250 coming along...

[thermionix]

Got the board built today.  Works and sounds great!  Coming up with the perf layout took much longer than actually building it.  Who else uses graph paper?

I breadboarded it with a 1458, but built it with a 741.  Sounds the same to me, but with about two weeks between each listen, could be some subtle difference.  741 was a pain to lay out efficiently on perf.  I ended up with two +9V wires, but was able to bus all the grounds together (not counting pots, jacks, LED...all offboard).

Most of the schematics I found online were wrong, or variations, but I gleaned what I could from them and applied that to pictures I found of "gray box" originals.  Mine is a note-for-note copy, as far as I can tell, except with a 1M pulldown added on the input.

Enclosure tomorrow.

[rutabaga bob]

+1 for the graph paper!   

[PRR]

> Who else uses graph paper?

[blackieNYC]

+1 on the graph paper.
But not perf layouts so much. If I think it's going to be tight on one of those perf boards you've got there, I might use a mechanical pencil and poke thru the perf holes to make a grid. And then draw little boxes for components - resistors take 4 holes, unless I stand them upright, op amps take up this many holes, etc.  it's a small diagram but I know I'm working in actual size.  I can place something exotic like a vactrol on there and see how much space it eats up.
But I guess I've found I can do any circuit with two dual op amps on that small 45mm square perf, so I just give each TL072 (socket) as much room as possible, solder them in, and just kinda go at it. I do end up with just a few insulated jumpers on the underside, sometimes crossing over each other. Trying to keep the build small. 

[anotherjim]

I tip my hat to those who can habitually build from either published or hand rolled  perf or vero layouts. All that checking back & forth as you go makes my eyes go wobbly. I don't know why or how, but I really find it quicker & more reliable to freestyle the layout as I solder. Yeds, a rough layout on graph paper just to get an idea of how much room there is and best position for IC's & things. Sometimes I do paint myself into a corner & need to run a wire or too around things. Once size & arrangement is decided, I fit a few major things -  usually an IC socket and add stuff from there.

[EBK]

I use engineering paper. It's like graph paper, but more satisfying, in my opinion . It's basically very smooth graph paper with the grid printed on the back (faintly visible from the front), with a heavier line every 5 squares.  Comes in various colors.  I like to call it my "thinking paper."

[bool]

+1

5x5 grid paper is the best

[bloxstompboxes]

I have some but have not yet used it. I will say that cozybuilder uses it for sure. Haven't seen him around much lately though.

[duck_arse]

since I started using DIYLC, -1 on the graph paper (although I was using gridded paper). it didn't stand up to all the erasering too well, and when I go back and look at those old dias, I can barely make out anything in all the grey fog.

[PRR]

> pencil and poke thru the perf holes to make a grid.

Most electronics holy-board is 0.1" centers.

0.1" grid paper is a standard thing.

While graph paper is getting hard to find for real, there are online PDF generators to give you graph paper files. Just be careful of your PDF tool trying to re-size for printer.

[thermionix]

Done.



Gray box for mojo.  Knobs may be changed at some point.  No graphics, but everything is where you'd expect it to be.

With a little more playing time, I think the 741 gives just a wee bit more distortion than the 1458 did, but that could just be the fresh battery.  This is quickly becoming a favorite box for me, the bass cut is actually ideal for my rig.

[GiovannyS10]

Looks awesome! 

[thermionix]

Thanks Giovanny!  The gray and black combo has kind of a "military avionics" look to me, a little more so in person than in the crappy picture I posted.  I dig that.

[Ben Lyman]

That looks great, don't change the knobs! It's the "250 Deluxe"   
So, I have boarded both the 250 and the Dist+ a few times and not been very happy.
I owned both of those in the 1980's and I remembered it being better than what I have recently boarded.
Maybe because the schematics around the web are a little off?

[thermionix]

That looks great, don't change the knobs! It's the "250 Deluxe"   
So, I have boarded both the 250 and the Dist+ a few times and not been very happy.
I owned both of those in the 1980's and I remembered it being better than what I have recently boarded.
Maybe because the schematics around the web are a little off?

Speaking of "a little off"...I just noticed a mistake I made.  The output cap is supposed to be a 4.7uF and I used a 10uF.  Oops.  Without doing the math, I'm inclined to believe that it makes no difference, whatever rolloff frequency is changed there is probably well below anything coming out of the opamp.  Someone feel free to correct me if I'm wrong.

Also, most schematics I've seen online (including the actual DOD schematic), have the output from the 741 going cap>resistor, and that's how I did mine.  But looking again at the pictures of originals, they are built with the resistor first.  That should make zero difference, people here tell me that with components in series, the order doesn't matter.

The resistor feeding the bias is usually 470K, but in some units is 430K.  I used 430K because the picture I was looking at had that.  I've seen mention of some with 510K, but I haven't seen a picture to back that up.  I'm assuming that this variation makes no audible difference whatsoever.  The Dist+ used 1M there.

Seems DOD used a variety of clipping diodes, so I can't say any type is correct, just Si and symmetrical.  I had some NOS 1N914s, so I used those.  Whatever.

Do you remember which schematic(s) you were using?  Two of the incorrect versions I found were the vero layouts in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=97024.0

Those layouts have the output drawn from between the cap and the 10K resistor, which just ain't right.  I'm sure it would function, my guess is that it would clip a little less and have a somewhat different tone.

[Ben Lyman]

I think I used this one from fuzzcentral. I like the site and usually have good results with the schematics:
http://fuzzcentral.ssguitar.com/schematics/od250schem.gif

Here's another site that I go to for schematics, so I might have tried this version too:
http://gaussmarkov.net/layouts/dod250/dod250-schem.png

[karis12]

A 10uf output capacitor after the opamp seemed to make the pedal too "fat" in my experience, so I switched it out for the correct value.

Slight threadjack, but has anyone noticed any difference between 22kohm vs 1megohm voltage divider resistors for this circuit? It seems to be a major difference between the DOD and the MXR Dist+, aside from the clipping diodes.

[thermionix]

http://fuzzcentral.ssguitar.com/schematics/od250schem.gif

Add a 1M pulldown, change the 470K to 430K, and that's exactly what I built.  So that schematic is correct, except the output cap should be 4.7uF.

One thing to note, I've never played a real 250 before, so I didn't really have any preconceived notions, and I can't compare my build to a "real" one.

http://gaussmarkov.net/layouts/dod250/dod250-schem.png

That's one of the variations I've seen.  I don't think any of the originals had asymmetric clipping.  The 25pF cap is from the reissues that use a 4558 I believe.  I don't think it's supposed to be there for a 741, but probably not a big deal.

[thermionix]

A 10uf output capacitor after the opamp seemed to make the pedal too "fat" in my experience, so I switched it out for the correct value.

Well dang, I was hoping someone would come along and tell me it makes no difference.  Swapping parts on perf is kind of a bitch, especially when it's already boxed up!  I've mostly been playing it with the gain full up so far, and I don't think anybody would call that sound "too fat" but at the lower gain settings you might be right.

So let's see what the resident EEs with all the formulas have to say:



10uF vs 4.7uF on the opamp output...any difference?

[lars-musik]

That looks like a fine pedal. Well done indeed.

I recently finished a yellow-grey box. I was interested in the differences between the two DOD250s. But as usual my ears (or my amp or my playing)  didn't play along. I think the differences are negligible. The two slider change the cap values between Y (yellow) and G (grey) and the toggle switches between Germanium-OFF-Silicon clipping.

I really like the sound of this one, too.