adding pots (drive and vol) to Davisson Easy Drive

[fuzzy645]

Assuming the #'s 1, 2 and 3 for pot lugs (as per diagram above),

...then, if we look at this info about the Davisson Easy Drive here:
http://www.diystompboxes.com/analogalchemy/sch/easydrive.html

2 statements are made that I am trying to understand where and how to connect (and to which lugs)

1.  If desired, a 1k linear pot may be used in place of the 680-ohm resistor, with the 22uF capacitor attached to the wiper. This makes a good gain control.

Since the 680 ohm and 22 uf cap are originally in parallel I'm trying to figure out how to sub in the 1K pot.    Would the lead from the transistor's emitter go to lug 1, and then the 22 uf cap to ground?  I'm just not sure how to integrate this pot.


2. A 100k volume control may also be added from the .1uF to ground, with the output taken from the wiper.

So would that be .1 uf into an outer lug (either 1 or 3) and then the final output wire goes to the center lug.

Schematic is below for reference.

Thanks

[Davelectro]

You wire those pots just like in a fuzz face.

For both controls, Lug 1 is the one that goes to ground.

[fuzzy645]

You wire those pots just like in a fuzz face.

For both controls, Lug 1 is the one that goes to ground.

Thank you.

So it would be like the volume and fuzz in this:

[Davelectro]

Yes. But make sure your 22uF electrolytic has its negative side connected to ground.

[fuzzy645]

Yes. But make sure your 22uF electrolytic has its negative side connected to ground.

Its funny how you said that  

I just tested my circuit and I was getting sound but no fuzz.  I then took a closer look and I noticed that I hooked up the electrolytic cap backwards (positive to ground  ).  I then promptly reversed that cap, but unfortunately now I get no sound at all.   Would it be safe to assume that I completely fried the transistor by my  major NOOB mistake?  If so, I assume I can just swap out the transistor for another....or did I also fry other components by that boo boo (like the 2 diodes)?  Thoughts??

[Davelectro]

You can't fry a transistor that way. You might have killed the electro, though.

[Earthscum]

Another pot to add to this is in the diode/cap feedback string. I'd say go between the collector and .1u cap and try out a 1k pot there to soften the distortion. Just wire it so when you have it all the way left, you have the full 1k, and all the way to the right is 0 Ohms. I think I found that 2k would be best for range, and 5k maybe didn't do too much? It's been awhile. It's a fun circuit to play with.

BTW, diodes and transistor should be fine... like Dave said, it's probably your electro. Check your voltages, always. When I set up anything now, I start stage by stage and make sure the collectors/emitters are about the voltages I'd expect them to be. Should be about 4.5V, give or take a volt at worst.

[fuzzy645]

Why does the Fuzz Face diagram have the positive end of the electrolytic cap to ground, where as the Davisson schematic has the opposite?  Is it because of the type of transistor used?

[Davelectro]

Why does the Fuzz Face diagram have the positive end of the electrolytic cap to ground, where as the Davisson schematic has the opposite?  Is it because of the type of transistor used?

Yes. The Fuzz Face you linked above uses PNP transistors and positive ground.

This one is NPN / negative ground, just like the Easy Drive:

[Joe]

http://www.diystompboxes.com/analogalchemy/sch/easyknobs.gif

Been there the whole time, not sure why I didn't have a link to it.

[fuzzy645]

http://www.diystompboxes.com/analogalchemy/sch/easyknobs.gif

Been there the whole time, not sure why I didn't have a link to it.

Thank you all for your help.

Joe - that schematic with the pots in it helped a lot.   

Quick question - given the schematic that you provided, can I readily swap out the 2N5089 transistor for a 2N3904 with no other changes to the circuit in response to that?  The reason I ask is I have seen some variations on this schematic.   

Then, if the answer to my question is yes, I wonder if it would be possible (or worth it) to use a 3PDT switch to swap transistors on the fly (between the 2N5089 and the 2N3904)??

Thanks again!!

[Joe]

You can use any NPN transistor, the 2N5089 has higher gain/lower noise compared to the 2N3904. Can use germaniums, darlingtons, etc.