Chop shop quick question

[Atom ant]

Why do bias 1and bias 2 on the chop shop have 5 holes? Most bias pots have 3 legs? Also, what are the metal pads above for?
Will a non 3362p type work?

 

[spi]

It's to accomodate 2 different sizes of bias pots. You can use non-3362p, you can use whatever fits. These kind fit too

https://www.taydaelectronics.com/potentiometer-variable-resistors/trimmers/6mm-top-adjustment/50k-ohm-trimpot-variable-resistor-6mm.html

The pads above are to probe the bias voltage with your meter.

 

[Atom ant]

Can you expand on the probing? I guess i am probing to a specific number instead of to ear? I think I’m in over my head. Sorry, never metered j201s before.

 

[spi]

Turn the sag all the way down, then use the trims to set the voltages to around 6V. That should get you a decent sound. From there you can tune by ear.

Or skip the voltage measurement and go by ear all the way.

 

[jrhevron]

Actually... I have a chop shop question as well: the notes say that you need a PN222A transistor. I'm ordering from smallbear and you need to order a 5 pack. You can order a single PN2925, though. Is that an okay substitute?

 

[jrhevron]

Actually... I have a chop shop question as well: the notes say that you need a PN222A transistor. I'm ordering from smallbear and you need to order a 5 pack. You can order a single PN2925, though. Is that an okay substitute?

Would 2N222A work?

 

[spi]

Would 2N222A work?

a 2n2222a would yes--I think the pinout is reverse of a pn2222 so you might have to insert it opposite--always double check that stuff when subbing parts

 

[jrhevron]

Thank you!

Going to make this for bass. I have an old Plumes build I'm just going to sub it into. I've gone through a bunch of bass OD's lately and feel like this could be what I'm looking for.

 

[jrhevron]

Just ordered my components and of course accidentally just ordered one jfet... doh... seeing if pedalpcb or smallbear still has my order in hand.

 

[jrhevron]

Whew... settled that... but, do you need to match the jfets for the build? Or does biasing achieve that?

 

[andare]

I have another question before I build mine.

The current production model has 4 trim pots



And this is from the FAQ (emphasis mine):

Can I adjust the trim pots in my Barbershop overdrive?

As it says on the Barbershop PCB, adjust nothing. The trim pots were put in the pedal to ease the calibration process, so we recommend not touching anything if you can help it. If you’d like a little more or less drive from the pedal, you have our permission to adjust the gain trim pot, as this is the easiest to set, and the amount of drive one desires is a very personal thing.

So 3 trimpots for the 3 transistors. I guess the 3rd trimpot replaces R5 to set the bias for Q3? That section is basically an LPB-1.
What about the gain trimpot? Where is it in the circuit?

 

[spi]

Unless somebody traces the new circuit we'd just be speculating what the trims do.

Here's my speculation:
I see one called sag--I suspect that one must adjust the range of sag pot.
If there's one that controls the gain (not labeled as such), I suspect it sets the R5.

 

[Robert]

If there's one that controls the gain (not labeled as such), I suspect it sets the R5.

Q3 is an emitter follower, R5 wouldn't affect the gain.

If I'm speculating, I'd guess that it's either fooling with R4 / R7, or adding some series resistance to C3 / C5.

Someone should trace the new circuit.

 

[jrhevron]

Beautiful PCB on the production model.

 

[andare]

Beautiful PCB on the production model.

Better be with them prices haha.

 

[jrhevron]

Whelp... put the transistor in the wrong way and shredded it while trying to take it out.

I have a 2n3904 and a 2n5089 as well as a bunch of muff transistors... would any of those be a decent sub for pn222a?

 

[spi]

Whelp... put the transistor in the wrong way and shredded it while trying to take it out.

I have a 2n3904 and a 2n5089 as well as a bunch of muff transistors... would any of those be a decent sub for pn222a?

yeah, they would work

 

[Harry Klippton]

Someone should trace the new circuit.

Are you saying I have to get a third version of this not having actually built the first two yet? Good grief

 

[Robert]

Are you saying I have to get a third version of this not having actually built the first two yet? Good grief

Are you saying you would?

 

[Harry Klippton]

Are you saying you would?