DIY Dod 250

[geezer15]

Hi I have tried to build a Dod 250. At the moment it doesn't work. Now I have noticed that the Schematic, below has a 1m5 resistor, R1 and a 10uF electrolytic cap, C1 that isn't on the vero layout, 2nd link below. Are these componants necessary for the circuit to work or are they just slighty different variatons of the pedal? Both claim to be the grey version. I have seen at least one other vero layout so I'm not sure I'm using the 'best' one.

http://www.generalguitargadgets.com/pdf/ggg_dist_g250_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_77_grey_dod_od_250/ulysses_77_grey_dod_od_250_1_0.gif.html

Thanks in anticipation
Pete

[CynicalMan]

Neither component is absolutely necessary, but they're good to include. R1 is a pull down resistor that discharges C2. Its only purpose is to stop popping when the bypass switch is hit. I don't think the original 250 had it, but it shouldn't hurt. C1 is a filter cap for the bias voltage. It makes the bias voltage independent of the op amp's bias current. IIRC, 1977 250s didn't have the cap, but later versions did. So, you can safely include or omit these components based on authenticity or functionality, your choice.

[geezer15]

Thanks for your quick response. I will add both componants and continue my search for the fault.
Pete

[pinkjimiphoton]

check, and double check your soldering...not only for inadvertant bridges, but for bad solder joints in particular...they can lay your project low,  bro...sometimes even if it looks good, it'll be screwy inside. keep your tip clean and tinned, and don't be afraid to re-heat connections and add a smidgen of fresh solder. can make all the difference in the world!

and remember to use a roach clip or something as a heat sink on transistors, diodes, and ic's...i have learned the hard way what too much heat can do!

good luck mate!
peace!

[geezer15]

Thanks for the tip. Double and triple checkingsolder joints now now 

[pinkjimiphoton]

my pleasure, hope it helps, mate...i discovered that the joints on some earlier builds had failed, after them working fine for in some cases years...a little hot solder, and they're back in the saddle again!!



rock on, and post pics and clips when ya get it sorted out!! i've been thinking about building one, too!

peace!

[geezer15]

If I ever get it working I will.
I get sound to pin 3 but only a bit of static from pin 6. Pin 4 goes to ground OK and  pin 7 goes to the battery ok. Pin 2 connects to R5 and C3 ok.

R3, both pots both jacks, d1, d2 and c5 all have terminals connected to ground so I am stumped.

the voltage readings pin 1 =0 NC
                              pin 2 = 1.12v
                              pin 3= 0v
                              pin 4=0v
                              pin 5 = 0v NC
                              pin 6= 1.92v
                              pin 7= 7.89v           
                              pin 8= 0 NC

[pinkjimiphoton]

geez,  can ya post the layout you're looking at specifically?

[petemoore]

pin 1 =0 NC
                              pin 2 = 1.12v
                              pin 3= 0v
                              pin 4=0v
                              pin 5 = 0v NC
                              pin 6= 1.92v
                              pin 7= 7.89v        battery is 'ok-ish   
                              pin 8= 0 NC
  The voltage divider should have 2x = value resistors strung from
Gnd. to V+, where they're connected should be in the middle of the power suppy: @9vdc supply, ~4.5vdc should be read at the divider node.
  This node has a large resistor which pulls the relevant opamp pin to 4.5v bias, the other two [the other input pin and the output pin] should follow suit, and the +/- input pins will be 'center-ish between the two power rails, allowing room for the signal to swing +/- for a ways before hitting a power rail.
  What is the voltage reading at the divider ?
  Suspect the inputs could be connected to ground since they are all at a common voltage potential [o.ov], a short of the AC signal path to a DC reference will shunt ~everything AC to ground.
 

[geezer15]

pinkjimiphoton
thanks
the layout is in my first link at the top the grey dod 250 on vero. I was comparing it to the schem in the other link i posted with it. The only changes I made were to add the R1 1m5 (actually a 1m) and the C1 10uf  electrolytic cap I was originally asking about shown on the schem. I've added them again here

http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_77_grey_dod_od_250/ulysses_77_grey_dod_od_250_1_0.gif.html
http://www.generalguitargadgets.com/pdf/ggg_dist_g250_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a';

[geezer15]

petemoore,

I am getting 3.95v at the node thats where R4 and R3 join on the vero layout. I have just noticed the Schem shows a resistor of 470k (R4) but the vero has a 1m resistor (R2). It is the vero Im following so thats what i've put in but I'm not sure its correct?.

