Hi
it's used in a circuit to "push up" a CD4017, so I think the subst must be as close as possile to the original 2N222. I've used a 2n3904, but it seems it doesn't work well.
Also does anybody has a link to a "substituition table" for transistors, fet and stuff like this.
Thx 1G for help
Armando
Not comprehensive but useful nonetheless.
http://www.aronnelson.com/gallery/v/DRAGONFLY-LAYOUTS_0/The-Mod-Zone-_/TRANSISTOR_SUBSTITUTION_CHART.gif.html (http://www.aronnelson.com/gallery/v/DRAGONFLY-LAYOUTS_0/The-Mod-Zone-_/TRANSISTOR_SUBSTITUTION_CHART.gif.html)
http://www.datasheetarchive.com/search.php?t=0&q=2N222&manystr=&sub.x=0&sub.y=0
see the cross reference
2N222 or 2N2222?
Thx to all for links,
R.G. wrong typing it's a 2N2222
Armando
2N2222 is a metal case TO-18. It's much more widely available as a TO-92 plastic case "PN2222", and possibly as MPS2222.
I'm pretty sure you can get 2222s at radio shack, if you have one nearby. If you can measure HFEs, if memory serves the 2222 has slightly lower HFEs than the 3904, which might explain the sound difference. You might be able to test some 3904s and find lower HFE examples for your pedal.
Quote from: R.G. on January 11, 2008, 02:32:13 PM
2N2222 is a metal case TO-18. It's much more widely available as a TO-92 plastic case "PN2222", and possibly as MPS2222.
I was thinking about some I could have available at home ( in my, still too small, trannies fleet!)
Quote from: tcobretti on January 11, 2008, 02:57:33 PM
I'm pretty sure you can get 2222s at radio shack, if you have one nearby. If you can measure HFEs, if memory serves the 2222 has slightly lower HFEs than the 3904, which might explain the sound difference. You might be able to test some 3904s and find lower HFE examples for your pedal.
There's no sound involved in this part of the circuit , only, using a 3904, it doesn't seem to push up the cd4017 ( a decade counter) in the right way. Here's a picture of the part of the circuit involved.
thx
(http://i256.photobucket.com/albums/hh174/arma61/Trigger.jpg)
The 3904 should work fine in that circuit. Or as well as a 2222 anyway. I would
(a) check the pinout on the device you're using
(b) put a 4.7K resistor in series with the base of the transistor after the pushbutton switch.
(c ) Make sure the resistor that pulls the emitter to ground is more than about 10K.
Actually, I would do none of that. I would use a 2N3906 PNP. I'd tie the emitter to +9, the collector to that same RC on the logic input, and I'd use a 10K resistor in series with the base to a pushbutton to ground. Emitter followers are prone to ugly, funny oscillations in setups like this.
Thx R.G. I have to try first solution as the pcb is already made and populated, so hard to modify it, then if that solution is not going to work I'll add a small board with a 2N3906.
Thx to all for help.
Armando
Just cut the trace between the switch and base and solder a 4.7k resistor across the gap on the underside of the board.
Ok an update, only had time today to test R.G. suggestions and, I had no doubts, it works great!, the pushbutton doesn't miss a stroke, everytime I push the button it goes to the next FX and corresponding LED turns on. thx to RG and to all here.
edit: I had 1k from emitter to ground, changed to 15K et voilà the magic!
Quote from: arma61 on January 11, 2008, 08:54:48 AM
Hi
it's used in a circuit to "push up" a CD4017, so I think the subst must be as close as possile to the original 2N222. I've used a 2n3904, but it seems it doesn't work well.
Also does anybody has a link to a "substituition table" for transistors, fet and stuff like this.
Thx 1G for help
Armando
Late to the party I know but this might come in handy down the road.
http://www.ee.washington.edu/circuit_archive/parts/cross.html
Take care
dave