DOD 250, driving me crazy

[FIŠ]

hi guys, I have finished my DOD 250 (gray version) and piece of poop is driving me crazy. Voltages across the pins of a OPamp are normal, all connections to the board are OK (atleast i believe), bypased signal is ok, here is the schematic : http://www.generalguitargadgets.com/pdf/ggg_dist_g250_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
NOTE: changes done to schematics:-  there is no "C3" and "C5"
                                                    - R3 and R2 made 10k ohm, instead of 20 k ohm
                                                    - output cap c7 is 1nF instead of 2,2 nF

here is the sound I'm getting from it : http://vocaroo.com/i/s07zX2vmn03I

note that these "oscilations" do not vary  by them self, it was me messing with volume pot of the pedal throughout the recording, also volume pot on a guitar seems to be doing nothing as well.

this DOD 250 was done on a PCB using photo transfer method, turned out really good and all the leads are in perfect condition, heres the picture of my layout:



please help out as this is VERY depressing for me, lots of time put into planning and realizing...

[tiges_ tendres]

Why do you have your input and output circled that way on the layout? It looks like your input and output are shorting to ground by something you are connecting to them perhaps?

Can you post voltages?

[syntaxera]

please help out as this is VERY depressing for me, lots of time put into planning and realizing...

I am having one of those days as well, so many ups and downs to this thing we do.  Once second you are happy and on top of the world, BUT SUDDENLY...  you hook something else up and something changes.  Then its back to the drawing board, staring at your broken circuit for hours...   very depressing.  Good luck man, I hope you get her working soon.  

[FIŠ]

Why do you have your input and output circled that way on the layout? It looks like your input and output are shorting to ground by something you are connecting to them perhaps?

Can you post voltages?

Circles are not the part of the layout...
Voltages are :  pin2 4,5V, pin3 3,8V, pin7 8,8V, pin6 4,5V (others not connected or ground)

[LaceSensor]

Why do you have your input and output circled that way on the layout? It looks like your input and output are shorting to ground by something you are connecting to them perhaps?

Can you post voltages?

He is just indicating Tip and Sleeve, unless Im really mistaken

[Quackzed]

see if bending the input cap away from r6 does anything to improve the issue  ... maybee something is bleeding  into the input signal...

[FIŠ]

see if bending the input cap away from r6 does anything to improve the issue  ... maybee something is bleeding  into the input signal...

hmm seems t be doing nothing... has anyone encountered similar oscilations?

[chi_boy]

Maybe posting some pictures of the top bottom and wiring would help.  Worth a thousand words as they say.   

[tubelectron]

- Try to reinstall C3 and C5 to see if the oscillation still continues. The capacitor C5 in the FB is important : 27pf is OK. Omitting it can give oscillations. None of my DOD250 uses C3, but it exists on the MXD D+.
- R2 and R3 should not give problems, even if 10K is low (you draw uselessly energy from your battery). I use 220K here and it works perfectly. On the MXR D+, there's 1M.
- C7=1nF is the normal value on the RI "yellow" models.

Here is the schematic of my DOD 250 "Yellow" RI. I have 2 of them. I have built several ones on VeroBoard based on it, with no oscillation problem. note that there is some differences with the "Grey" DOD250.



One of my variant of the DOD250 uses the LM308N, see the schem below. Again, no oscillation here, even when the 308 is directly substitued to a 741.



A+!

[Pyr0]

@ tubelectron.
Interesting subbing the LM308N, how does it sound compared to the original ?

[tubelectron]

@ tubelectron.
Interesting subbing the LM308N, how does it sound compared to the original ?

Well, something between a DOD 250 and a RAT... I would suggest at first to stick with the original 4K7 and 56n in the gain control, instead of 470 and 68n, and compare. I returned to these values and reinstalled a 741, without taking the time for a trial with the 308N with these original values. The 470 + 68n gave more gain and bite than the 4K7 + 56n, but the sound lost its fatness. I should reinstall the 308 to see how it behaves with 4K7 + 56n !

A+!

[FIŠ]

@tubelectron

thx for the info! will try adding C5 and see if it will remove oscillations, ill take a snapshot of my board later

[FIŠ]

some pictures of my work:





soldering looks messy cuz of uncleaned flux, it is neat and tidy in reality and all the joints are shiny so cold solder joint possibility is minimal

[tubelectron]

@tubelectron
thx for the info! will try adding C5 and see if it will remove oscillations, ill take a snapshot of my board later

So is there any improvement doing that ?

soldering looks messy cuz of uncleaned flux, it is neat and tidy in reality and all the joints are shiny so cold solder joint possibility is minimal

Well, examine it with a magnifier : who knows ?

I see 4 green wires in a heatshrink : why ? Do you really need a heatshrink ? Try separating these wires : they may be a source of unwanted coulping (I doubt, but who knows ?)

For info, I finished late evening another DOD250 variant : single knob (volume) + 2 footswitchable distortion preset (blues/rock) with balanced volume : it bugs. No signal out. That's the norm, even after circa on hundred pedals made : I barely made pedals working at the 1st time... The preliminary checking that I have done did not revealed the fault (a "big-joke-style" bug), so I will do some signal-tracing this afternoon, and supsect everything... As usual !

A+!

[ZeusMalt]

Something funny around the diodes in the last pic?

[FIŠ]

@tubelectron
thx for the info! will try adding C5 and see if it will remove oscillations, ill take a snapshot of my board later

So is there any improvement doing that ?

soldering looks messy cuz of uncleaned flux, it is neat and tidy in reality and all the joints are shiny so cold solder joint possibility is minimal

Well, examine it with a magnifier : who knows ?

I see 4 green wires in a heatshrink : why ? Do you really need a heatshrink ? Try separating these wires : they may be a source of unwanted coulping (I doubt, but who knows ?)

For info, I finished late evening another DOD250 variant : single knob (volume) + 2 footswitchable distortion preset (blues/rock) with balanced volume : it bugs. No signal out. That's the norm, even after circa on hundred pedals made : I barely made pedals working at the 1st time... The preliminary checking that I have done did not revealed the fault (a "big-joke-style" bug), so I will do some signal-tracing this afternoon, and supsect everything... As usual !

A+!

Thx, this is comforting, this is my first self-etched project i did. Anyways, capacitor seems to be doing noting.

As far as diodes are concerned I see nothing funny about them?

Also, what is a good start when debugging these sort of problems? Are my layout and schematic all right at least? On ggg's layout there is another diode and electrolytic cap (link: http://www.generalguitargadgets.com/pdf/ggg_dist_g250_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a) they are set as "optional" so I didnt bother, are those of any relevance?

Hey, feel free to use my layout and maybe get it working (I can send you project file via PM)

Thx for your replys

Izidor

[ZeusMalt]

oops, i ment the other sde. The pic is a bit blurry, are the solderings ok.. Nothing touching that shouldn't be touching?

[Quackzed]

if those green wires are carrying bosth input and output wires, that could be your oscillation prob...

[ZeusMalt]

if those green wires are carrying bosth input and output wires, that could be your oscillation prob...

That's hard to believe, unless the cables are damaged... Although... Who knows. Have you verified the schema-pcb?

[tiges_ tendres]

Given that all of the wiring is stuffed in heat shrink and is all the same color. How can you tell that each wire is going to the right place on its other end?