[geezer15]

pin 3 is the one i guess your saying should be at about 4.5v it is def at 0. It is not shorted to ground. Neither are C1 or R1 (going by the vero componant labeling here).

[geezer15]

GOT IT!.

Thanks you were right! I had 4v at the node so I had to have a bad connection not to get 4v at pin 3 right. It was the connection to R2. Looked a perfect solder joint but re did it to make sure several steps ago but I guess the leg wasn't far enough in the board. Gave it a shove in and I've got 4v at pin 3.

The circuit works.

I have built a. MXR Dist + and plan to put the 2 circuits together in one housing so I can just switch between them.

Thanks for all your time and effort.

If I keep making silly mistakes I may learn enough, one day, to help others. Lets face it if it had worked first time and would never have known why.

Pete

[geezer15]

I don't understand how the resistor came disconnected. I mean I put the lead through the hole soldered it and then trimmed it. It can only have become disconnected later, perhaps when I was reheating all the connections.
Another thing I found, earlier, was that  the input jack was shorting out. It was definately OK when I first wired it because I tested the two tabs to see which was which, so it became faulty later. Also when I checked the vero strips for shorts with my DMM it didn't show up as shorting out, thny a little while later it is shorting. So I don't know it just wasn't meant to be an easy build.

[Renegadrian]

ahhhh the 250, one of my favs!!! I really like it! And it's quite an easy build! Congrats on getting over trouble and please post pics when boxed up!!!

[aranubanti]

Hmm, I'm having similar problems with my build. I used Renegadrian's layout and Neoclassic schem:

http://home.comcast.net/~snmavronis/neoclassic741sch9.jpg

Currently I get no sound, but the pedal comes on. Voltage readings are:

Pin 1: 0 V
Pin 2: 0 V
Pin 3: 6.18 V
Pin 4: 0 V
Pin 5: 0 V
Pin 6: 8.47 V
Pin 7: 9.11 V
Pin 8: 0 V

The 6.18 V on the pin 3 sound a bit off... Also wondering about the pin 6 voltage :/

There's not even any hiss coming thru. I added a true bypass according to this link:

http://www.little-black-box.co.uk/images/uploads/wiring-diagrams/3pdt-wiring.jpg

Any advices?

[Renegadrian]

Are you using THIS layout?! I don't have one 250 handy atm, but yeah pin 3 is definitely way out of voltage! 9V go thru 100r, then a voltage divider (the 2 22k) and then 470k to pin 3. you should get around 4v but yeah can't make any readings on a true pedal.
I'd check that first. then, try to wire direct input and output, as the fx is always on, and see what happens...if that works it's the wiring of the switch.

[Steve Mavronis]

Hmm, I'm having similar problems with my build. I used Renegadrian's layout and Neoclassic schem:

There's not even any hiss coming thru. I added a true bypass according to this link:
http://www.little-black-box.co.uk/images/uploads/wiring-diagrams/3pdt-wiring.jpg

My NC schematic already included a non-pop true bypass wiring for the 3PDT. Is your alternate 3PDT true bypass wiring and output jack and/or footswitch signal wire connected correctly to the PCB? They are completely different from each other how they connect so you might have something confused between the two wiring schemes.

[aranubanti]

Are you using THIS layout?! I don't have one 250 handy atm, but yeah pin 3 is definitely way out of voltage! 9V go thru 100r, then a voltage divider (the 2 22k) and then 470k to pin 3. you should get around 4v but yeah can't make any readings on a true pedal.
I'd check that first. then, try to wire direct input and output, as the fx is always on, and see what happens...if that works it's the wiring of the switch.

Indeed that's the layout.

Gotta try that as soon as I get home again..

[aranubanti]

Hmm, I'm having similar problems with my build. I used Renegadrian's layout and Neoclassic schem:

There's not even any hiss coming thru. I added a true bypass according to this link:
http://www.little-black-box.co.uk/images/uploads/wiring-diagrams/3pdt-wiring.jpg

My NC schematic already included a non-pop true bypass wiring for the 3PDT. Is your alternate 3PDT true bypass wiring and output jack and/or footswitch signal wire connected correctly to the PCB? They are completely different from each other how they connect so you might have something confused between the two wiring schemes.

Oh, didn't even realize yours was different.. It's strange because I've used the wiring in the link I provided before in my Tubescreamer build and it has worked perfectly. I compared the two side to side and theyre identical. So maybe the vero- board sucks... I get 9.11 V at the voltage divider junction, that's way off. Gotta check the connection... But you'd think it wouldn't deafen the pedal, only change the sound? So perhaps there's an error in my board.