DIY Dod 250

Steve Mavronis · March 29, 2011, 01:02:28 PM

Yeah I'm just thinking that the board layout you used is okay but the offboard wiring to the rest of the pedal is suspect. Double check that. Anything outside the circled PCB wire attachment pads on my schematic is probably going to be way different than the footswitch wiring pattern that you used. Mine is directly based off this article's diagrams (except I placed the LED resistor on the other side) and it works 100% completely pop-free on several sucessful builds I've done:

gaussmarkov: diy fx
Wiring Up a 1590B
http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b

aranubanti · March 30, 2011, 12:08:35 PM

Well, now I've soldered the switching appointed by you, and still no sound. I do not know why, but the votlage on the voltage divider changed now to 4,51 V. But on pin 3 it's 3,06 V because of the 470K resistor.

I keep coming to the conclusion that there's something wrong in my vero board, because I've checked everything else many times. It's just so uninspiring to try to rip the board off under all those wires..

aranubanti · March 30, 2011, 03:18:51 PM

Hmm, I made an audio probe according to the Geofex site and probed around a little, and the signal stops to the pin 3 of the 741. It's still there at the pin, but not on the pin 6 or 2. So perhaps it is the IC? Hardly believable as I've tried 2 of them already...

aranubanti · March 30, 2011, 04:28:26 PM

Well the problem got solved. It appears that it does matter if I connect the pins 1, 5 & 8. I cut the legs and it works now. Can't wait to test it with my 50 Watter...

Renegadrian · March 30, 2011, 04:57:06 PM

Yeah, I thought you already knew about thoise pins! They are labeled NC (not connected) in my layout! Glad to hear it works, beware it will become one of your favourites too!!!

aranubanti · March 30, 2011, 08:11:37 PM

I feel so stupid now...

Perhaps I should start taking advices literally as they say

There's still the pin 3 voltage problem, I'm getting only 3.07 V there. Before the 470K resistor it's 4.51 V. I suppose the 470K R is in there for a reason though..?

Renegadrian · March 30, 2011, 08:56:04 PM

Why do you call it problem!? I guess it should be that way, see that resistor is there in every schem floating around.
I took my breadboard to see if the voltage is right.
Vin 9.64
Vdiv 4.84 (with 2 22k res)
V after the 470k 3.28

assuming that your supply gives out a little less than mine (unregulated) the 3.07 reading seems a regular value...

aranubanti · March 31, 2011, 05:24:41 AM

I'm a bit of a beginner with IC's

It's just that I've understood from everybodys posts when they say that the "voltage divider halves the DC voltage for pin 3, so it should be 4.5 V" that it really should be 4.5 V

But that clears it out, thanks a lot!

petemoore · April 01, 2011, 02:07:06 AM

There's still the pin 3 voltage problem, I'm getting only 3.07 V there. Before the 470K resistor it's 4.51 V.
Must be the offset voltage of 741 ?
4.5v bias would be ok for pin 3, it'd have more centered bias and so the output would be a more symmetrical swing also.
That'd be nice if symmetric, clean output was desired.
The idea of the 250/D+ is so that the opamp output And the diodes both contribute to distortion.
The input has only to wiggle by some small amount that 3v seems to cover, the output swing is clamped at whatever the diode threshold voltages are for the back to back diodes clip the + and - at each diode [or diodes] foreward threshold voltage.

davepedals · April 02, 2011, 04:09:10 AM

Renegadrian,

looking at your vero layout, i can't figure out how to wire the pots.
what type and value pots do i use?
can you provide a more details for wiring the pots.
How about the diodes - 1n4148? Will 1n4001 work ok?
thanks.

Renegadrian · April 02, 2011, 04:44:41 AM

Dave, you're right about that, I didn't write everything, maybe I'll update that layout. I made it using MarkM PCB layout as reference, so you can just take values from there.
anyway, VOLUME is A100K and DRIVE is B500K. diodes are 4148 yeah.
I only wrote about pins 3 of the pots. DRIVE 2+1 go to ground as VOLUME 1, and VOLUME 2 is out.
I never used 4001 as clipping diodes, but I know they can be an easy replacement, so yeah they will work, dunno the difference in sound...hope that helps!

davepedals · April 02, 2011, 05:23:15 AM

yeah - helps a bunch man, thanks! can i bug you for one more question? What diodes are used in your layout of the Boutique NPN OD?

Renegadrian · April 02, 2011, 08:59:56 AM

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=3056&g2_serialNumber=2
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=3071&g2_serialNumber=4

which basically is YAE (yet another Electra) - http://www.forrestwhitesides.com/files/up/img/layouts/electra_sch.jpg
or his derivatives Trotsky and lovepedal woodrow, and yes my version, Electradrian.

geezer15 · April 02, 2011, 06:20:47 PM

Still not finished-almost there but here is what it will look like.

http://s1228.photobucket.com/albums/ee448/geezer15/?action=view&current=IMG_8465.jpg&newest=1

Shame you can still see the edges of the decal paper transfers! I don't have any knobs to fit yet. Can you believe the 20 odd I have are all the same size- too smal.

http://s1228.photobucket.com/albums/ee448/geezer15/?action=view&current=IMG_8464.jpg&newest=1

The circuits are still wired as they were when tested so I need to remove all the jacks, pots battery clips etc and wire into the housing.

I followed the vero layouts except I didnt use a tantalum 1uf cap in the dist + just a metal film cap. It was physically large but fits ok and its what I had to hand. I don't know if it makes any difference to the sound. I like it anyway. I have used a A100k and have a C1m in the housing at the mo. Waiting for a C500K to arrive

davepedals · April 02, 2011, 10:22:45 PM

thanks man, i have all of these parts so i guess it is next up!

Gordo · April 04, 2011, 02:32:11 PM

Deleted

geezer15 · April 13, 2011, 05:53:07 AM

the C500K arrived and I've wired it all up and its working.
Just 2 minor issues. The pedal is noisy at volume. The two circuits are quite different in volume The Dist + is louder and brighter so I cannot just switch between the 2 circuits as the tone and volume controls need resetting. So leason learned -Next time I build 2 circuits in one housing I will put in separate tone and volume controls. I don't suppose I will want to just switch between the circuits so its, hopefully, not a big deal just thought I'd mention it in case anyone else is thinking of putting 2 pedals in one housing on the 'cheap'.

Joe Hart · April 13, 2011, 08:13:46 PM

You could wire a resistor in series with one of the outputs to bring that volume down a bit so they match better.
-Joe Hart

geezer15 · April 14, 2011, 03:33:50 PM

Thanks, yes I'll look into that.

Evan H · November 23, 2011, 02:34:26 AM

I know I'm reopening an old thread (and on a first post...

) but I just wanted to acknowledge that this thread saved me many hours of frustration. In retrospect it makes perfect sense that NC on the schematic would equate cutting the unused pins.

I was set to open a new thread, but the search command saved me here. I'm happy to say that I'm now ready to try to box up a DOD 250, or at least move to the next level on this particular build

Thanks to all the comments here and to Renegadrian for posting the schematic for others to follow. I'm learning a lot along the way from everyone here and what I would consider small successes, but really more from the "failures" that just inspire me to learn more. There's an incredible amount of knowledge here, and I guess I just wanted to say thank you as it's helped me immensely. Apologies if I should have started a new thread, but I thought it made sense to post it here. If in the future I should do otherwise please let me know.

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DIY Dod 250