be it. Lately my solid state Fender 85 started popping loudly when I turn it off... Tomorrow afternoon I'll try pluggin into my old practice amp.
Damn work getting in the way of troubleshooting.
 
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Ale_jellybelly said:
Hi all
First PPCB build, the lovely Chop Shop.
Biased the J201 without problems thanks to the threads in here, sounds great, boxed it up and it pops quite loudly when pushing the 3pdt.
Anything obvious that I'm missing? R1 should be the pull down resistor right? Looks fine to me

View attachment 49133
Click to expand...

Robert said:
V1 didn't have a pulldown resistor on the output.

It might be worth adding a 10K resistor from the OUT pad to GND.
Click to expand...
do I have the V1 board?
Should I just add a 10K resistor like this:


1697099766450.png

or rather directly on the 3pdt like this:

125B_Wiring_Diagram.png
 
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Ale_jellybelly said:
Looks like this is it. When I play during band rehearsals it is fine, when I'm home it pops so I'm thinking it's my amp
Click to expand...
People smarter than me. If this is the case, is there anything design-wise in a pedal we can do to avoid it? Like are certain designs more or less likely to be affected by this? Or is it 100% the amps fault?
 
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