SOLVED .Chop shop biasing and sag pot...

[The Gator]

I want to make sure I understand the biasing method for this new version of the chop shop circuit.
The sag pot turned all the way CCW (should make it lowest resistance reading) then measure from the provided pad on top of the trimmers. Measure from the pad to ground I assume. Fine tune each trimmer until 6 to 6.6v is achieved?

I did this and the pedal works. However turning up the sag pot just cuts the sound out rather quickly. It was also very, very touchy to tune in the trimmers. It goes from .4V to 7.4V when I barely touch the trimmer.
It gets extremely loud, but not much drive.

I need to make it clear that I used some 2N5458 jfets in place of the J201 jfets.
I also used a TO-92 package 2N2222 instead of the TO-18 metal can type. I was careful to examine the pinout. The hfe on this 2n2222 tested out at 410. Little higher than the metal can spec, but not much.

 

[The Gator]

I did it again...(looks down in shame)
Here are some pics...

 

[The Gator]

After finding the most important thread on the chop shop there is, I tested the all of the n-channel jfets I had. The Idss measurements tested were between 1100uA and 1600uA. A lot more than recommended. I might have to find a place to get some more, that test better than that.

 

[MichaelW]

After finding the most important thread on the chop shop there is, I tested the all of the n-channel jfets I had. The Idss measurements tested were between 1100uA and 1600uA. A lot more than recommended. I might have to find a place to get some more, that test better than that.

Hey @The Gator. DM me your address, I can send you some MMBFJ201's to try.

 

[Laundryroom David]

Hey @The Gator. DM me your address, I can send you some MMBFJ201's to try.

MMBFJ201 def the way to go. I picked 2 at random, didn't test, plugged 'em into the sockets and everything biased right to 6.6v with no problems. Hopefully you'll have a similarly charmed experience with them!!

 

[The Gator]

Just PM'ed you.
Thank you

 

[Chuck D. Bones]

I need to make it clear that I used some 2N5458 jfets in place of the J201 jfets.

2N5458 is not a good sub for J201.
The 2N5458's Idss and Vp are much higher than J201 and are way too high for the Chop Shop.

 

[The Gator]

Thank you Chuck.
Yes I know first hand now that they are not a good sub for J201 lol. It's all I had laying around.
I saw your post on Jfet testing. Jfets are still a mystery to me for sure. I need to get my head wrapped around understanding what specs are important for our purpose, and as you said, more importantly what does circuit need.
That is why I am here. This is a very smart and helpful community. I like to learn. I could just go out and buy a lot of these pedals, but I really want to learn and understand more about audio circuits.
There is much for me to learn lol

Thanks for your help guys

Gator

 

[Chuck D. Bones]

I wrote some articles on JFETs in Chucks Boneyard, you might find those informative.

 

[LukeFRC]

This post was really useful in giving the LDSS for each jfet to aim for.
I bought 10 from here, tested them all and used the two for closest to the middle of the recommended

Post in thread 'Chop Shop gain not working'
https://forum.pedalpcb.com/threads/chop-shop-gain-not-working.5186/post-47046

 

[The Gator]

Thank you to everyone for the help! Especially the very kind and generous MichaelW!
Michael sent me a strip of j201 jfets along with some adapter boards and a proper TO-18 can 2N2222A.
Among other things actually. I am super grateful!
I was not enthused about desoldering the old ones and bending the sag pot out of the way.
So when I went to microcenter to get some wire leads and a smaller soldering tip for the hakko fx888, i saw a hakko fr301-3 desoldering iron. They wanted way too much for it. But they price matched with Amazon and I paid $249.
What an awesome tool! So easy!
So I desoldered and then did up the tiny little j201s on the adapters (wow they are tiny!) Then socketed the new 2n2222A.
Oh buddy...it biased easily and now the pedal sounds fantastic!
Absolutely wonderful to be here in this community! Thank you!
Thanks Michael!