Clone DOD 250 Overdrive - Component Materials?

[Steve Mavronis]

Please go over my parts list and help me check for any mistakes or ommisions. Thanks...

DOD 250 Overdrive Clone Bill Of Materials:

C1      .047uF      Ceramic
C3      .01uF      Ceramic
C4      10uF      Polarized Electrolytic 16V   
C5      4.7uF      Polarized Electrolytic 16V
C6      .001uF      Film

D1      1N4148      Silicon DO-35 Glass Case Small-Signal
D2      1N4148      Silicon DO-35 Glass Case Small-Signal

P1      500K      16mm Angled Lead Reverse Log   
P2      100K       16mm Angled Lead Audio   

R1      4.7K      1/4 Watt Carbon Film
R2      1M      1/4 Watt Carbon Film
R3      10K      1/4 Watt Carbon Film
R4      100      1/4 Watt Carbon Film
R5      22K      1/4 Watt Carbon Film
R6      470K      1/4 Watt Carbon Film
R7      22K      1/4 Watt Carbon Film
R8      10K      1/4 Watt Carbon Film

U1      LM741CN      Single Channel 8-Pin Operational Ampplifier

PCB      Custom Layout

Input Jack      1/4" Stereo
Output Jack   1/4" Mono
Footswitch      3PDT      Heavy Duty
LED      Blue      
AC Jack      2.1mm Barrel   Boss Style
Battery      9V
Wire      24 Gauge
Enclosure      Hammond 1590B
Knobs      2      1" DOD/Boss or 1" MXR Style

Miscellaneous   Lock Washers, Nuts, Washers, Battery Clip

[BAARON]

- Using enclosed jacks (the black plastic ones) will require less space than open-frame jacks, which is helpful when using something shallow like a 1590B enclosure.
- Don't forget standoffs for the board if you need them.
- You might want a bezel to go with your LED.
- You also need a current-limiting resistor for your LED.  Something in the 1k5-2k7 range for a high brightness blue LED, I would suggest.

[Steve Mavronis]

Thanks Baaron I forgot about that bezel and limiting resistor! I'm thinking about relocating the power jack to the rear of the unit for extra room and it's out of the way. I didn't realize that enclosed jacks take up less space. I think that this article by Gaussmarkov about wiring up a 1590B is a great guide with fantastic 3D illustrations:

http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b/

I wonder if he has them in 2D format so I can use them for measurements?

[Speeddemon]

I looked at the GGG "Gray" schematic, and I can't for the life of it understand how they came up with all these extra parts (aside from the omittable ones), like the 2,2nF cap grounded near the input, or the 22uF electrolytic instead of the original 4.7uF and the 2,2nF cap near the diodes (originally 1nF). And what's up with the 20k resistors (instead of the common AND originally used 22k)?! 
Steve, your schematic looks fine.

[Steve Mavronis]

I looked at the GGG "Gray" schematic, and I can't for the life of it understand how they came up with all these extra parts (aside from the omittable ones), like the 2,2nF cap grounded near the input, or the 22uF electrolytic instead of the original 4.7uF and the 2,2nF cap near the diodes (originally 1nF). And what's up with the 20k resistors (instead of the common AND originally used 22k)?!  
Steve, your schematic looks fine.

Thanks. My clone pedal project (sort of evolving still) is documented now in this thread (http://www.diystompboxes.com/smfforum/index.php?topic=82633.0) but I know what you mean about the various part differences in the GGG clone and if you search the layout gallery here for 250 you will see at least 3 different layouts using different parts! For me there is confusion between the 1977 gray and the "gray spec" version. I decided to go with PCB pictures from the later gray 250's that seem to be the same as the first yellow 250's with 22K voltage dividers and that extra 100 ohm resistor to V+.

[Speeddemon]

Hey Steve, you are aware that Small Bear now (well 'now' being relative, as I've been out of the loop for 2,5 years) sells the correct knobs, right?
http://www.smallbearelec.com/Detail.bok?no=739

Also, if I'm not mistaken, the gain pot should be 500k lineair, instead of 500k reverse log. With the lineair pot the distortion 'travel' is more evened out AND is vintage correct, at least from my personal research.

(EDIT: YAY! 100th post!  )

[Steve Mavronis]

Yeah I bought those same knobs from Small Bear! They also have the right angle mount pots that I'm using. Here is a picture of my partially built 1590B box in black:



I've always heard the original DOD gray 250, yellow 250, and re-issue yellow 250, YJM308 all use a 500K reverse audio log gain pot. A linear one won't sound correct to the human ear. You wouldn't percieve much gain until the last 1/2 turn or more. With a reverse log gain it appears as an even transistion from low gain to high gain. It's hard to explain but true. Here is an excerpt from The Secret Life of Pots (http://www.geofex.com/Article_Folders/potsecrets/potscret.htm) web article. I know it says volume controls but think of gain as an incease in the amount of distortion volume:

Volume controls are different. The human ear does not respond linearly to loudness. It responds to the logarithm of loudness. That means that for a sound to seem twice as loud, it has to be almost ten times the actual change in air pressure. For us to have a control pot that seems to make a linear change in loudness per unit of rotation, the control must compensate for the human ear's oddity and supply ever-increasing amounts of signal per unit rotation. This compensating resistance taper is accurately called a "left hand logarithmic taper" but for historical reasons has been called an audio or log pot. In these pots, the wiper traverses resistance very slowly at first, then faster as the rotation increases. The actual curve looks exponential if you plot resistance or voltage division ratios per unit of rotation.

[zombiwoof]

I recall that in another thread it was mentioned that the reverse log works better when you are using the pedal into high gain, but the linear will work fine into a less gainy setup.  With the reverse log, the settings are spread out more and easier to dial in subtle differences.

Al