SOLVED Having trouble calibrating the Chop Shop!

innerlight

innerlight

Active member
PREAMBLE/RAMBLE:
Hello everyone!
Let me start by saying I HATE JFETs. If I build a pedal and it has a frustrating problem you can bet it has a JFET.

Rant over!!

That aside, I just built a Chop Shop after much recommendation from the forum. I've read all the tutorial posts from people talking through the calibration process.
The pedal is passing signal, and it seems like its all good to go except the calibration.
The JFETs are SMT bought from pedal PCB. I didnt know how to pre test their values so i chose two at random. I figured it has the trimmer pots so I can get them in the range right?

THE CONFUSING PROBLEM:
I calibrated Q1 and Q2 to within 6-6.6V as recommended, no problem there (photos included for each). With sag pot on minimum (full CCW), volume and gain maxed.

Pedal sounds fine (really good even) on that setting. HOWEVER as i increase the sag pot, wild squealing happens akin to a gated fuzz or feedback. I used a 2N222A transistor and it is inserted with the orientation matching the silk screen, is this correct? I tested all resistors before soldering so I know theyre ok.
Can someone please advise? I am officially lost. Seems like my build is fine and the problem lies in the JFETS. Should I de-solder those and try some other ones?
Any advice greatly appreciated :cry:
 
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Small update:
When calibrated at these values, the wild squealing only happens when drive and vol are maxed and I sweep through the sag pot. It actually sounds fine when I back off volume. Is this typical behavior?
 
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innerlight said:
Small update:
When calibrated at these values, the wild squealing only happens when drive and vol are maxed and I sweep through the sag pot. It actually sounds fine when I back off volume. Is this typical behavior?
Click to expand...
I’ll have to check with mine (which will likely have to wait until tomorrow) but it wouldn’t be the first time I’ve had a pedal do this onlt on max settings. My blue Steele (blues driver clone) does this if you max all controls also j201.
 
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Locrian99 said:
I’ll have to check with mine (which will likely have to wait until tomorrow) but it wouldn’t be the first time I’ve had a pedal do this onlt on max settings. My blue Steele (blues driver clone) does this if you max all controls also j201.
Click to expand...
Thanks so much! I appreciate it. It sounds great otherwise! Hoping this is normal behavior. Also wondering if a lower value volume or gain pot might fix the issue. Either way I guess I’d never max both out, but having unusable settings tends to gnaw at my subconscious!
 
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PJS said:
Not an expert on this, but Google says that 2n2222a is a bit higher gain than 2n2222. I am guessing that could mean potentially that a 2n2222a could send the whole lot over the top at really high settings?
Click to expand...
That's interesting! I do have some 2N2222's coming in the mail. Can anyone confirm this?
 
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I own a Gen 2 Barbershop, and IIRC at no settings does it squeal — we build clones of pedals, so they should perform as per the originals.

Maybe desolder the SMD and resolder a bunch of JFETs on daughterboards so you can socket them in there for auditioning.

Hope you're able to sort it out, it is a great-sounding circuit.
 
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Feral Feline said:
I own a Gen 2 Barbershop, and IIRC at no settings does it squeal — we build clones of pedals, so they should perform as per the originals.

Maybe desolder the SMD and resolder a bunch of JFETs on daughterboards so you can socket them in there for auditioning.

Hope you're able to sort it out, it is a great-sounding circuit.
Click to expand...
Great idea, I was going to get daughter boards but could not find somewhere that had them in stock! Does anyone have any leads there?
 
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Feral Feline said:
I own a Gen 2 Barbershop, and IIRC at no settings does it squeal — we build clones of pedals, so they should perform as per the originals.

Maybe desolder the SMD and resolder a bunch of JFETs on daughterboards so you can socket them in there for auditioning.

Hope you're able to sort it out, it is a great-sounding circuit.
Click to expand...
Also I’m wondering if the JFETs are biased correctly, could they be the problem? If a JFET will bias, and is within range then does that mean it’s doing it’s job?
 
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I soldered the JFETs to my Low Tide's board, wish I'd used adapters. I probably even had some adapters at the time.

I build it just before moving, it didn't work, it got packed and disappeared — finally came across it recently while looking through old moving boxes of other storage stuff... let the trouble-shooting commence! Hope I don't have to desolder resolder those SMD JFETs...

Anyways, just sayin this :poop: happens... sometimes it even hits the fan, woe be yee if it's the ceiling fan...
 
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Feral Feline said:
I soldered the JFETs to my Low Tide's board, wish I'd used adapters. I probably even had some adapters at the time.

I build it just before moving, it didn't work, it got packed and disappeared — finally came across it recently while looking through old moving boxes of other storage stuff... let the trouble-shooting commence! Hope I don't have to desolder resolder those SMD JFETs...

Anyways, just sayin this :poop: happens... sometimes it even hits the fan, woe be yee if it's the ceiling fan...
Click to expand...
I hope very soon we both have working chop shops
 
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I meant to check this yesterday but the day got away from me sorry. Maxxed gain/volume no squeal in my build. Although I feel like 25% of my sag pot is actually usable, (I didn’t put the sag pot on my bread board build). I am using a to-18 2n2222a hfe is 205 (which is lower than all the to-92 2222a’s I have which are 250-300).
 
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Locrian99 said:
I meant to check this yesterday but the day got away from me sorry. Maxxed gain/volume no squeal in my build. Although I feel like 25% of my sag pot is actually usable, (I didn’t put the sag pot on my bread board build). I am using a to-18 2n2222a hfe is 205 (which is lower than all the to-92 2222a’s I have which are 250-300).
Click to expand...
This is so useful! I’ll try switching out this 2N2222a with another and see what happens there. I have some legit 2N2222s coming so that might help too. I’ll report back. Many many thanks for your generous help
 
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